Double Covalency Factors and DoubleξModel in Study on Optical and Magnetic Properties of Diluted Magnetic Semiconductors ZnX∶Co~ 2+

The optical absorption spectra of the covalent crystals ZnX(X=S,Se) doped with Co 2+ are studied using the double covalency factors,which considers the anisotropic distortion of e g and t 2g orbits for d electron.When the paramagnetic g factor is calculated,the contributions of the spin orbit coupling from the ligand ions are taken into account besides that from the central ion,which is the double ξ model.The calculated results indicate that the theoretical values coincide with the experimental values very well.This suggests that the method presented in this paper could be more valid to some strongly covalent crystals.

Magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

A series of Mn-doped ZnO films have been prepared in different sputtering plasmas by using the inductively coupled plasma enhanced physical vapour deposition. The films show paramagnetic behaviour when they are deposited in an argon plasma. The Hall measurement indicates that ferromagnetism cannot be realized by increasing the electron concentration. However, the room-temperature ferromagnetism is obtained when the films are deposited in a mixed argon-nitrogen plasma. The first-principles calculations reveal that antiferromagnetic ordering is favoured in the case of the substitution of Mn^2＋ for Zn^2＋ without additional acceptor doping. The substitution of N for O （NO^-） is necessary to induce ferromagnetic couplings in the Zn-Mn-O system. The hybridization between N 2p and Mn 3d provides an empty orbit around the Fermi level. The hopping of Mn 3d electrons through the empty orbit can induce the ferromagnetic coupling. The ferromagnetism in the N-doped Zn-Mn-O system possibly originates from the charge transfer between Mn^2＋ and Mn^3＋ via NO^-, The key factor is the empty orbit provided by substituting N for O, rather than the conductivity type or the carrier concentration.

Theoretical prediction and experimental realization of transition metal doped rutiles as diluted magnetic semiconductors

First principle calculations have been performed to study the electron structures and magnetic properties of transition metal doped ruilles in order to predict room temperature diluted magnetic semiconductors. Different doping configurailons have been calculated to find the preferred doping site. The ground state energies of both FM and AFM states have been calculated to study the magnetic coupling between the dopants. The calculation results show the Co doped mutile has a Curie temperature of 1438 K. Co doped mille films have been prepared on Si substrate by magnetron sputtering. X-ray diffraction results show that the deposited film is ruille. Hysteresis loop curves measured by vibration sample magnetization show that the film is ferromagnetic at root temperature.

Structural stability at high pressure, electronic, and magnetic properties of BaFZnAs：A new candidate of host material of diluted magnetic semiconductors

The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized.Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor.

First-Principles Studies the Lattice Constants and the Electronic Structures of Diluted Magnetic Semiconductors (In,Mn)As

Lattice constants and electronic structures of diluted magnetic semiconductors （ In, Mn ） As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied （ x = 1/2, 1/4, 1/8）. The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown.

A Green’s function model for ferromagnetism and spin excitations of (Ga, Mn)As diluted magnetic semiconductors

We study （Ga, Mn）As diluted magnetic semiconductors in terms of the Ruderman-Kittel-Kasuya-Yosida quantum spin model in Green＇s function approach. Random distributions of the magnetic atoms are treated by using an analytical average of magnetic configurations. Average magnetic moments and spin excitation spectra as functions of temperature can be obtained by solving self-consistent equations, and the Curie temperature TC is given explicitly. Tc is proportional to magnetic atomic concentration, and there exists a maximum for Tc as a function of carrier concentration. Applied to （Ga, Mn）As, the theoretical results are consistent with experiment and the experimental TC can be obtained with reasonable parameters. This modelling can also be applied to other diluted magnetic semiconductors.

Regulating the dopant clustering in LiZnAs-based diluted magnetic semiconductor

Tuning of the magnetic interaction plays the vital role in reducing the clustering of magnetic dopant in diluted magnetic semiconductors(DMS).Due to the not well understood magnetic mechanism and the interplay between different magnetic mechanisms,no efficient and universal tuning strategy is proposed at present.Here,the magnetic interactions and formation energies of isovalent-doped(Mn) and aliovalent(Cr)-doped LiZnAs are studied based on density functional theory(DFT).It is found that the dopant–dopant distance-dependent magnetic interaction is highly sensitive to the carrier concentration and carrier type and can only be explained by the interplay between two magnetic mechanisms,i.e.,superexchange and Zener’s p–d exchange model.Thus,the magnetic behavior and clustering of magnetic dopant can be tuned by the interplay between two magnetic mechanisms.The insensitivity of the tuning effect to U parameter suggests that our strategy could be universal to other DMS.

First-Principle Study on the Electronic Structure and Optical Property of New Diluted Magnetic Semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO

The band structure,DOSs,and optical properties of(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO,including dielectric function,absorption function,reflection function,and energy loss spectrum were studied by using the first-principles calculation.The calculation results indicate that(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO is a direct bandgap semiconductor with a bandgap of 1.1 eV.The Fermi surface is asymmetric and exhibits spin splitting phenomenon.The new type of dilute magnetic semiconductor(Y_(0.75)Ca_(0.25))(Cu_(0.75)Mn_(0.25))SO exhibits significant light loss around 70 eV,with light reflection gradually increasing after 30 eV,and light absorption mainly occurring around 8-30 eV.These results also provide a basis for the discovery of more types of 1111 phase new dilute magnetic semiconductors in the future.

First principles study on the structural, electronic and optical properties of diluted magnetic semiconductors Zn1-xCoxX （X=S, Se, Te）

The electronic and optical properties of zincblende ZnX（X=S, Se, Te） and ZnX：Co are studied from density functional theory （DFT） based first principles calculations. The local crystal structure changes around the Co atoms in the lattice are studied after Co atoms are doped. It is shown that the Co-doped materials have smaller lattice constant （about 0.6%-0.9%）. This is mainly due to the shortened Co-X bond length. The （partial） density of states （DOS） is calculated and differences between the pure and doped materials are studied. Results show that for the Co-doped materials, the valence bands are moving upward due to the existence of Co 3d electron states while the conductance bands are moving downward due to the reduced lattice constants. This results in the narrowed band gap of the doped materials. The complex dielectric indices and the absorption coefficients are calculated to examine the influences of the Co atoms on the optical properties. Results show that for the Co-doped materials, the absorption peaks in the high wavelength region are not as sharp and distinct as the undoped materials, and the absorption ranges are extended to even higher wavelength region.

Magnetism and Stability of Diluted Magnetic Semiconductor (Ga_(1-x)Fe_x)As

Magnetism and the stability of (Ga 1-xFe x)As are investigated using the first principles LMTO-ASA band calculation by assuming supercell structures.Four concentrations of the 3d impurities are studied (x=1,1/2,1/4,and 1/8).The results show the effect of varying Fe concentration on the magnetic and stable properties.

Room-temperature anomalous Hall effect and magnetroresistance in(Ga,Co)-codoped ZnO diluted magnetic semiconductor films

This paper reports that the （Ga, Co）-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition. Room-temperature ferromagnetism is observed for the as-grown thin films. The x-ray absorption fine structure characterization reveals that Co2＋ and Ga3＋ ions substitute for Zn2＋ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin. The ferromagnetic （Ga, Co）-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room tempera- ture. The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.

Energy Stabilities, Magnetic Properties, and Electronic Structures of Diluted Magnetic Semiconductor Zn1-xMnxS（001） Thin Films

We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn1-xMnxS（001） thin films with different Mn doping concentrations using the total energy density functional theory. The energy stability and density of states of a single Mn atom and two Mn atoms at various doped configurations and different magnetic coupling state were calculated. Different doping configurations have different degrees of p-d hybridization, and because Mn atoms are located in different crystal-field environment, the 3d projected densities of states peak splitting of different Mn doping configurations are quite different. In the two Mn atoms doped, the calculated ground states of three kinds of stable configurations are anti-ferromagnetic state. We analyzed the 3d density of states diagram of three kinds of energy stability configurations with the two Mn atoms in different magnetic coupling state. When the two Mn atoms are ferromagnetic coupling, due to d-d electron interactions, density of states of anti-bonding state have significant broadening peaks. As the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around S. For such these configurations, the antiferromagnetic coupling between Mn atoms is energetically more favorable.

Zn_(1-x)Co_xO Diluted Magnetic Semiconductor Bulk Prepared by Hot Pressing

Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h.The crystal structure and magnetic properties of Zn1-xCoxO bulks have been investigated by X-ray diffraction（XRD） and vibrating sample magnetometer（VSM）.X-ray photoelectron spectroscopy（XPS） was used to study chemical valence of zinc and cobalt in the samples.The results showed that Zn1-xCoxO samples had c-axis oriented wurtzite symmetry,neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15.Zn and Co existed in Zn0.9Co0.1O sample in Zn2＋ and Co2＋ states.The results of VSM experiment proved the room temperature ferromagnetic properties（RTFP） of Co-doped ZnO samples.The saturation magnetization and the coercivity of Zn0.9Co0.1O sample,observed in the M-H curve,were about 0.20 emu/g and 200 Oe,respectively.

Families of magnetic semiconductors——an overview

The interplay of magnetic and semiconducting properties has been in the focus for more than a half of the century. In this introductory article we briefly review the key properties and functionalities of various magnetic semiconductor families, including europium chalcogenides, chromium spinels, dilute magnetic semiconductors, dilute ferromagnetic semiconductors and insulators, mentioning also sources of non-uniformities in the magnetization distribution, accounting for an apparent high Curie temperature ferromagnetism in many systems. Our survey is carried out from today's perspective of ferromagnetic and antiferromagnetic spintronics as well as of the emerging fields of magnetic topological materials and atomically thin 2D layers.

Effects of Samarium Doping on Optical Properties of Zn_(0.9)(Co_(1-x)Sm_x )_(0.1)O Diluted Magnetic Semiconductor

Transparent ZnO and Zn0.9(Co1-xSmx)0.1O (x =0.0, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 1.0) films were prepared by sol-gel method. For the prepared Zn0.9(Co1-xSmx )0.1O systems, the influences of dopant concentration of Sm on the structural and optical properties were investigated. Three additional absorption peaks around 570, 620, and 660 nm wavelengths were observed in low Sm content films, which is attributed to the d-d transitions of Co2+ ions in tetrahedral crystalline. The redshift of band gap in doped samples was discussed in detail.

Preparation of Single Crystals of Co_xZn_(1-x)S and Co_xZn_(1-x)Se—New Materials of Dilute Magnetic Semiconductors

In this paper, we report the growth of single crystals of Co_x Zn_(1-x)S and Co_x Zn_(1-x)Se (0<x<0.3) by the method of chemical transport, using iodine as a transport agent. The light green color of single crystal Co_xZn_(1-x)S as well as the light brown color of Co_xZn_(1-x)Se become deep with an increase in x. The compositions of the single crystals were nearly stoichiometric. The transfer rate decreases with an increase of the x value. The growth rate was related to the temperature difference. The large temperature difference speed up the growth rate, but the size of crystal obtained was small. In general, the optimal temperature difference was 15℃. From X-ray diffraction measurements, the structures of crystals Co_xZn_(1-x)S and Co_xZn_(1-x)Se (0<x<0.1) were identified to be zinc blende structure similar to that of ZnS and ZnSe.

Mg and Ni Incorporated ZnO Diluted Magnetic Semiconductor for Magnetic and Photo-Catalytic Applications

Zinc oxide is recently being used as a magnetic semiconductor with the introduction of mag-netic elements.In this work,we report phase pure synthesis of Mg and Ni co-substituted ZnO to explore its structure,optical,magnetic and photo-catalytic properties.X-ray di raction analysis reveals the hexagonal wurtzite type structure having P63mc space group without any impurity phase.UV-Vis spectrophotometry demonstrates the variation in bandgap with the addition of Mg and Ni content in ZnO matrix.Magnetic measurements exhibit a clear boosted magnetization in Ni and Mg co-doped compositions with its stable value of bandgap corroborating the structural stability and magnetic tuning for its advanced applications in modern-day spintronic devices.Photo-catalytic measurements performed using methyl green degradation demonstrate an enhanced trend of activity in Mg and Ni co-doped compositions.

Room Temperature Ferromagnetism in Ga1-xHoxN （x=0.0 and 0.05） Diluted Magnetic Semiconductor Thin Films

Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea- surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor- phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper- ties of Gal-xHoxN （x=0.0, 0.05） films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films （i.e. GaN） exhibited diamagnetic behavior, while the Ho-doped （Gao.95Hoo.05N） film exhibited a ferro- magnetic behavior.

Magnetic Properties of Diluted Magnetic Semiconductor Hg_(0.89)Mn_(0.11)Te

The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer（SQUID Magnetometer）. First, magnetization measurements were done under various magnetic fi eld strengths from-20 kOe to 20 kOe at 5 K, 15 K, and 77 K, respectively. Then, the magnetizations were measured with continuous changes of temperature in the range from 5 K to 300 K under the magnetic field of 0.1 kOe and 10 kOe, respectively. The modifi ed Brillouin function was well fitted with the data of magnetization vs. magnetic field strength. The analysis indicated that there was an antiferromagnetic exchange coupling among Mn^2＋ ions. The results of reciprocal susceptibility vs. temperature fi t Curie-Weiss law very well at the temperatures above 40 K, but deviate from the law from 5 Kto 40 K, which shows that the antiferromagnetic exchange coupling among Mn^2＋ ions increases in the lower temperature range below 40 K. The experimental result was explained by extending higher-order terms in the calculation of susceptibility and fitted by a power law function. The measurements reveal that Hg0.89Mn0.11 Te possesses paramagnetic properties at temperatures from 5 K to 300 K.

Effect of defect complex on magnetic properties of (Fe, Mn)-doped ZnO thin films

We have observed room temperature ferromagnetism in Mn-doped and (Fe, Mn)-codoped ZnO thin films grown under different oxygen partial pressures by pulsed laser deposition. The X-ray diffraction and optical transmission spectra studies demonstrate the natural incorporation of Fe and Mn cations into wurtzite ZnO lattices. The effects of transition metal doping and defects on the magnetic properties was investigated. It is found that room temperature ferromagnetism is sensitive to oxygen vacancy and Zn vacancy. The absence of ferromagnetism in pure ZnO films grown under different oxygen partial pressures reveals that the transition metal ions should also play an important role in inducing the ferromagnetism.