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.

Progress of novel diluted ferromagnetic semiconductors with decoupled spin and charge doping: Counterparts of Fe-based superconductors

Diluted ferromagnetic semiconductors（DMSs） that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronic（spintronic） devices. The search for DMS materials exploded after the observation of ferromagnetic ordering in Ⅲ-Ⅴ（Ga,Mn）As films. Recently, a series of DMS compounds isostructural to iron-based superconductors have been reported. Among them, the highest Curie temperature TCo f 230 K has been achieved in（Ba,K）（Zn,Mn）2As2. However, most DMSs, including（Ga,Mn）As, are p-type, i.e., the carriers that mediate the ferromagnetism are holes. For practical applications, DMSs with n-type carriers are also advantageous. Very recently,a new DMS Ba（Zn,Co）2As2 with n-type carriers has been synthesized. Here we summarize the recent progress on this research stream. We will show that the homogeneous ferromagnetism in these bulk form DMSs has been confirmed by microscopic techniques, i.e., nuclear magnetic resonance（NMR） and muon spin rotation（μSR）.

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.

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.

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.

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.

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.

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.

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.

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.

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.

(Ca,K)(Zn,Mn)_(2)As_(2):Ferromagnetic semiconductor induced by decoupled charge and spin doping in CaZn_(2)As_(2)

We have successfully synthesized a novel diluted magnetic semiconductor(Ca_(1−2x)K_(2x))(Zn_(1−x)Mn_(x))_(2)As_(2) with decoupled charge and spin doping.The substitutions of(Ca^(2+),K^(+))and(Zn^(2+),Mn^(2+))in the parent compound CaZn_(2)As_(2)(space group P m1(No.164))introduce carriers and magnetic moments,respectively.Doping only Mn into CaZn_(2)As_(2) does not induce any type of long range magnetic ordering.The ferromagnetic ordering arise can only when K^(+)and Mn^(2+)are simultaneously doped.The res-ulted maximum Curie temperature reaches~7 K,and the corresponding coercive field is~60 Oe.The transport measurements confirm that samples with K and Mn co-doping still behave like a semiconductor.

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.

Phase diagram of Er-Sn-Te system for diluted magnetic semiconductor developments

Phase diagrams of the RE （rare earth）-Ⅳ-Ⅵ systems are very important for the design of rare earth doped diluted magnetic semiconductors （DMSs）, but related information is very limited. In this work, the phase equilibria of the Er-Sn-Te system in whole compositional range at room temperature were investigated mainly by means of X-ray powder diffraction （XRD） and differential thermal analysis （DTA）. The existences of 9 binary compounds, i.e., SnTe, ErTe3, EraTe3, ErTe, ErsSn3, Er11Sn10, ErSn2, Er3Sn7 and Er2Sn5 were confirmed. The phase diagram consisted of 12 single-phase regions, 21 binary phase regions and 10 ternary phase re- gions. The maximum solid solubility of Er in SnTe was determined to be about 7.5 at.%, none of the other phases in this system re- vealed a remarkable homogeneity range at room temperature. No ternary compound was found in this work.

Microstructure and ferromagnetism of heavily Mn doped SiGe thin flims

Heavily Mn-doped SiGe thin films were grown by radio frequency magnetron sputtering and then treated by postgrowth thermal annealing.Structural characterizations reveal the coexistence of Mn-diluted SiGe crystals and Mn-rich nanoclusters in the annealed films.Magnetic measurements indicate the ferromagnetic ordering of the annealed samples above room temperature.The data suggest that the ferromagnetism is probably mainly contributed by the Ge-rich nanoclusters and partially contributed by the tensile-strained Mn-diluted SiGe crystals.The results may be useful for room temperature spintronic applications based on group IV semiconductors.

Room temperature ferromagnetism of Si-doped ZnO thin films prepared by sol-gel method

Pure ZnO and Si-doped ZnO thin films were deposited on quartz substrate by using sol-gel spin coating process. X-ray diffraction analysis shows that all the thin films have hexagonal wurtzite structure and preferred c-axis orientation. Si-doped ZnO films show room temperature ferromagnetism （RTFM） and reach the maximum saturation magnetization value of 1.54 kA.m at 3 % Si concentration. RTFM of Si-doped ZnO decreases with the increasing annealing temperature because of the formation of SiO2. Photoluminescence measurements suggest that the RTFM in Si-doped ZnO can be attributed to the defect complex related to zinc vacancies Vzn and oxygen interstitials O1.

The effects of Zn vacancies on ferromagnetism in Cu-doped ZnO films controlled by oxygen pressure and Li doping

Zn0.99Cu0.01O films were studied experimentally and theoretically. The films were prepared by pulsed-laser deposition on Pt（111）/Ti/SiO2/Si substrates under various oxygen pressures to investigate the growth-dependence of the ferromagnetic properties. The structural, magnetic, and optical properties were studied, and it was found that all the samples possess a typical wurtzite structure, and that the films exhibit room-temperature ferromagnetism. The sample deposited at 600 ℃ and an oxygen pressure of 10 Pa showed a large saturation magnetization of 0.83 μB/Cu. The enhanced ferromagnetism in the （Cu, Li）-codoped ZnO is attributable to the existence of Zn vacancies （Vzn）, as shown by first-principles calcu- lations. The photoluminescence analysis demonstrated the existence of Vzn in both Zn0.99Cu0.01 O and （Cu, Li）-codoped ZnO thin films, and this plays an important role in the increase of ferromagnetism, according to the results of first-principles calculations.

Fabrication and Characterization of Well-Aligned Zn1-xMnxO Nanorods

Well-Migned Zn1-xMnxO nanorods have been synthesized successfully on bare silicon substrates by a simple evaporation method without using any catalyst. X-ray diffraction and electron microscopy studies demonstrate that the as-grown nanorods are of single wurtzite phase with a preferential growth direction along their c- axes, Quantitative energy-dispersive spectrum analysis reveals that the concentration of manganese is around 4 at,%, Magnetic measurements show the single-phase Zn1-xMnxO nanorod arrays exhibiting the paramagnetic behaviour. Photolumlnescence spectra demonstrate that the Zn1-xMnxO nanorods preserve ultraviolet emission at room temperature.