Diluted Magnetic Semiconductors Materials Research Articles

New spin-electronics compositions: Large ferromagnetic order of BaSn0.98-xFe0.02CuxO3 (x = 0.02, 0.04, 0.06) semiconductor

Inducing robust ferromagnetic order in dilute magnetic semiconductor materials is an essential topic for spin-based electronics devices. Herein, the escalating concentration of nonmagnetic Cu ions was employed to strongly reinforce the room temperature ferromagnetism of 2% Fe doped BaSnO3 structure. BaSn0.98-xFe0.02CuxO3 (x = 0.02, 0.04 or 0.06) compositions were prepared by adapted sol gel method. In all compositions, pure single phase with cubic structure of BaSnO3 was identified by the X-ray diffraction (XRD) technique. Pure BaSnO3 gives a band gap energy of 3.25 eV which red shifted to 3.1, 3.12 and 3.13 eV after incorporation of (2% Fe, 2% Cu), (2% Fe, 4% Cu) and (2% Fe, 6% Cu) ions, respectively. The scanning electron microscope (SEM) images reflects that the Fe/Cu blends obstruct the grains growth of BaSnO3 and also influenced on the particles shape and porosity. The energy dispersive X-ray (EDX) maps confirmed the homogenous spatial distribution of Fe and Cu in the codoped BaSnO3 structure. The X-ray photoelectron spectroscopy (XPS) results of BaSn0.92Fe0.02Cu0.06O3 prove that Ba, Sn, O, Fe and Cu elements possess the oxidation states of +2, +4, −2, +3 and +1/+2, respectively. The magnetic performance of BaSnO3 structure exhibits a minor ferromagnetic loop with measured coercivity (Hc) of 330 Oe, magnetization (Ms) of 0.0023 emu/g and retentivity of 0.00077 emu/g. Interestingly, the addition of 6 wt% Cu (nonmagnetic dopant) plus 2 wt% Fe (magnetic dopant) strongly boosts the saturation magnetization value of BaSnO3 to 1.85 emu/g. The results open the door to tune the ferromagnetic order of BaSnO3 using nonmagnetic dopant to avoid the formation of magnetic impurities. The F-center exchange interaction and the bound magnetic polarons model were used to explain the measured room temperature ferromagnetism.

Magnetic coupling interaction-related photoluminescence behaviors in all-inorganic manganese chloride perovskites

Manganese halides, as dilute magnetic semiconductor materials, have magnetic coupling interactions that play an essential role in their photoluminescence (PL); however, such interactions remain controversial. AMnCl3 (AMC, A = K, Rb, and Cs) and their hydrates AMnCl3·2H2O (AMCH, A = K, Rb, and Cs) are both in the ABX3 configuration but exhibit a wide variety of structures with different connectivity types and dimensions. Their magnetic coupling interaction has been demonstrated. However, few studies have systematically investigated the PL in conjunction with the magnetic coupling interaction over these chloride compounds. In this paper, the effect of the magnetic coupling interaction on AMC and AMCH PL is mainly revealed by temperature-dependent PL spectra and lifetimes. The MnX6 (X6 = Cl4(H2O)2 or Cl6) cluster connection types affect the Mn2+–Mn2+ distances. The magnetic coupling interaction between MnX6 octahedrons affects the radiative transitions of manganese chlorides, which is influenced by the Mn2+–Mn2+ distance, local symmetry, and water ligand. The Mn2+–Mn2+ distance and the magnetic coupling interaction also affect their lifetimes. Variations in magnetic coupling interactions can shift emission wavelength, especially dual-emissions and near-infrared (NIR) emission at lower temperatures while A+ = K+. This work helps researchers understand the optical process of Mn2+ ions in different manganese compounds and provides new insights into the design of tailored Mn2+ ion phosphors.

Evaluating potential of Cr-doped indium oxide nanoparticles as a DMS material

ABSTRACT Cr-doped In2O3 nanoparticles have been prepared via combustion method. Glycine fuel was used for the synthesis. The prepared compounds were evaluated for their potential as a dilute magnetic semiconductor (DMS) by studying their magnetic properties. X-ray diffraction (XRD) pattern was studied to identify the crystal structure of pristine and doped In2O3 compounds. Morphology and particle size of the compounds have been estimated using transmission electron microscope (TEM). Valence state of the elements was found out by making use of X-ray photoelectron spectroscopy (XPS) technique. Electrical resistivity has been measured which displayed higher resistance value for doped samples. Magnetisation studied with vibrating sample magnetometer (VSM) at room temperature displayed weak ferromagnetism in the doped samples. The measurements at 50 K displayed antiferromagnetic/paramagnetic alignment. The importance of preparative method, nano-size, room-temperature defects and oxygen vacancies in regulating magnetism in DMS has been discussed.

Recent progress in diluted ferromagnetism for spintronic application

With the continuous in-depth research of spintronics, the manufacture of high-performance magnetic random access memory devices and electronic devices that are more energy-efficient and generate less heat has received extensive attention. The traditional ferromagnet TbMnO3 is basically Tc at room temperature, which seriously limits its application. Since the discovery of diluted magnetic semiconductor materials at room temperature, such as AlNTiO2, ZnO, SnO2, etc., they have received increasing attention. Although these dopants can form ferromagnetism above-room temperature, the ferromagnetic mechanism and ferromagnetic properties are different. In this regard, we reviewed the current progress in the research on above room temperature dilute magnetic semiconductor materials; discussed the ferromagnetic mechanism of dilute magnetic semiconductors; summarized the problems and challenges, and advantages and disadvantages of different kinds of dilute magnetic semiconductor materials used in new memory devices; and prospected the application potential of spintronic devices.

Transition metals doped (3,3) armchair boron nitride nanosheet as dilute magnetic semiconductors materials for the spintronic application

AbstractMagnetic 2D materials have attracted considerable attention for their significant potential application in spintronic. In this work, the effect of substitutional doping of 3d‐transition metals such as Co, Cr, Mn, and Fe on the magnetic and electronic properties of boron nitride nanosheet (BNNS) was studied based on the spin‐polarized density functional theory. The results revealed that the non‐magnetic and semiconducting behavior of BNNS can be altered by magnetically active dopants. The spin‐polarized density of states suggests that pure BNNS is a nonmagnetic semiconductor with a direct bandgap while transition metals doped BNNS are dilute magnetic semiconductors or half metals (HM). Co doping shows the most stable ferromagnetic phases in the nanosheet. A pair of Mn and Co atoms doped BNNS in edge structure show HM property with 100% spin polarization and seem to be good candidates for spintronic applications and especially as spin filter devices and spin current injectors.

Transition metal-doped chalcogenide perovskite magnetic semiconductor [formula omitted

Diluted magnetic semiconductors (DMSs) are an important type of materials for spintronic applications. Conventional DMSs are typically based on transition metal doped III-V and II-VI materials such as GaAs and CdSe. In this work, we show that a new DMS material can be realized by transition metal doping in BaZrS3, a prototypical chalcogenide perovskite semiconductor. Mn and Fe elements are doped into the BaZrS3 lattice with a concentration of up to 5%. In particular, Fe-doped BaZrS3 exhibits room temperature ferromagnetism.

Theoretical investigation on the magnetic properties of Cr2Zn10Se12 and C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters

To search for stable structural units of low dimensional dilute magnetic semiconductor materials, Cr-doped and C/N co-doped Zn12Se12 clusters were investigated with first principle all electron calculations. In geometry-optimized Cr2Zn10Se12 nanoclusters, two Cr atoms substituted the nearest Zn atom sites in the rhombus part. Energy analysis indicated that the ground state of Cr2Zn10Se12 nanoclusters tends to be a weak ferromagnetic coupling state originating from the electron hybridization of the Cr-3d, Cr-4s and Se-4p orbitals. In C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters, the C/N atoms prefer to occupy the Se atom sites to form Cr-C-Cr/Cr-N-Cr bonding. The ground state tends to be a slightly stronger ferromagnetic coupling state, with Cr-3d and C/N-2p orbitals being the main contributors to the magnetism of the nanoclusters. With the introduction of C/N co-doped atoms, the strong electron hybridization among C/N-2p, Cr-3d and Cr-4s orbitals contributed to the enhanced stability of ferromagnetic ground state. For all the Cr2Zn10Se12 and C/N co-doped Cr2Zn10CSe11/Cr2Zn10NSe11 nanoclusters, hole-mediated ferromagnetic coupling between Cr atoms was found to improve the ferromagnetic stability, which may provide some guidance for the exploration of new materials.

Effects of magnetic impurity concentration and hole carriers on ferromagnetic stability of Li(ZnCr)As and Li(ZnCrCu)As

First-principles calculations were performed to study electronic structure and magnetic properties of Li(ZnCr)As and Li(ZnCrCu)As. The ground state of Li(ZnCr)As was ferromagnetism. To enhance the ferromagnetic stability of the doping system, two methods were proposed and the exchange mechanism was analyzed. More Cr impurities increased the energy gain and decreased p-d hybridization, contributing to the double-exchange interaction and thus promoting ferromagnetic stability of Li(ZnCr)As. By substituting Zn(3d104s2) with Cu(3d104s1), additional hole carriers were introduced and the ferromagnetism was more stable than that in the single Cr doping case. The ferromagnetism of Li(ZnCrCu)As system was further stabilized with the increase of hole carrier concentration. The Li32(Zn22Cr8Cu2)As32 configuration showed the strongest ferromagnetic stability. Therefore, it was possible to fabricate a new type of dilute magnetic semiconductor material with high ferromagnetic stability by adjusting the concentration of Cr impurity and additional hole carriers.

Structural Quality and Magnetotransport Properties of Epitaxial Layers of the (Ga,Mn)(Bi,As) Dilute Magnetic Semiconductor.

Structural analysis of epitaxial layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor (DMS), together with investigations of their magnetotransport properties, has been thoroughly performed. The obtained results are compared with those for the reference (Ga,Mn)As layers, grown under similar conditions, with the aim to reveal an impact of Bi incorporation on the properties of this DMS material. Incorporation of Bi into GaAs strongly enhances the spin-orbit coupling strength in this semiconductor, and the same has been expected for the (Ga,Mn)(Bi,As) alloy. In turn, importantly for specific spintronic applications, strong spin-orbit coupling in ferromagnetic systems opens a possibility of directly controlling the direction of magnetization by the electric current. Our investigations, performed with high-resolution X-ray diffractometry and transmission electron microscopy, demonstrate that the (Ga,Mn)(Bi,As) layers of high structural quality and smooth interfaces can be grown by means of the low-temperature molecular-beam epitaxy method, despite a large difference between the sizes of Bi and As atoms. Depending on the applied buffer layer, the DMS layers can be grown under either compressive or tensile misfit strain, which influences their magnetic properties. It is shown that even small 1% Bi content in the layers strongly affects their magnetoelectric properties, such as the coercive field and anisotropic magnetoresistance.

High-TC Ferromagnetic Semiconductors: Fake or Fact?

The long lasting interest in diluted magnetic semiconductors (DMS) relies on the combination of fundamental science and the potential for spintronics applications. Despite the large body of experimental and theoretical studies carried out in the past decades, there are ongoing controversies about high-TC ferromagnetic DMS. This paper summarizes the results of the few investigations performed by inelastic neutron scattering, which provides key information for some of the open questions. Emphasis is led on a complete study of the compound MnxGa1 – xN, as well as on novel DMS materials for which the spin injection is decoupled from carrier doping.

Influence of Mg2+ ion on the optical and magnetic properties of TiO2 nanostructures: A key role of oxygen vacancy

Over the years, oxide based dilute magnetic semiconductor (DMS) materials have been of great interest due to their potential use in spintronic devices. Among several oxide based DMS materials, TiO2 nanoparticles (NPs) have been considered largely due to their interesting optical and magnetic properties. The effect of Mg doping on intrinsic defect formation (oxygen vacancy) was investigated by UV–vis and PL spectroscopy studies. In particular, 5% Mg-doped TiO2 has promising photocatalytic activity for the degradation of methylene blue (MB) and 4-nitrophenol (4-NP) over the pure and other Mg-doped TiO2 samples. This noteworthy enhanced photocatalytic activity could be attributed to both the effective separation of charge carrier and the strong light absorption ability, resulting from the incorporation of Mg into TiO2 lattice. As compared to pure TiO2 sample, Mg doped TiO2 samples display a remarked increase in saturation magnetization (Ms). Therefore, the combination of PL and magnetic measurements shows the increase of oxygen vacancy due to the Mg doping which plays a key role in the optical and magnetic performances of the TiO2 NPs.

Anomalous critical point behavior in dilute magnetic semiconductor (Ca,Na)(Zn,Mn)2Sb2

In this paper we report successful synthesis and magnetic properties of (Ca,Na)(Zn,Mn)2Sb2 as a new ferromagnetic dilute magnetic semiconductor (DMS). In this DMS material the concentration of magnetic moments can be controlled independently from the concentration of electric charge carriers that are required for mediating magnetic interactions between these moments. This feature allows us to separately investigate the effect of carriers and of spins on the ferromagnetic properties of this new DMS alloy, and particularly of the critical ferromagnetic behavior. We use modified Arrott plot technique to establish critical exponents b, g, and d of this alloy. We find that at low Mn concentrations (< 10 at.%), it is governed by short-range 3D-Ising behavior, with experimental values of b, g, and d very close to theoretical 3D-Ising values of 0.325, 1.24, and 4.815. However, as the Mn concentration increases, this DMS material exhibits a mixed-phase behavior, with g retaining its 3D-Ising characteristics, but b crossing over to longer-range mean-field behavior.

A substantial increase of Curie temperature in a new type of diluted magnetic semiconductors via effects of chemical pressure

Chemical pressure is an effective method to tune physical properties, particularly for diluted magnetic semiconductors (DMSs) of which ferromagnetic ordering is mediated by charge carriers. Via substitution of smaller Ca for larger Sr, we introduce chemical pressure on (Sr,Na)(Cd,Mn)2As2 to fabricate a new DMS material (Ca,Na)(Cd,Mn)2As2. Carriers and spins are introduced by substitutions of (Ca,Na) and (Cd,Mn), respectively. The unit cell volume reduces by 6.2% after complete substitution of Ca for Sr, suggesting a subsistent chemical pressure. Importantly, the local geometry of the [Cd/MnAs4] tetrahedron is optimized via chemical compression that increases the Mn–As hybridization leading to enhanced ferromagnetic interactions. As a result, the maximum Curie temperature (TC) is increased by about 50% while the maximum saturation moment increases by over 100% from (Sr,Na)(Cd,Mn)2As2 to (Ca,Na)(Cd,Mn)2As2. The chemical pressure estimated from the equation of state is equal to an external physical pressure of 3.6 GPa.

GaN-Based Dilute Magnetic Semiconductors for Room Temperature Neuromorphic and Quantum Computing

Neuromorphic computing and quantum computing are attracting more research attention in recent years. Neuromorphic computing mimic the quantum decoherence for neuron firing and the microtubule processes, and artificially recreating the highly parallel computing architecture of the mammalian brain. Quantum computing is also of great interest for next generation of micro- and nano-electronic devices with enhanced functionalities, which involves the mathematical analysis, algorithmic manipulation, storage, and transmission of the fundamental unit of quantum information, the qubit. However, most of the current quantum computing and neuromorphic computing systems operate at cryogenic temperatures to avoid thermal activation, which limits their wide application. Spintronic devices, exploiting electron spin as a further degree of freedom in addition to the electronic charge, have shown to be promising for quantum information processing and modeling brain-like systems, realizing device-level components for quantum computing and neuromorphic computing applications. In addition, wide bandgap dilute magnetic semiconductors (DMS) have the potential for room temperature (RT) spintronic applications. Gallium nitride (GaN) based DMS are promising materials for spintronic applications due to their theoretically predicted and experimentally observed ferromagnetic properties at RT [1]. In this work, MOCVD-grown Gd-doped GaN showed ferromagnetic hysteresis in vibrating sample magnetometry measurement and Anomalous Hall Effect (AHE) measurement at room temperature. AHE measurement of samples with different carrier densities showed a superlinear relation between anomalous Hall conductivity σAHE and lateral conductivity σxx, σAHE∝σxx1.78 , which indicates the mechanism for the ferromagnetism is intrinsic and likely mediated by free carriers [2], which is conducive for spintronic applications. However, the ferromagnetism is only observed in GaGdN grown using a (TMHD)3Gd precursor, which contains oxygen in its organic ligand that appears to be incorporated into the GaGdN. The role of oxygen in the ferromagnetic properties was predicted in density functional theory calculations, which show that elements such as oxygen and carbon, when incorporated into GaGdN could result in p-d hybridization of the p-orbitals of oxygen or carbon with the d-orbitals of Gd; oxygen or carbon could introduce deep localized states close to the Fermi level in GaGdN that couple with Gd states to render ferromagnetism [3,4]. In order to experimentally examine the role of oxygen or carbon in the ferromagnetic properties of GaGdN, oxygen and carbon are implanted in GaGdN originally grown using a Cp3Gd precursor that does not contain oxygen. As-grown GaGdN from Cp3Gd source, which does not contain O, is not ferromagnetic but post-implantation with O or C does result in ferromagnetism. X-ray diffraction of the implanted GaGdN samples exhibits good crystal quality, and peak shifts as compared to the GaGdN before implantation showing signs of O or C incorporation. Annealing the implanted GaGdN activates the dopant, improves the crystal quality, and shows clear signs of AHE. These results show that oxygen or carbon could have a significant role in rendering the intrinsic and potentially free carrier-mediated ferromagnetism in GaGdN at RT. A better understanding of the mechanism for RT ferromagnetism will enable these DMS materials to build spintronic devices, such as memristive, spin-transfer torque, and non-volatile memory spintronic devices have tremendous applications in neuromorphic computing and quantum computing applications. References Kane, S. Gupta and I. Ferguson, “Transition metal and rare earth doping in GaN”, Woodhead publishing, (2016).Saravade, C. Ferguson, A. Ghods, C. Zhou, and I. Ferguson, MRS Adv. 3 (3), p. 159, (2018).Liu, X. Yi, J. Wang, J. Kang, A. Melton, Y. Shi, N. Lu, J. Wang, J. Li, and I. Ferguson, Appl. Phys. Lett. 100 (23), 232408, (2012).Xie, H. Xing, Y. Zeng, Y. Liang, Y. Huang and X. Chen, AIP Advances 7, 115003, (2017).

Magnetic impurity bands in Ga1−xMnxS : Towards understanding the anomalous spin-glass transition

We report on the magnetic and electronic properties of single-crystalline ${\mathrm{Ga}}_{0.91}{\mathrm{Mn}}_{0.09}\mathrm{S}$, which is a quasi-two-dimensional diluted magnetic semiconductor (DMS). Through an analysis of magnetization data, we show the existence of an anomalously high spin-glass transition temperature at 11.2 K. Using density functional theory (DFT), we characterize the properties contributing to the spin-glass transition through an examination of the electronic and magnetic properties for ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{S}$ with $x$ varying from 0.00 to 0.18 by randomly substituting Mn atoms into the gallium (Ga) lattice sites. We show that the presence of magnetic atoms produces impurity bands in the electronic structure, where an analysis of the density of states shows an increase in magnetic impurity bands at the Fermi level that lowers the semiconducting gap and is consistent with diluted magnetic semiconductors. Furthermore, this indicates that the spin-glass transition in ${\mathrm{Ga}}_{0.91}{\mathrm{Mn}}_{0.09}\mathrm{S}$ is similar to other DMS materials, where the primary mechanism is likely through magnetic exchange. However, the increased electron density in the system with Mn doping could explain the anomalously higher spin-glass transition temperature in ${\mathrm{Ga}}_{0.91}{\mathrm{Mn}}_{0.09}\mathrm{S}$. In comparison with the substantially lower transition temperatures in related II-VI based systems (i.e., ${\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{Mn}{}_{x}\mathrm{Te}$), the high transition temperature is associated with more metallic spin-glass systems that interact through RKKY exchange, which leads to the conclusion that there may be a combination of interactions occurring in these systems. Further measurements on the other substitution percentages will hopefully clarify these interactions.

Magnetic interactions in a proposed diluted magnetic semiconductor (Ba1−xKx)(Zn1−yMny)2P2**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0302903), the National Natural Science Foundation of China (Grant Nos. 11774422 and 11774424), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant Nos. 14XNLQ03 and 16XNLQ01).

By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn2P2-based diluted magnetic semiconductor (DMS). For a typical compound Ba(Zn0.944Mn0.056)2P2 with only spin doping, due to the superexchange interaction between Mn atoms and the lack of itinerant carriers, the short-range antiferromagnetic coupling dominates. Partially substituting K atoms for Ba atoms, which introduces itinerant hole carriers into the p orbitals of P atoms so as to link distant Mn moments with the spin-polarized hole carriers via the p–d hybridization between P and Mn atoms, is very crucial for the appearance of ferromagnetism in the compound. Furthermore, applying hydrostatic pressure first enhances and then decreases the ferromagnetic coupling in (Ba0.75K0.25)(Zn0.944Mn0.056)2P2 at a turning point around 15 GPa, which results from the combined effects of the pressure-induced variations of electron delocalization and p–d hybridization. Compared with the BaZn2As2-based DMS, the substitution of P for As can modulate the magnetic coupling effectively. Both the results for BaZn2P2-based and BaZn2As2-based DMSs demonstrate that the robust antiferromagnetic (AFM) coupling between the nearest Mn–Mn pairs bridged by anions is harmful to improving the performance of these II–II–V based DMS materials.

Lanthanide atom substitutionally doped blue phosphorene: electronic and magnetic behaviors.

The structure, energy, electronic and magnetic properties of lanthanide (La, Ce, Pr, Nd, Pm, Eu and Gd) doped blue phosphorene are systematically investigated by using the GGA+U method. The calculated results show that the semi-metallic or dilute magnetic semiconductor characteristics can be achieved by substitutional doping of lanthanide atoms in blue phosphorene. From La- to Gd-doped blue phosphorene, the calculated spin magnetic moments are respectively 0.0, 1.0, 2.0, 3.0, 4.0, 8.0 and 7.0 μB, which are generally proportional to the number of the spin-parallel 4f electrons in dopants. The spin charge density and Bader charge analysis indicate that the magnetic moments of the lanthanide atom doped systems mainly originate from the lanthanide atoms. Specifically, the Pr-doped system has a magnetocrystalline anisotropy energy (MAE) of up to 66.68 meV with the easy axis parallel to the blue phosphorene plane, and the MAE could be enhanced to 103.51 meV by applying an electric field. The Pr-, Nd-, Pm- and Gd-doped blue phosphorenes have dilute magnetic semiconductor properties, while Ce- and Eu-doped blue phosphorenes exhibit half-metallic behavior. Interestingly, the La, Pr and Nd atom doping can all lead to an indirect-to-direct band gap transition. This study indicates that lanthanide-doped blue phosphorene could be a novel dilute magnetic semiconductor material applied in spintronics and magnetic storage devices.

Defect mediated mechanism in undoped, Cu and Zn-doped TiO2 nanocrystals for tailoring the band gap and magnetic properties.

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol–gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5–15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti3+, Cu2+, Cu+ and Zn2+ in Cu and Zn-doped TiO2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results.

Volume and Concentration Scaling of Magnetism in Dilute Magnetic Semiconductor Quantum Dots

Investigation of the magnetism of dilute magnetic semiconductors (DMSs) by changing particle dimensionality and doping concentration and its complete understanding is a major step toward their application in multifunctional devices. The importance of effects, such as magnetization reversal with size and magnetic invariance with respect to doping concentration for an appropriate functioning of DMS systems, is empirically well-known. However, explicit demonstration of these effects, specifically in nanomaterials, has so far not been studied mainly due to the lack of synthetic handle. In this work, we have demonstrated the prerequisites of DMS materials by isolating origins of magnetism arising due to clustering of magnetic dopant ions as well as sp–d exchange interaction with the host. We have studied magnetism with varying concentrations of dopant ions and have shown that the magnetism arising due to exchange interaction with the host is invariant up to 10% doping concentration, demonstrating the concentra...

Understanding ferromagnetism in C-doped CdS: Monte Carlo simulation

Room-temperature ferromagnetism of diluted magnetic semiconductors (DMSs) doped with light elements has been extensively investigated for potential applications in spintronic devices. Indeed, the mechanism underlying ferromagnetism in DMSs of low concentrations has been studied from both theoretical and experimental perspectives. Theoretically, first-principles calculation and Monte Carlo (MC) simulation were combined together to study electronic and magnetic properties of DMSs. The Curie temperature of DMSs has been usually estimated from Monte Carlo simulation. In particular, MC simulations use both continuous and discrete spin models to describe the spin state in the ferromagnetic phase of DMSs. Nevertheless, which of the two models is the more appropriate is unclear. To clarify further this issue of ”continuous versus discrete” spin model in DMS materials, we have performed a large-scale MC simulation for C-doped CdS material. The discrete spin model sets the ferromagnetic phase transition below room-temperature whereas the continuous spin model sets this transition at rather low temperatures. The discrete spin model is found to describe more appropriately the spin state of C atoms in the C-doped CdS.