Showing papers on "Magnetic semiconductor published in 2013"
TL;DR: In this article, a two-dimensional diluted magnetic semiconductor (MoS2) is proposed, which is doped by transition metal atoms from the IIIB to VIB groups.
Abstract: Using first-principles calculations, we propose a two-dimensional diluted magnetic semiconductor: monolayer MoS2 doped by transition metals. Doping of transition metal atoms from the IIIB to VIB groups results in nonmagnetic states, since the number of valence electrons is smaller or equal to that of Mo. Doping of atoms from the VIIB to IIB groups becomes energetically less and less favorable. Magnetism is observed for Mn, Fe, Co, Zn, Cd, and Hg doping, while for the other dopants from these groups it is suppressed by Jahn-Teller distortions. Analysis of the binding energies and magnetic properties indicates that (Mo,X)S2 (X = Mn, Fe, Co, and Zn) are promising systems to explore two-dimensional diluted magnetic semiconductors.
487 citations
TL;DR: The first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B) is reported.
Abstract: Recent studies have reported an interesting class of semiconductor materials that bridge the gap between semiconductors and half-metallic ferromagnets. These materials, called spin gapless semiconductors, exhibit a band gap in one of the spin channels and a zero band gap in the other and thus allow for tunable spin transport. Here, we report the first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B). Below 300 K, the compound exhibits nearly temperature-independent conductivity, very low, temperature-independent carrier concentration, and a vanishing Seebeck coefficient. The anomalous Hall effect is comparatively low, which is explained by the symmetry properties of the Berry curvature. Mn(2) CoAl is not only suitable material for room temperature semiconductor spintronics, the robust spin polarization of the spin gapless semiconductors makes it very promising material for spintronics in general.
399 citations
TL;DR: In this article, the electronic and magnetic properties of Mn-doped monolayer MoS were investigated using a combination of first-principles density functional theory (DFT) calculations and Monte Carlo simulations.
Abstract: We investigate the electronic and magnetic properties of Mn-doped monolayer MoS${}_{2}$ using a combination of first-principles density functional theory (DFT) calculations and Monte Carlo simulations. Mn dopants that are substitutionally inserted at Mo sites are shown to couple ferromagnetically via a double-exchange mechanism. This interaction is relatively short ranged, making percolation a key factor in controlling long-range magnetic order. The DFT results are parameterized using an empirical model to facilitate Monte Carlo studies of concentration- and temperature-dependent ordering in these systems, through which we obtain Curie temperatures in excess of room temperature for Mn doping in the range of 10--15$%$. Our studies demonstrate the potential for engineering a new class of atomically thin dilute magnetic semiconductors based on Mn-doped MoS${}_{2}$ monolayers.
399 citations
TL;DR: In this paper, the authors employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type quaternary Heusler compounds, including half-metals, spin-gapless semiconductors, and 9 semiconductor types.
Abstract: We employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type (also known as LiMgPdSb-type) quaternary Heusler compounds. All compounds obey the Slater-Pauling rule with diverse electronic and magnetic properties. 41 compounds are found to be half-metals, 8 spin-gapless semiconductors, and 9 semiconductors. CoVTiAl and CrVTiAl compounds are identified as ferromagnetic and antiferromagnetic semiconductors, respectively, with large energy gaps in both spin directions. All magnetic compounds are expected to have high Curie temperatures making them suitable for spintronics/magnetoelectronics applications.
329 citations
TL;DR: In this article, the long-range ferromagnetism of Mn spins is mediated by an antiferromagnetic (AFM) exchange between the localized Mn $d$ states and the delocalized $p$ states of the S, Se, and Te atoms.
Abstract: We report an investigation of long-range ferromagnetic (FM) ordering in Mn-doped MoS${}_{2}$, MoSe${}_{2}$, MoTe${}_{2}$, and WS${}_{2}$ for Mn concentration less than 5$%$ using density functional theory calculations. The long-range ferromagnetism of Mn spins is mediated by an antiferromagnetic (AFM) exchange between the localized Mn $d$ states and the delocalized $p$ states of the S, Se, and Te atoms. In contrast, transition metals like Fe, Co, and Ni show a FM exchange with the S, Se, and Te atoms, which results in a very weak FM (even slightly AFM) coupling for transition-metal defects with large separations. The Mn substitution at Mo or W sites is energetically favorable, thus making the Mn-doped dichalcogenides promising candidates for two-dimensional dilute magnetic semiconductors.
262 citations
TL;DR: In this paper, the authors employ ab-initio electronic structure calculations to search for spin gapless semiconductors among the inverse Heusler compounds and identify six compounds that exhibit semiconducting behavior concerning the spindown band structure and in the spin-up band structure.
Abstract: We employ ab-initio electronic structure calculations to search for spin gapless semiconductors among the inverse Heusler compounds. The occurrence of this property is not accompanied by a general rule and results are materials specific. The six compounds identified show semiconducting behavior concerning the spin-down band structure and in the spin-up band structure the valence and conduction bands touch each other leading to 100% spin-polarized carriers. Moreover, these six compounds should exhibit also high Curie temperatures and thus are suitable for spintronics applications.
168 citations
TL;DR: In this article, the thermoelectric properties of the carrier-doped chalcopyrite alloys, Cu1-xFe1+xS2 with x = 0.03 and 0.05, and Zn0.03Cu0.97FeS2, were investigated.
Abstract: The chalcopyrite CuFeS2 is a natural magnetic semiconductor, where Fe spins order antiferromagnetically at TN = 853 K. We investigate the thermoelectric properties of the carrier-doped chalcopyrite alloys, Cu1-xFe1+xS2 with x = 0.03 and 0.05, and Zn0.03Cu0.97FeS2. All systems showed characteristic behavior of n-type degenerate semiconductors. The large Seebeck coefficient with a high carrier-density indicates enhanced carrier mass of m* = 3–6m0, where m0 is the electron mass. Consequently, the thermoelectric power factor exceeds 1×10-3 W K-2 m-1 at 400 K. We propose that utilizing magnetic semiconductor can be a new effective strategy to obtain enhanced values of the power factor.
157 citations
TL;DR: The synthesis of a new diluted magnetic semiconductor is reported, which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr( 2)Si(2) (122) structure, which makes them promising for the development of multilayer functional devices.
Abstract: Diluted magnetic semiconductors have received much attention due to their potential applications for spintronics devices. A prototypical system (Ga,Mn)As has been widely studied since the 1990s. The simultaneous spin and charge doping via hetero-valent (Ga(3+),Mn(2+)) substitution, however, resulted in severely limited solubility without availability of bulk specimens. Here we report the synthesis of a new diluted magnetic semiconductor (Ba(1-x)K(x))(Zn(1-y)Mn(y))(2)As(2), which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr(2)Si(2) (122) structure. Holes are doped via (Ba(2+), K(1+)) replacements, while spins via isovalent (Zn(2+),Mn(2+)) substitutions. Bulk samples with x=0.1-0.3 and y=0.05-0.15 exhibit ferromagnetic order with T(C) up to 180 K, which is comparable to the highest T(C) for (Ga,Mn)As and significantly enhanced from T(C) up to 50 K of the '111'-based Li(Zn,Mn)As. Moreover, ferromagnetic (Ba,K)(Zn,Mn)(2)As(2) shares the same 122 crystal structure with semiconducting BaZn(2)As(2), antiferromagnetic BaMn(2)As(2) and superconducting (Ba,K)Fe(2)As(2), which makes them promising for the development of multilayer functional devices.
144 citations
TL;DR: In this paper, the authors proposed the incorporation of half-metallic Heusler alloys grown at high temperatures (>200°C) along with insertion of a MgO tunnel barrier at the ferromagnet/semiconductor interface to minimize magnetic impurity in-diffusion and potentially act as a spin filter.
Abstract: The notion of using electron spins as bits for highly efficient computation coupled with non-volatile data storage has driven an intense international research effort over the past decade. Such an approach, known as spin-based electronics or spintronics, is considered to be a promising alternative to charge-based electronics in future integrated circuit technologies. Many proposed spin-based devices, such as the well-known spin-transistor, require injection of spin polarized currents from ferromagnetic layers into semiconductor channels, where the degree of injected spin polarization is crucial to the overall device performance. Several ferromagnetic Heusler alloys are predicted to be half-metallic, meaning 100% spin-polarized at the Fermi level, and hence considered to be excellent candidates for electrical spin injection. Furthermore, they exhibit high Curie temperatures and close lattice matching to III-V semiconductors. Despite their promise, Heusler alloy/semiconductor heterostructures investigated in the past decade have failed to fulfill the expectation of near perfect spin injection and in certain cases have even demonstrated inferior behavior compared to their elemental ferromagnetic counterparts. To address this problem, a slew of theoretical and experimental work has emerged studying Heusler alloy/semiconductor interface properties. Here, we review the dominant prohibitive materials challenges that have been identified, namely atomic disorder in the Heusler alloy and in-diffusion of magnetic impurities into the semiconductor, and their ensuing detrimental effects on spin injection. To mitigate these effects, we propose the incorporation of half-metallic Heusler alloys grown at high temperatures (>200 °C) along with insertion of a MgO tunnel barrier at the ferromagnet/semiconductor interface to minimize magnetic impurity in-diffusion and potentially act as a spin-filter. By considering evidence from a variety of structural, optical, and electrical studies, we hope to paint a realistic picture of the materials environment encountered by spins upon injection from Heusler alloys into semiconductors. Finally, we review several emerging device paradigms that utilize Heusler alloys as sources of spin polarized electrons.
129 citations
TL;DR: In this paper, structural, optical, vibrational, and magnetic properties of solgel derived Zn1−xNixO (x 0.02, 0.04, and 0.06) nanoparticles were investigated.
Abstract: With a view to study structural, optical, vibrational, and magnetic properties of solgel derived Zn1−xNixO (x = 0.02, 0.04, and 0.06) nanoparticles, systematic investigations have been carried out. The Rietveld refinement of X-ray powder diffraction data revealed a single hexagonal phase with space group P63mc. The secondary phase of NiO appeared only in 6% Ni doped sample. Phonon modes in Ni doped ZnO nanoparticles were studied through Fourier transform infrared measurements. Furthermore, the enhancement in optical band gap with Ni doping from 3.29 to 3.32 eV has been observed through UV-visible spectroscopic analysis. Photoluminescence spectra of Zn1−xNixO show the UV-emission peak showing the blue shift with increase in doping concentration followed by broad visible (blue) emission corresponding to the defect emission whose intensity decreased with increasing Ni concentration. A clear room temperature ferromagnetism is observed in all samples but saturation magnetization decreased with increasing Ni co...
107 citations
TL;DR: In this article, the structure, magnetic, and transport properties of thin films of the Heusler ferrimagnet Mn2CoAl have been investigated for properties related to spin gapless semiconductors.
Abstract: The structure, magnetic, and transport properties of thin films of the Heusler ferrimagnet Mn2CoAl have been investigated for properties related to spin gapless semiconductors. Oriented films were grown by molecular beam epitaxy on GaAs substrates and the structure was found to transform from tetragonal to cubic for increasing annealing temperature. The anomalous Hall resistivity is found to be proportional to the square of the longitudinal resistivity and magnetization expected for a topological Berry curvature origin. A delicate balance of the spin-polarized carrier type when coupled with voltage gate-tuning could significantly impact advanced electronic devices.
TL;DR: In this paper, the magnetic, resistivity and Hall effect measurements on a ferromagnetically ordered 5% Gd low energy implanted ZnO single crystal were reported. But, the results from temperature-dependent magnetization measurements show that the Gd ions do not contribute to the magnetic order; hence, the magnetic ordering is intrinsic.
Abstract: We report the results from magnetic, resistivity, and Hall effect measurements on a ferromagnetically ordered 5% Gd low energy implanted ZnO single crystal. Temperature-dependent magnetization measurements show that the Gd ions do not contribute to the magnetic order; hence, the magnetic order is intrinsic. The electronic transport in the Gd-implanted region is inhomogeneous, and there is a nonlinear Hall resistance. The nonlinear Hall resistance is likely to be a consequence of the inhomogeneous transport and not due to an anomalous Hall effect.
TL;DR: In this article, the exchange interaction between localized magnetic moments mediated by free charge carriers is responsible for a non-monotonic dependence of the low-temperature energy band-gap in dilute magnetic semiconductors.
Abstract: Exchange interaction between localized magnetic moments mediated by free charge carriers is responsible for a non-monotonic dependence of the low-temperature energy band-gap in dilute magnetic semiconductors. We found that in weakly doped Mn-ZnO films, increasing the exchange interaction by increasing the concentration of free charge carriers results in a red-shift of the near-band-edge emission peak at room temperature. An increase of Mn concentration widens the band gap, and a blue-shift prevails. Exchange interaction can be used to tune the room-temperature optical properties of the wide-band gap semiconductor ZnO.
TL;DR: It is argued that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si dangling bond States in the buffer layer exchange coupled to localized states in the hydrogenated graphene layer.
Abstract: We show ferromagnetic properties of hydrogen-functionalized epitaxial graphene on SiC. Ferromagnetism in such a material is not directly evident as it is inherently composed of only nonmagnetic constituents. Our results nevertheless show strong ferromagnetism with a saturation of 0:9� B=hexagon projected area, which cannot be explained by simple magnetic impurities. The ferromagnetism is unique to hydrogenated epitaxial graphene on SiC, where interactions with the interfacial buffer layer play a crucial role. We argue that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si dangling bond states in the buffer layer exchange coupled to localized states in the hydrogenated graphene layer. This forms a quasi-three-dimensional ferromagnet with a Curie temperature higher than 300 K.
TL;DR: In this paper, an alternate method based on mechanical milling was proposed to induce defect-related ferromagnetism in ZnO nanoparticles (NPs) from initial diamagnetic powders.
Abstract: Though ZnO is known as a diamagnetic material, recent studies have revealed that its nanostructures can be ferromagnetic (FM). The FM origin has been ascribed to intrinsic defects. This work shines light on an alternate method based on mechanical milling to induce defect-related ferromagnetism in ZnO nanoparticles (NPs) from initial diamagnetic ZnO powders. Our idea is motivated by the fact that mechanical milling introduces more defects to a ground material. We point out that the FM order increases with increasing the density of defects in ZnO NPs. The experimental results obtained from analyzing X-ray absorption, electron spin resonance, and Raman scattering spectra demonstrate that the ferromagnetism in ZnO NPs is due to intrinsic defects mainly related to oxygen and zinc vacancies. Among these, zinc vacancies play a decisive role in introducing a high FM order in ZnO NPs.
TL;DR: In this article, the electronic and magnetic properties of Cr-doped Cd-Chalcogenides, Cd 1− x Cr x Z (Z=S, Se and Te) for dopant concentration, x = 0.25 and 0.125 are presented in order to search new Dilute Magnetic Semiconductor (DMS) compounds suitable for spintronic applications.
TL;DR: Wang et al. as mentioned in this paper reported the zigzag silicene nanoribbons (ZSiNRs) with asymmetric sp2−sp3 edges are bipolar magnetic semiconductors due to the incorporation of Klein and Zigzag edge states, which can be altered to half-metals with opposite conductive spin channels by p-type and n-type dopings.
Abstract: The nanomaterials with peculiar spintronic characteristics, such as half-metals, spin gapless semiconductors [X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008)], and bipolar magnetic semiconductors [Li et al., Nanoscale 4, 5680 (2012)], play the crucial role in nano-electronics and spintronics. Here, we report the zigzag silicene nanoribbons (ZSiNRs) with asymmetric sp2−sp3 edges are bipolar magnetic semiconductors due to the incorporation of Klein and zigzag edge states. With the bipolar feature, these asymmetric ZSiNRs can be altered to half-metals with opposite conductive spin channels by p-type and n-type dopings. Moreover, the semiconducting properties can also be tailored by the strain, which makes the nanoribbons into spin gapless semiconductors or ferromagnetic metals.
TL;DR: In this paper, the effect of annealing on structural defects and d(0) ferromagnetism in SnO2 nanoparticles prepared by solution combustion method is investigated.
Abstract: The effect of annealing on structural defects and d(0) ferromagnetism in SnO2 nanoparticles prepared by solution combustion method is investigated. The as-synthesized SnO2 nanoparticles were annealed at 400-800 degrees C for 2 h, in ambient conditions. The crystallinity, size, and morphology of the samples were studied using x-ray diffraction and transmission electron microscopy studies. The annealing results in grain growth due to coarsening as well as reduction in oxygen vacancies as confirmed by Raman spectroscopy, photoluminescence spectroscopy, and x-ray photoelectron spectroscopy. All the as synthesized and annealed samples exhibit room temperature ferromagnetism (RTFM) with distinct hysteresis loops and the saturation magnetization as high as similar to 0.02 emu/g in as-synthesized samples. However, the saturation magnetization is drastically reduced with increasing annealing temperature. Further the presence of singly charged oxygen vacancies (V-o(-) signal at g-value 1.99) is confirmed by electron paramagnetic resonance studies, which also diminish with increasing annealing temperature. The observed diminishing RTFM and simultaneous evidences of diminishing O vacancies clearly indicate that RTFM is driven by defects in oxide lattice and confirms primary role of oxygen vacancies in inducing ferromagnetic ordering in metal oxide semiconductors. The study also provides improved fundamental understanding regarding the ambiguity in the origin of intrinsic RTFM in semiconducting metal oxides and projects their technological application in the field of spintronics. (C) 2013 AIP Publishing LLC.
TL;DR: A range of materials that have bipolar spin polarization, including bipolar half metals and bipolar magnetic semiconductors, are reviewed and their potential applications for creating, manipulating, and detecting spin-polarized carriers provide a promising future for electrically controllable spintronics devices.
Abstract: In spintronics, both the charge and spin of the electrons are exploited for information processing. Developing simple methods to manipulate and detect the carriers' spin orientation is among the key issues for spintronics applications. Electrical field has the advantage that it can be easily applied locally in contrast with a conventionally used magnetic field, thus it is more convenient and efficient. Bipolar magnetic materials, characterized by a unique electronic structure where the valence band and conduction band possess opposite spin polarization around the Fermi level, serve as a new class of materials for spintronics through which electrical control of spin-polarization direction can be realized simply by applying a gate voltage. This article reviews a range of materials that have bipolar spin polarization, including bipolar half metals and bipolar magnetic semiconductors, and their potential applications for creating, manipulating, and detecting spin-polarized carriers. These materials provide a promising future for electrically controllable spintronics devices.
TL;DR: In this article, the defects-induced room-temperature ferromagnetism was originated from the surface defects and specifically, from singly occupied oxygen vacancies denoted as F+, by optical and electrical properties measurements as well as positron annihilation analysis.
Abstract: We clarified, in this Letter, that in un-doped ZnO single crystals after thermal annealing in flowing argon, the defects-induced room-temperature ferromagnetism was originated from the surface defects and specifically, from singly occupied oxygen vacancies denoted as F+, by the optical and electrical properties measurements as well as positron annihilation analysis. In addition, a positive linear relationship was observed between the ferromagnetism and the F+ concentration, which is in support with the above clarification.
TL;DR: In this article, the magnetic field dependent magnetoresistance (MR) curve exhibits two distinct regions: the low-field MR which shows a rapid increase in an applied field within 200 Oe and the high-fieldMR which showed a relatively slow increase with the field increasing (more than 200
Abstract: Near room-temperature magnetoresistance (MR) effect in ferromagnetic semiconductor La2NiMnO6 has been reported. The magnetic field dependent MR curve exhibits two distinct regions: the low-field MR which shows a rapid increase in an applied field within 200 Oe and the high-field MR which shows a relatively slow increase with the field increasing (more than 200 Oe). Based on the analyses of magnetic and electronic properties, we suggest that the low-field MR comes from the increased electron tunneling probability accompanied by the alignment of ferromagnetic domains under external field and the high-field MR is due to the suppression of scattering from the spin defects arising from the Ni/Mn antisite disorders.
TL;DR: Both the 2D monolayer MoO3 sheet and the 1D nanoribbons maintain the semiconducting behaviors when exerting axial strain and provide a simple and effective route to tune the magnetic and electronic properties ofMoO3 nanostructures in a wide range and also facilitate the design of MoO2-based nanodevices.
Abstract: Density functional theory computations were performed to examine the electronic and magnetic properties of MoO3 two-dimensional (2D) nanosheets and their derived one-dimensional (1D) nanoribbons (NRs). The pristine 2D MoO3 sheet is a nonmagnetic semiconductor with an indirect band gap, but can be transformed to a magnetic metal when the surface O atoms are saturated by H. Depending on the cutting pattern, the pristine 1D NRs can be indirect band gap nonmagnetic semiconductors, magnetic semiconductors or magnetic metals. The fully hydrogenated NRs are metallic, while the edge-passivated NRs possess the nonmagnetic semiconducting feature, but with narrower band gap values compared to the pristine NRs. Both the 2D monolayer MoO3 sheet and the 1D nanoribbons maintain the semiconducting behaviors when exerting axial strain. These findings provide a simple and effective route to tune the magnetic and electronic properties of MoO3 nanostructures in a wide range and also facilitate the design of MoO3-based nanodevices.
TL;DR: A simple and modified solvothermal method using oxalate precursor, used to synthesize Cd1−xNixO (x = 0.047, 0.102, and 0.163) nanoparticles and their phase structure, morphology, optical and magnetic properties, have been investigated as mentioned in this paper.
Abstract: A simple and modified solvothermal method using oxalate precursor, used to synthesize Cd1−xNixO (x = 0.047, 0.102, and 0.163) nanoparticles and their phase structure, morphology, optical and magnetic properties, have been investigated. X-ray diffraction studies revealed that as-prepared Ni-doped CdO solid solutions are highly crystalline and stabilized in a monophasic cubic CdO structure. X-ray diffraction and ICP-MS studies confirmed the incorporation of Ni2+ in a CdO matrix. The average grain size was found to be 30, 15, and 11 nm, respectively, using transmission electron microscopic studies. High surface area in the range of 118–143 m2/g has been achieved for these solid solutions using the multipoint BET method, which increases on increasing Ni concentration in Cd lattice site. The optical band gap of these solid solutions shows red shift to the undoped CdO. Ni-doped CdO nanoparticles exhibit co-existence of paramagnetism and ferromagnetism.
TL;DR: Li(Zn, Mn)P as mentioned in this paper is a diluted magnetic semiconductor, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn2+ for Zn2+, respectively.
Abstract: We report the discovery of a diluted magnetic semiconductor, Li(Zn,Mn)P, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn2+ for Zn2+, respectively. Isostructural to (Ga,Mn)As, Li(Zn, Mn) P was found to be a p-type ferromagnetic semiconductor with excess lithium providing charge doping. First-principles calculations indicate that excess Li is favored to partially occupy the Zn site, leading to hole doping. Ferromagnetism with Curie temperature up to 34 K is achieved while the system still shows semiconducting transport behavior.
TL;DR: In this article, the effect of Co doping on the electrical and magnetic properties was studied using dielectric spectroscopy and vibrating sample magnetometer (VSM) at room temperature.
Abstract: Nanoparticles of basic composition Sn 1−x Co x O 2 ( x =0.00, 0.01, 0.03, 0.05 and 0.1) were synthesized through the citrate-gel method and were characterized for structural properties using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). XRD analysis of the powder samples sintered at 500 °C for 12 h showed single phase rutile type tetragonal structure and the crystallite size decreased as the cobalt content was increased. FT-IR spectrum displayed various bands that came due to fundamental overtones and combination of O–H, Sn–O and Sn–O–Sn entities. The effect of Co doping on the electrical and magnetic properties was studied using dielectric spectroscopy and vibrating sample magnetometer (VSM) at room temperature. The dielectric parameters ( e , tan δ and σ ac ) show their maximum value for 10% Co doping. The dielectric loss shows anomalous behavior with frequency where it exhibits the Debye relaxation. The variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to the Maxwell–Wagner type of interfacial polarization in general and hopping of charge between Sn 2+ and Sn 4+ as well as between Co 2+ and Co 3+ ions. The complex impedance analysis was used to separate the grain and grain boundary contributions in the system which shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume. Hysteresis loops were observed clearly in M – H curves from 0.01 to 0.1% Co doped SnO 2 samples. The saturation magnetization of the doped samples increased slightly with increase of Co concentration. However pure SnO 2 displayed paramagnetism which vanished at higher values of magnetic field.
TL;DR: In this paper, the authors theoretically investigated the control of the electron-spin polarization in a spin filter by tunalbe δ-doping, where the device and the δdoping can be realized experimentally by depositing a ferromagnetic stripe on top of semiconductor heterostructure and using molecular beam epitaxy or metal-organic chemical-vapor deposition, respectively.
Abstract: We theoretically investigate the control of the electron-spin polarization in a spin filter by a tunalbe δ-doping, where the device and the δ-doping can be realized experimentally by depositing a ferromagnetic stripe on top of semiconductor heterostructure and using molecular beam epitaxy or metal-organic chemical-vapor deposition, respectively. The δ-doping dependent transmission and conductance are numerically calculated for InAs material system. It is shown that both amplitude and sign of electron-spin polarization vary dramatically with the weight and/or the location of the δ-doping. Thus, it is possible to open a new door for effectively manipulating spin-polarized source, and the considered nanostructure can serve as a spin filter with a structurally controllable spin polarization by the δ-doping.
TL;DR: ZnO has long been considered as a promising candidate material for diluted magnetic semiconductors, owing to its theoretically predicted and experimentally observed above-room-temperature ferromagnetism and long spin-coherence time as discussed by the authors.
Abstract: ZnO has long been considered as a promising candidate material for diluted magnetic semiconductors, owing to its theoretically predicted and experimentally observed above-room-temperature ferromagnetism and long spin-coherence time. In this brief perspective, recent progress in ZnO diluted magnetic semiconductors is reviewed with particular focus on three topics: (1) spin coherence in ZnO; (2) free-carrier type and concentration-dependent magnetic properties in ZnO; and (3) ferromagnetism in undoped and non-transition-metal-doped ZnO. Finally, current status and possible potential direction of research on ZnO diluted magnetic semiconductors are summarized in the concluding remarks.
TL;DR: In this article, the authors focus on the hard part of the x-ray spectrum (above 3 keV) in order to demonstrate a powerful element and orbital-selective characterization tool in the study of bulk electronic structure.
Abstract: This review aims to introduce the x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS) techniques to the materials scientist working with magnetic semiconductors (e.g. semiconductors doped with 3d transition metals) for applications in the field of spin-electronics. We focus our attention on the hard part of the x-ray spectrum (above 3 keV) in order to demonstrate a powerful element- and orbital-selective characterization tool in the study of bulk electronic structure. XES and RIXS are photon-in/photon-out second order optical processes described by the Kramers-Heisenberg formula. Nowadays, the availability of third generation synchrotron radiation sources permits applying such techniques also to dilute materials, opening the way for a detailed atomic characterization of impurity-driven materials. We present the K{\beta} XES as a tool to study the occupied valence states (directly, via valence-to-core transitions) and to probe the local spin angular momentum (indirectly, via intra-atomic exchange interaction). The spin sensitivity is employed, in turn, to study the spin-polarized unoccupied states. Finally, the combination of RIXS with magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard magnetic characterization tools.
TL;DR: In this paper, an alternative spin filter material based on the quaternary Heusler compounds CoVXAl (X = Ti, Zr, Hf) was proposed.
Abstract: Using ab-initio electronic structure calculations, we propose an alternative class of spin filter materials (SFMs) based on the quaternary Heusler compounds CoVXAl (X = Ti, Zr, Hf). We show that the p-d hybridization leads to the formation of the ferromagnetic band gap with a moderate exchange splitting ΔEex and a Curie temperature TC well above the room temperature. We find that all three compounds are thermodynamically and magnetically stable. Combination of high TC value together with moderate exchange splitting, as well as crystal structures compatible to the existing semiconductors and metals, makes these compounds promising candidates to find applications as SFMs in spintronics devices.
TL;DR: In this paper, the interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganized-doped silicon clusters.
Abstract: The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with 3$d$ electron delocalization and a quenching of high-spin states. For all geometric structures investigated, we find a correlation of the magnetic moment with the manganese coordination number and nearest-neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and therefore react very sensitively to changes in the local geometry. The results indicate that high-spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion.