Open access peer-reviewed chapter

Dilute Magnetic Semiconducting Quantum Dots: Smart Materials for Spintronics

Written By

Jejiron Maheswari Baruah and Jyoti Narayan

Submitted: October 10th, 2017 Reviewed: December 20th, 2017 Published: April 4th, 2018

DOI: 10.5772/intechopen.73286

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Abstract

The present day world involved in the fabrication of miniaturized smart devices is in continuous quest of materials with better optoelectronic and magneto-electronic efficiency. Effective incorporation of dopants into semiconductor lattices have been accepted as a primary means of controlling electrical, optical, magnetic and other physico-chemical properties of semiconductors. Manipulations in magnetic spin within a semiconducting material have lead to an effective research for potential ferromagnets with semiconducting properties, leading to an important field, dilute magnetic semiconductors (DMS). On the other hand, quantum dots (QDs) have been registered to be quantum confined nanocrystals with unique optoelectronic properties, having a wide range of potential applications. QDs experienced rapid development leading to the concept of dilute magnetic semiconducting quantum dots (DMSQDs), where transition metals with a few to several atomic percentages, having unpaired d-electrons, are doped in order to manipulate their opto-magnetic properties. These materials are fabricated by alloying transition metals with Group II-VI, III-V and IV-IV elements resulting in multi-component systems. They have tremendous applications in the spintronics industry, where electronic properties are controlled by spin degree of freedom. The present report reveals the significance, electronic origination of the fact, synthesis and their applications toward the fabrication of spintronics devices.

Keywords

  • dilute magnetic semiconductors
  • quantum dots
  • dilute magnetic semiconductors quantum dots
  • spintronics
  • opto-magnetic properties

1. Introduction

The dilute magnetic semiconductor quantum dots (DMSQDs) are basically the combination of semiconducting quantum dots, where transition metals are introduced as impurity or dopants. They are symbolically represented by A1−xMxB or A(M)B or AB(M), where A is often a non-magnetic cation, A and B can be from Group II-VI, Group III-V and Group IV-IV elements. These nanoscale materials play an important role in microelectronics and magnetic storage devices [1, 2, 3]. Additionally, these materials have the quality to exist in both Curie temperatures (Tc) as well as in room temperature (RT) with high saturation of magnetization (Ms) [4, 5, 6]. These quantum confined materials has unique magneto-optical and optically controlled magnetism properties, which make them essentially important in today’s research on materials for spintronics (spin-based electronics) [7, 8] device making. The device making includes miniaturization of electronic devices, magnetic fluids and high density data storage systems [9, 10, 11]. The semiconducting quantum dots which are being in research are from the Group II-VI and the dopants are transition metals. The individual potentiality of these materials, generated by coupling of diluted magnetic semiconductor (DMS) and quantum dots (QDs), is expected to be a path breaking one in the future field of optoelectronics and magneto-optoelectronic devices. To understand better, we will first look into the concept of DMS and QDs separately.

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2. Dilute magnetic semiconductor (DMS)

Magnetic semiconductors are the semiconducting materials, which can exhibit ferromagnetism. Doping of the transition metals in these materials are said to be dilute magnetic semiconductors (DMS). The DMS are therefore semi-magnetic due to the introduction of magnetic elements in their lattices. Basically, the spintronics property of these materials has attracted the present day research for possible technological applications. By definition, spintronics is a combination of electrons’ spin and their associated electronic charge and magnetic moment.

The first generation spintronics devices are derived from passive magnetoresistive sensors [12], but the second generations devices are expectedly achieved with the active spin-based devices, which are manipulated in the host semiconductor with spin-polarized electrons [13, 14]. The thought behind a spintronics device is the presence of spin-polarized electrons which travels through the host. Although the introduction of the ferromagnetic material in the semiconductor material through doping is extensively studied, yet the electronic spin is difficult to preserve throughout the material interface due to the difference in electrical conductivity in both the doped as well as the host material [15]. Hence, to present these materials as expected material, better than both ferromagnetic and semiconductor individually, research is very much crucial and warranted in spin electronic carrier device industries. DMS is next concept to meet the vital applicative operation to establish the spintronics carrier devices, an efficient one. In DMS, the host is non-magnetic semiconductor, whereas, the magnetic material is from transition metal series. These are powerful integrated devices having highly spin-polarized capacity.

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3. DMS materials and their applications

3.1. AII1−xMnxBVI ternary materials

One of the most extensively studied DMS is alloys of AII1−xMnxBVI (A- Group II element & B- Group VI element) [16]. This ternary material exhibits both wurtzite and zinc blende crystalline structure as per their compositional range [17]. It is noticed that the change in Manganese (Mn) content can lead the crystal structure to cubic or hexagonal orientation. It has been observed that lower the input of Mn element in the host composition, the resultant structure tends to acquire cubic crystallinity, whereas, with higher the amount of Mn doping wurtzite crystallinity is observed [18]. Crystal structure of the various compositional ranges of the material suggests that, although their symmetry is different, both achieve tetrahedral geometry (s-p3bonding) with the involvement of 2svalence electrons from Group II element and 6pvalence electrons from Group VI element. Mn acts as a contributor of its valence 4s2electrons to the s-p3bonding arrangement, although Mn differs from Group II material with an exactly half-filled d-orbital. The Hund’s rule suggests that introduction of an unpaired electron of opposite spin will require a lot of input of energy (~ 6–7 eV) and hence Mn is acting as complete 3dshell material [19]. This ability makes Mn eligible for the replacement of Group II elements in the tetrahedral structure. There is another crucial reason behind the establishment of Mn as a replacement of other Group II materials, which is the exact half-filled 3dorbital configuration of Mn. The fact is as important as, there is a possibility of forming stable phase by other elements too, although, dimer formation is very much a possibility for other than Mn of the Group II element [18].

3.2. TiO2 base DMS

Among the oxide base DMS materials, Cobalt (Co) intruded Titanium dioxide (TiO2) system is one of the most consistently researched n-typesemiconductor, to achieve ferromagnetism far above the RT (Tc > 650 K) [20]. The importance of temperature in this kind of system is because the system of magnetic semiconductor is hard to achieve at RT [21, 22]. The reason behind such concept is the faced difficulty in the introduction of both electronic and magnetic dopants in the system and functionalization of the designed material as a good balanced material between dopant spins and free carriers of electrons. Hence, the synthesized material achieves the coupling as a thermally strong dopant spin-carrier coupling [22]. The most recent research suggest that the ternary cited materials of Mn-doped Group II-VI semiconductors are also capable of exhibiting the expected necessary property as Co-doped TiO2 revealed at RT [23, 24].

TiO2 is a wide direct forbidden band gap (3.03 eV) material, used for optoelectronic devices and solar cell applications [25, 26, 27]. Its crystal symmetry is found to be in tetragonal and rhombohedral orientations [28]. Therefore the thin films of Co-doped TiO2 can be accommodated in the applicative DMS devices. The first observation of RT ferromagnetism in the Co-doped TiO2 system was reported at Anatase phase Ti1−xCoxO2 films (0 ≤ x ≤ 0.08), on LaAlO3 and SrTiO3 substrates, using laser molecular beam epitaxy, at substrate growth temperatures between 680 and 720°C [29]. Same research group also found the satisfactory results with the thin films of rutile phase TiO2 with a composition of Ti1−xCoxO2 (0 ≤ x ≤ 0.05) onto α-Al2O3 substrates, using the same deposition technique [30]. After this achievement, a good number work on this composition was done with various thin film deposition techniques, viz., pulsed laser deposition (PLD) [31, 32, 33, 34, 35, 36], laser molecular beam epitaxy (LMBE) [37, 38, 39], metal–organic chemical vapor deposition (MOCVD) [40], reactive co-sputtering, oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) [41] and sol–gel [42] method. Researchers observed that the pressure of Oxygen applied during the thin film deposition is also a very important factor and suggested that at PO2 ≥ 1.3 × 10−5 mbar, we can have clear streaky RHEED patterns, which suggest two-dimensional smooth surfaces [32].

The ferromagnetism in Co-doped TiO2 is a topic of interest for the research accompanying spintronics devices. The oxide base DMS materials have extrinsic or intrinsic effect, which is the root of their device driven capability, is still a matter of discussion. The extrinsic effect may be attributed to the interaction of local magnetic moments with magnetic impurities. The intrinsic magnetism may be due to the exchange coupling between the spin of carriers and local magnetic moments. Since, spintronics takes place only in polarized charge carriers, which is possible only when the ferromagnetism is intrinsic. The issue is of great concern because the experimental evidence is not yet available behind the actual reason of magnetism of DMS in TiO2. Anomalous Hall effect (AHE) and electric field induced modulation by magnetization suggests, for rutile phased Co-doped TiO2 system, the carrier-mediated ferromagnetism with a value of 13.5% [43, 44].

Recent theoretical studies propose the creation and distribution of oxygen vacancies in Co-doped TiO2 is responsible for the ferromagnetism in these systems. The ferromagnetism is suppressed when the oxygen content is increased in the unit cell [45]. In a nutshell, for the TiO2 crystal, in the event of an oxygen vacancy, Ti atoms will give away their electrons to oxygen and hence they will be in the scarcity of electrons to get bind with the oxygen vacancy sites by their own atoms and therefore a situation of hydrogen-like orbital occurs, hence constitutes a Polaron. This phenomenon is supported by a percolation model named bond magnetic polaron (BMP), which was used to study the magnetically doped oxides [46].

In the interaction of the magnetic cations with the hydrogenic electrons in the impurity band, the donors tend to form BMPs, coupling the 3d moments of the ions within their orbits. Depending on whether the cation 3d orbital is less than half filled, or half filled or more, the coupling between the cation and the donor electron is ferromagnetic or anti-ferromagnetic, respectively. Either way, the coupling between two similar impurities within the same donor orbital is ferromagnetic. The polaron radius is a function of the host material’s dielectric constant and electron effective mass. If the polaron concentration in the material is large enough to achieve percolation, an entire network of polarons and magnetic cations become interconnected and we observe macroscopic ferromagnetic behavior [47].

Thus, the incorporation of impurities/dopants in the semiconducting lattices have been realized as an important primary means of controlling the magnetic and electrical conductivities, besides having an immense effect on magnetic, magneto-optical and other physical properties of semiconductors.

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4. Quantum dots

Quantum dots (QDs) of semiconducting materials have attracted the research community due to their potential application in various fields of humanity, viz., optoelectronics, solar cell, bioimaging and biosensors, cosmetics, space science, photocatalytic activity, etc. [48, 49, 50, 51, 52, 53, 54]. The QDs can be defined with respect to their size, which is supposed to be less than excitons Bohr radius. The material specific Bohr radius also leads to the property of that material. The size factor is supported by differently shaped particles. The size of the QDs leads to the significant change in band gap of the semiconductors than the bulk. The enhanced band energy of the particles is due to the fact of their atom like structures. These particles in this confinement have 10–1000 numbers of atoms within one particle. Therefore, the energy levels of each particle have the merging levels of only some of the atoms in comparison to their bulk entity, where millions of atoms coincide. Because of this fact, very less energy levels can merge with each other in a QD and hence the band gap energy increases drastically. The QDs have another specific property of showing blunt and broad absorption peak. The primary cause behind the phenomenon resides in their size effect. At the atomic level, the slight change in the size of a particle (viz., 0.5 nm) can change their HOMO-LUMO gap drastically. Therefore, whenever there is a solution of QDs, the particle size is never homogeneously uniform in the solution. Hence, for every particle the band gap energy will be different and therefore the absorption maximum shifts accordingly. As a consequence of the presence of differently sized particles in the solution, togetherness of these absorption maxima can be observed and hence a broad peak. Therefore, by tuning the size, we can meet the desired application with these particles. Apart from the size factor, shape phenomenon also plays a significant role in deciding the characteristic features in the field of quantum dot physics. The electrons, which are the driving force behind every electronic transition in a physical matter, have received different orientations in terms of surface of the particle. In the quantum range of physics, the QDs are forced to adapt the required application by modifying their surface. The reason behind such observation is the attachment of the surface electrons for differently shaped particles is different, which is again as an outcome of releasing surface energy of the particle to make it stable. The introduction of capping agents (the ligands) is also having a capability of taming the particle according to their preferred shape. This phenomenon is addressed as surface functionalization. The surface modification can lead us to the fabrication of the particles with better efficacy in different applicative devices.

The property of showing high luminescence by these QD metamaterials is one of the most aspired properties. The generation of double excitons leads the materials toward more promising luminescent material. This extraordinary property blesses these materials to show higher emission range than the traditional dyes and hence they become more appropriate with the fact of getting more emission with the excitation of only one electron. The size and, of course the shape, both have an important role in making them suitable for these applications. Most of the time the tunable size property of these quantum dots is mentioned, due to which one can access the whole light spectrum. The devices such as LEDs and solar cell require these nano dots in such a manner that they have the ability to absorb the whole visible and UV region and emit the same in higher wavelength. Therefore, the luminescence property of these fluorescent dots has to have the tenability to perform in the whole region. Fortunately, researchers found that for different semiconducting quantum dots, we can achieve the luminescence as per our requirement. Another interesting concept of wastage of the solar energy as thermal energy during the absorption of sun light by a photovoltaic cell comes into play, in the present day photo voltaic research. It is observed that a photovoltaic material, such as, QDs (although being the most promising one), cannot absorb the whole sun light as conversion efficiency of the cell becomes less. The reason behind this is the material, that we are using, can absorb the light in the desired range but cannot emit the same in the desired wavelength. To tackle this difficulty, the concept of large stock shift quantum dots has come up. This large stock shift materials can absorb the sun light in short wavelength and emit the same in the long wavelength, which make these functionalized quantum dots more efficient toward these kind of applications [55].

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5. Dilute magnetic semiconductor quantum dots (DMSQDs)

Discussions on DMS and QDs have made it easier to understand the concept of DMSQDs. They are quantum dots of semiconducting materials doped with transition metals having magnetic behavior. Due to specific significance of QDs, researchers are tremendously focusing on the ferromagnetic material doped QDs. Since, semiconductors do not possess high magnetism in any level of their atomic growth, it becomes essential to incorporate the magnetic nature of DMS in nanoscale so as to improve its efficiency in the various fields of spintronics applications. It has been observed that the effectiveness of interaction of sp-dfor the exchange of carrier and magnetic ions in terms of hole energy depends on the high and low magnetic field induces from outside. Hence, it is expected that due to the small size of a quantum dot, the exchange and interaction of delectrons with spshelled electrons will be extensive in DMSQDs [56]. Therefore, the spintronics devices developed from DMSQDs are expected to be efficient as well as miniaturized one, probably due to the quantum confinement effect of DMS and therefore better than the single DMS materials.

5.1. Synthesis of DMSQDs

The synthesis procedures are very much similar to those for the synthesis of QDs. The only exception is to incorporate the metallic materials as impurity during the reaction process. Among a vast number of procedures, the chemical route to synthesis DMSQDs is the most commonly use deficient method. The size and shape of such QDs can be easily tailored through this method. Unwanted oxidation can also be prevented during the adopted during the synthesis process. Fe, Co, Ni and Mn are the main doping elements used for the preparation of DMSQDs of semiconductors of Group II-VI [56].

Clustering and surface doping are two main issues that are faced during the synthetic process for obtaining uniformed DMSQDs. To eliminate these key issues, one has to overcome self-purification [57] of the materials and understand the reactivity between the host-guest materials [58, 59]. The self-purification is a process where host molecule expels the guest molecule from the surface to attain a thermodynamically stable state by reducing its defect energy. Self-purification can be resolved by making the magnetic core at first, followed by coating with the semiconducting material and then annealing at higher temperature for a longer time to diffuse the dopant inside the host properly before it get expelled by the host. The reactivity issue can be sorted out by two ways: a) Nucleation doping and b) Growth doping. Successive ionic layer adsorption reaction (SILAR) method was used to dope Fe in CdS in one of the methods of its preparation. This was attained at high temperature. This method showed excellent result with the homogeneous diffusion of Fe in CdS shell. It was also reported that the oxidation state of Fe was reduced to 2 from 2.44 due to the presence of reducing reagent and replaced the Cd site with substitutional doping.

5.2. Properties and applications of DMSQDs

DMSQDs possess unique properties which make them suitable for wide range of applications. Their properties are primarily divided into magnetic and magneto-optical as well as magneto-electrical properties. These properties are attributed to the exchanged interaction of sp-dbetween the dopants magnetic material and the host semiconductor, although proper mechanism of origin of the effect and the governance of ferromagnetism are not yet confirmed. Secondly, it has been observed that due to the presence of quantitatively unknown weights of ligands within the synthesized material makes it difficult to calculate the conversion of magnetic moments from magnetic ions, [60] however there have been improvement toward the production of DMSQDs from time to time. Early reports on quantification showed the presence of a few magnetic moments in emu/gram (memu/g) [61] due to the doping of magnetic ions, instead of much more as expected. The effect of unknown amount of magnetic moment hinders the knowledge of comparison between the absolute magnetism of bulk and nano materials. The plausible reason to this effect may be the clustering of magnetic dopants or/and inherent sp-dexchange interactions.

One of the most advantageous finding on DMSQDs shows an exceptionally different nature of magnetism. It is the co-doping of ZnO with Cu and Fe [62]. Interestingly, ZnO individually doped with Fe or Cu showed an anti-ferromagnetic behavior without a trace of ferromagnetism. Whereas, the co-doping of both the transition metals in ZnO showed high quality ferromagnetism with magnetic moment as high as 600 memu/g. This work has proved the anti-ferromagnetism of Cu doped ZnO with the help of Mversus H(Magnetization versus Magnetic field intensity) plot and anti-ferromagnetism of Fe doped ZnO with the inverse susceptibility plot as function of temperature, showing a negative intercept. But, in co-doped ZnO with Cu and Fe, X-ray absorption spectroscopy (XAS) clearly showed the presence of both Fe+2 and Fe+3 and its relative percentage is dependent on the presence of Cu as a dopant. Another research revealed that the size of Fe doped CdS QD was responsible for the magnetic moment [57]. They have achieved a magnetic moment of 80 memu/g at RT for doped CdS and un-doped CdS showed negligible amount of magnetic moment with the same scale reaction. It has been observed that in the presence of an external magnetic field, a non-magnetic substance showed a small internal magnetic field due to Zeeman splitting (having an order of 2), whereas, materials like DMSQDs, the intensity of internal field is very high in the presence of external magnetic field [56]. It is also observed that along with the large internal field, a small external magnetic field also gets generated during this process. This happens due to the presence of the magnetic ions inside the material and the tendency to align themselves in the direction of the applied magnetic field. Theoretical modeling of magneto-optical and electronic property of core-shell nanoparticles of CdS-ZnS, doped with magnetic impurities of Mn showed that, these nanocrystals can give an attuned value of gover a wide range and make them suitable for spintronics devices, if the position of the magnetic impurities can be controlled [63]. Spectral fingerprints of the spin–spin interactions between the host excitons and the dopant is also revealed by single particle spectroscopy with discrete projections of individual Mn+2 ions observed from emission peaks. These QDs showed enhancement in exchange splitting at elevated temperatures by an order of magnitude compared to their epitaxial counterparts, which is useful for solotronics applications. The circularly polarized photoluminescence in the presence of magnetic field (MCPL) for bulk DMS is very much different than the QDs. In case of DMS material, the emission band edge of the host material showed a polarization due to the splitting of the band, but doped material (Mn+2) do not show any band polarization due to spin and orbital forbidden emission [64]. But, in DMSQDs, along with the host, the dopant also showed polarized emission band edge in the presence of magnetic field. This surprised effect was although not yet properly understood, but expected to be due to quantum confinement, where wave functions are overlapped extensively [65]. Magneto-optical response in Cu doped chalcogenide QDs is also a tremendous effect observed in DMSQDs. This photo-excitation phenomenon in these DMSQDs has come as a result of strong spin-exchanged interaction between the valence band-conduction band (VB-CB) of the host and the paramagnetic Cu dopant. The magnetic circular dichroism (MCD) studies revealed the enhancement of paramagnetism up to 100% in these Cu doped ZnSe/CdSe QDs under the UV light excitation. Again, in dark, these materials retained a photo-magnetization memory for timescales of hours [66]. Another application is reported for Mn-doped CdSe QDs as light-induced spontaneous magnetization, where spin effect is controlled to generate, manipulate and read out spins [67]. In this case, no external magnetic field was applied but still showed large Zeeman splitting as a result of photo-excitation. The reason behind these giant splitting is the generation of large dopant-carriers exchange fields. These materials are having potential applications in the field of magneto-optical storage and optically controlled magnetism. DMSQDs are also known to respond to charged carriers. The carrier-mediated ferromagnetic interaction in Mn-doped CdSe QDs are also reported, which arise due to photo-excited carriers from surface defect states of smaller QDs (~3 nm) [68]. Mn-doped ZnO QDs also exhibited ferromagnetic exchange interaction due to photo-excitation in the absence of oxygen [69] and as is reported in air-stable Fe–Sn co-doped In2O3 [70]and Mn–Sn co-doped In2O3 [71]. Research has proved the conduction band electron–dopant ferromagnetic exchange interaction, offers magneto-electric and magneto-plasmonic properties which helps in wide scale spintronics applications.

References

  1. 1. Mandal SK, Mandal AR, Banerjee S. High ferromagnetic transition temperature in PbS and PbS:Mn nanowires. ACS Applied Material Interfaces. 2012;4:205-209
  2. 2. Zhou Y, Liu K, Xiao H, Xiang X, Nie J, Li S, Huang H, Zu X. Dehydrogenation: A simple route to modulate magnetism and spatial charge distribution of Germanane. Journal of Materials Chemistry C. 2015;3:3128-3134
  3. 3. Odio OF, Lartundo-Rojas L, Santiago-Jacinto P, Martínez R, Reguera E. Sorption of gold by naked and Thiol-Capped Magnetite nanoparticles: An XPS approach. Journal of Physical Chemistry C. 2014;118:2776-2791
  4. 4. Dietl T. A ten-year perspective on dilute magnetic semiconductors and oxides. Nature Materials. 2010;9:965-974
  5. 5. Felser C, Fecher GH, Balke B. Spintronics: A challenge for materials science and solid-state chemistry. Angewandte Chemie International Edition. 2007;46:668-699
  6. 6. Gao D, Yang G, Li J, Zhang J, Zhang J, Xue D. Room-temperature ferromagnetism of flowerlike CuO nanostructures. Journal of Physical Chemistry C. 2010;114:18347-18351
  7. 7. Sinova J, Zutic I. New moves of the Spintronics tango. Nature Materials. 2012;11:368-371
  8. 8. Wong PKJ, Zhang W, Wang K, van der Laan G, Xu Y, van der Wiel WG, de Jong MP. Electronic and magnetic structure of C60/Fe3O4(001): A hybrid Interface for organic Spintronics. Journal of Materials Chemistry C. 2013;1:1197-1202
  9. 9. Schwartz DA, Norberg NS, Nguyen QP, Parker JM, Gamelin DR. Magnetic quantum dots: Synthesis, spectroscopy, and magnetism of Co2+− and Ni2+−doped Zno Nanocrystals. Journal of the American Chemical Society. 2003;125:13205-13218
  10. 10. Schwartz DA, Kittilstved KR, Gamelin DR. Above-room-temperature ferromagnetic Ni2+−doped ZnO thin films prepared from colloidal diluted magnetic semiconductor quantum dots. Applied Physics Letters. 2004;85:1395-1397
  11. 11. Ohno H. Making nonmagnetic semiconductors ferromagnetic. Science. 1998;281:951-956
  12. 12. Chappert C, Fert A, van Dau FN. The emergence of spin electronics in data storage. Nature Materials. 2007;6:813-823
  13. 13. Bland T, Lee K, Steinmuller S. The spintronics challenge. Physics World. 2008;21:24-28
  14. 14. Awschalom DD, Flatté ME. Challenges for semiconductor spintronics. Nature Physics. 2007;3:153-159
  15. 15. Wolf SA, Awschalom DD, Buhrman RA, Daughton JM, von Molnár S, Roukes ML, Chtchelkanova AY, Treger DM. Spintronics: A spin-based electronics vision for the future. Science. 2001;294:1488-1495
  16. 16. Furdyna JK. Journal of Vacuum Science and Technology A;42002 (1986)
  17. 17. Pajaczkowska A. Physicochemical properties and crystal growth of AIIBVI-MnBVI systems. Progress in Crystal Growth Characteristics. 1978;1:289
  18. 18. Furdyna JK. Diluted magnetic semiconductors. Journal of Applied Physics. 1988;64:R29-R64
  19. 19. Hass KC, Ehrenreich H. Journal of Crystal Growth. 1988;86:8
  20. 20. Fukumuraa T, Yamadaa Y, Toyosakia H, Hasegawab T, Koinuma H, Kawasakia M. Exploration of oxide-based diluted magnetic semiconductors toward transparent spintronics. Applied Surface Science. 2004;223:62
  21. 21. Seife C. 125 big questions that face scientific inquiry over the next quarter-century. Commemorative Issue Celebrating the 125th Anniversary of the Science Magazine. Science. 2005;309:82
  22. 22. Chambers SA, Droubay TC, Wang CM, Rosso KM, Heald SM, Schwartz DA, Kittilstved KR, Gamelin DR. Ferromagnetism in oxide semiconductors. Materials Today. 2006;9:28
  23. 23. Edmonds KW, Wang KY, Campion RP, Neumann AC, Farley NRS, Gallagher BL, Foxon CT. High-curie-temperature Ga1–xMnxAs obtained by resistance-monitored annealing. Applied Physics Letters. 2002;81:4991
  24. 24. Chiba D, Takamura K, Matsukura F, Ohno H. Effect of low-temperatureannealing on (Ga,Mn)as trilayer structures. Applied Physics Letters. 2003;82:3020
  25. 25. Linsebigler AL, Lu G, Yates JT Jr. Photocatalysis on TiO2 surfaces: Principles, mechanisms, and selected results. Chemical Reviews. 1995;95:735
  26. 26. Wang R, Hashimoto K, Fujishima A, Chikuni M, Kojima E, Kitamura A, Shimohigoshi M, Watanabe T. Light-induced amphiphilic surfaces. Nature. 1997;388:431
  27. 27. Zhuang J, Rusu CN, Yates T Jr. Adsorption and photooxidation of CH3CN on TiO2. Journal of Physical Chemistry B. 1999;103:6957
  28. 28. Diebold U. The surface science of titanium dioxide. Surface Science Reports. 2003;48:53
  29. 29. Matsumoto YJ, Murakami M, Shono TJ, Hasegawa T, Fukumura T, Kawasaki M, Ahmet P, Chikyow T, Koshihara SY, Koinuma H. Roomtemperature ferromagnetism in transparent transition metal-doped titanium dioxide. Science. 2001;291:854-856
  30. 30. Matsumoto Y, Takahashi R, Murakami M, Koida T, Fan X-J, Hasegawa T, Fukumura T, Kawasaki M, Koshihara S-Y, Koinuma H. Ferromagnetism in Co doped TiO2 rutile thin films grown by laser molecular beam epitaxy. Japanese Journal of Applied Physics. 2001;40:L1204
  31. 31. Shinde SR, Ogale SB, Das Sarma S, Simpson JR, Drew HD, Lofland SE, Lanci C, Buban JP, Browning ND, Kulkarni VN, Higgins J, Sharma RP, Greene RL, Venkatesan T. Ferromagnetism in laser depositedanatase Ti1-xCoxO2-δ films. Physical Review B. 2003;67:115211
  32. 32. Kim DH, Yang JS, Lee KW, Bu SD, Noh TW, Oh S-J, Kim Y-W, Chung J-S, Tanaka H, Lee HY, Kawai T. Formation of co nanoclustersinepitaxial Ti0.96Co0.04O2 thin films and their ferromagnetism. Applied Physics Letters. 2002;81:2421
  33. 33. Yamada Y, Toyosaki H, Tsukazaki A, Fukumura T, Tamura K, Segawa Y, Nakajima K, Aoyama T, Chikyow T, Hasegawa T, Koinuma H, Kawasaki M. Epitaxial growth and physical properties of a room temperature ferromagneticsemiconductor: Anatase phase Ti1-xCoxO2. Journal of Applied Physics. 2004;96:5097
  34. 34. Stampe PA, Kennedy RJ, Xin Y, Parker JS. Investigation of the cobaltdistribution in TiO2:Co thin films. Journal of Applied Physics. 2002;92:7114
  35. 35. Higgins JS, Shinde SR, Ogale SB, Venkatesan T, Greene RL. Hall effect in cobalt-doped TiO2-δ. Physical Review B. 2004;69:073201
  36. 36. Yang HS, Choi J, Craciun V, Singh RK. Ferromagnetism of anatase Ti1–XCoxO2-δ films grown by ultraviolet-assisted pulsed laser deposition. Journal of Applied Physics. 2003;93:7873
  37. 37. Kim J-Y, Park J-H, Park B-G, Noh H-J, Oh S-J, Yang JS, Kim D-H, Bu SD, Noh T-W, Lin H-J, Hsieh H-H, Chen CT. Ferromagnetism induced by clustered co in co-doped anatase TiO2 thin films. Physical Review Letters. 2003;90:017401
  38. 38. Murakami M, Matsumoto Y, Hasegawa T, Ahmet P, Nakajima K, Chikyow T, Ofuchi H, Nakai I, Koinuma H. Cobalt valence states and origins of ferromagnetism in co doped TiO2 rutile thin films. Journal of Applied Physics. 2004;95:5330
  39. 39. Toyosaki H, Fukumura T, Yamada Y, Nakajima K, Chikyow T, Hasegawa T, Koinuma H, Kawasaki M. Anomalous hall effect governed by electron doping in aroom-temperature transparent ferromagnetic semiconductor. Nature Materials. 2004;3:221
  40. 40. Seong NJ, Yoon SG, Cho CR. Effects of co-doping level on themicrostructural and ferromagnetic properties of liquid-delivery metalorganicchemical-vapor-deposited Ti1–xCoxO2 thin films. Applied Physics Letters. 2002;81:4209
  41. 41. Chambers SA, Thevuthasan S, Farrow RFC, Marks RF, Thiele JU, Folks L, Samant MG, Kellock AJ, Ruzycki N, Ederer DL, Diebold U. Epitaxial growth and properties of ferromagnetic co-doped TiO2 anatase. Applied Physics Letters. 2001;79:3467
  42. 42. Soo YL, Kioseoglou G, Kim S, Kao YH, Sujatha DP, Parise J, Gambinoand RJ, Gouma PI. Local environment surrounding magnetic impurity atoms in a structural phase transition of co-doped TiO2 nanocrystal ferromagnetic semiconductors. Applied Physics Letters. 2002;81:655
  43. 43. Calderón MJ, Das Sarma S. Theory of carrier mediated ferromagnetism in dilute magnetic oxides. Annals of Physics. 2007;322:2618
  44. 44. Zhao T, Shinde SR, Ogale SB, Zheng H, Venkatesan T, Ramesh R, Das Sarma S. Electric field effect in diluted magnetic insulator anatase co:__TiO2. Physical Review Letters. 2005;94:126601
  45. 45. Jaffe JE, Drouban TC, Chambers SA. Oxygen vacancies and ferromagnetismin CoxTi1-xO2-x-y. Journal of Applied Physics. 2005;97:073908
  46. 46. Kaminski A, Das Sarma S. Polaron percolation in diluted magneticsemiconductors. Physical Review Letters. 2002;88:247202
  47. 47. http://repositorio.ul.pt/bitstream/10451/1635/11/19491_ulsd_re481_CHAPTER_2.pdf
  48. 48. Tada H, Kiyonaga T, Naya S. Chemical Society Reviews. 2009;38:1849-1858
  49. 49. Vaseem M, Umar A, Hahn YB. American Science Publications. 2010;5:1
  50. 50. Schlamp MC, Peng XG, Alivisatos AP. Journal of Applied Physics. 1997;82:5837
  51. 51. Sundar VC, Lee J, Heine JR, Bawendi MG, Jensen KF. Advanced Materials. 2000;12:1102
  52. 52. Kazes M, Lewis DY, Ebenstein Y, Mokari T, Bannin U. Advanced Materials. 2002;14:317
  53. 53. Britt J, Ferekides C. Applied Physics Letters. 1993;62:2851
  54. 54. Wu YL, Lim CS, Fu S, Tok AIY, Lau HM, Boey FYC, Zeng XT. Nanotechnology. 2007;18:5604
  55. 55. Baruah JM, Narayan J.  Journal of Optics. 2017.https://doi.org/10.1007/s12596-017-0417-y
  56. 56. Makkar M, Viswanatha R. Current Science. 10 APRIL 2017;112(7)
  57. 57. Saha A, Shetty A, Pavan A, Chattopadhyay S, Shibata T, Viswanatha R. Uniform doping in quantum-dots-based dilute magnetic semiconductor. Journal of Physical Chemistry Letters. 2016;7:2420-2428
  58. 58. Pradhan N, Goorskey D, Thessing J, Peng X. An alternative of CdSe nanocrystal emitters: Pure and tunable impurity emissions in ZnSe nanocrystals. Journal of the American Chemical Society. 2005;127:17586-17587
  59. 59. Peng X, Wickham J, Alivisatos A. Kinetics of II–VI and III–V colloidal semiconductor nanocrystal growth: ‘Focusing’ of size distributions. Journal of the American Chemical Society. 1998;120:5343-5344
  60. 60. Sharma P et al. Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO. Nature Materials. 2003;2:673-677
  61. 61. Jana S, Srivastava BB, Jana S, Bose R, Pradhan N. Multifunctional doped semiconductor nanocrystals. Journal of Physical Chemistry Letters. 2012;3:2535-2540
  62. 62. Viswanatha R, Naveh D, Chelikowsky JR, Kronik L, Sarma DD. Magnetic properties of Fe/cu co-doped ZnO nanocrystals. Journal of Physical Chemistry Letters. 2012;3:2009-2014
  63. 63. Sanders G, Musfeldt J, Stanton C. Tuningg-factors of core-shell nanoparticles by controlled positioning of magneticimpurities. Physical Review B. 2016;93:075431
  64. 64. MacKay J, Becker W, Spaek J, Debska U. Temperature and magnetic-field dependence of the Mn2+4T1(4 G) � 6A1(6 S)photoluminescence band in Zn0.5Mn0.5Se. Physical Review B. 1990;42:1743
  65. 65. Viswanatha R, Pietryga JM, Klimov VI, Crooker SA. Spin-polarized Mn2+ emission from Mn-doped colloidal nanocrystals. Physical Review Letters. 2011;107067402
  66. 66. Pandey A, Brovelli S, Viswanatha R, Li L, Pietryga J, Klimov VI, Crooker S. Long-lived photoinduced magnetization in copper-doped ZnSe–CdSe core-shell nanocrystals. Nature Nanotechnology. 2012;7:792-797
  67. 67. Beaulac R, Schneider L, Archer PI, Bacher G, Gamelin DR. Light-induced spontaneous magnetization in doped colloidal quantum dots. Science. 2009;325:973-976
  68. 68. Zheng W, Strouse GF. Involvement of carriers in the size dependent magnetic exchange for Mn : CdSe quantum dots. Journal of American Chemical Society. 2011;133:7482-7489
  69. 69. Ochsenbein ST, Feng Y, Whitaker KM, Badaeva E, Liu WK, Li X, Gamelin DR. Charge-controlled magnetism in colloidal doped semiconductor nanocrystals. Nature Nanotechnology. 2009;4:681-687
  70. 70. Shanker GS, Tandon B, Shibata T, Chattopadhyay S, Nag A. Doping controls plasmonics, electrical conductivity, and carrier-mediated magnetic coupling in Fe and Sncodoped In2O3 nanocrystals: Local structure is the key. Chemistry of Materials. 2015;27:892-900
  71. 71. Tandon B, Yadav A, Nag A. Delocalized electrons mediated magnetic coupling in Mn–Sncodoped In2O3 nanocrystals: Plasmonics shows the way. Chemistry of Materials. 2016;28:3620-3624

Written By

Jejiron Maheswari Baruah and Jyoti Narayan

Submitted: October 10th, 2017 Reviewed: December 20th, 2017 Published: April 4th, 2018