Dilute Ferromagnetic Semiconductors Research Articles

Plotting philosophy picture of uniaxial magnetic anisotropy in arsenide and phosphide dilute ferromagnetic semiconductors

In this work, we performed a systematic investigation on the comparison of magnetic anisotropy between three III-Mn-V dilute ferromagnetic semiconductors (Ga,Mn)As, (In,Mn)As and (Ga,Mn)P prepared by ion implantation and pulsed laser melting. Compressive strain induces in-plane magnetic anisotropy in (Ga,Mn)As and (Ga,Mn)P, while out-of-plane magnetic anisotropy is present in (In,Mn)As due to tensile strain introduced by Mn substitution. Interestingly, all materials prepared herein does not present strong in-plane uniaxial anisotropy, between [110] and [11¯0] directions, which always exhibits in low temperature molecular beam epitaxy (LT-MBE) grown (Ga,Mn)As samples. The reason is ascribed to the fact that the ultra-fast recrystallization induced by pulsed laser melting weakens the formation of Mn-Mn dimers along the [11¯0] direction which presents in LT-MBE grown (Ga,Mn)As.

Recent advances in application-oriented new generation diluted magnetic semiconductors

Diluted ferromagnetic semiconductors (DMSs) have attracted widespread attention in last decades, owing to their potential applications in spintronic devices. But classical group-III-IV, and -V elements based DMS materials, such as (Ga,Mn)As which depend on heterovalent (Ga<sup>3+</sup>, Mn<sup>2+</sup>) doping, cannot separately control carrier and spin doping, and have seriously limited chemical solubilities, which are disadvantages for further improving the Curie temperatures. To overcome these difficulties, a new-generation DMS with independent spin and charge doping have been designed and synthesized. Their representatives are I-II-V based Li(Zn,Mn)As and II-II-V based (Ba,K)(Zn,Mn)<sub>2</sub>As<sub>2</sub>. In these new materials, doping isovalent Zn<sup>2+</sup> and Mn<sup>2+</sup> introduces only spins, while doping heterovalent non-magnetic elements introduces only charge. As a result, (Ba,K)(Zn,Mn)<sub>2</sub>As<sub>2</sub> achieves Curie temperature of 230 K, a new record among DMS where ferromagnetic orderings are mediated by itinerate carriers. Herein, we summarize the recent advances in the new-generation DMS materials. The discovery and synthesis of several typical new-generation DMS materials are introduced. Physical properties are studied by using muon spin relaxation, angle-resolved photoemission spectroscopy and pair distribution function. The physical and chemical pressure effects on the title materials are demonstrated. The Andreev reflection junction based on single crystal and the measurement of spin polarization are exhibited. In the end, we demonstrate the potential multiple-parameter heterojunctions with DMSs superconductors and antiferromagnetic materials.

Ferromagnetic Order in Semiconducting Cr‐Doped α‐MnTe Nanosheets Grown by Chemical Vapor Deposition

AbstractFerromagnetic semiconductors (FMSs) have been extensively investigated to fulfill the prospect of simultaneous control spin and charge of electron over the past decades. However, it is still highly desirable to identify new ferromagnetic semiconductors with robust and reliable sign of coexistence of semi‐conductivity and ferromagnetism, especially for those ultrathin film systems with great potential for electrical gating. Here, ultrathin Cr‐doped α‐MnTe nanosheets can be readily prepared via a facile chemical vapor deposition (CVD) method, which sustain the crystal structure of parent α‐MnTe but exhibit utterly changed electrical and magnetic properties. Derived from anomalous Hall measurements, the CVD‐grown sample presented a robust out‐of‐plane ferromagnetic order with Curie temperature of ≈210 K and a large coercivity >3.5 T at 2 K. Additionally, Cr‐doped α‐MnTe nanosheets show tunable ferromagnetism and different gating effects with varied thicknesses. The theoretical calculation is performed to explain the origin of its ferromagnetism and semi‐conductivity, probably attributed to the specific antiferromagnetic arrangement of each Mn/Cr plane and non‐zero net magnetic moment with Cr introducing. The work sheds new light on the development of dilute ferromagnetic semiconductors and spintronics.

Modulating properties by light ion irradiation: From novel functional materials to semiconductor power devices

In this review, the application of light ion irradiation is discussed for tailoring novel functional materials and for improving the performance in SiC or Si based electrical power devices. The deep traps and electronic disorder produced by light ion irradiation can modify the electrical, magnetic, and optical properties of films (e.g., dilute ferromagnetic semiconductors and topological materials). Additionally, benefiting from the high reproducibility, precise manipulation of functional depth and density of defects, as well as the flexible patternability, the helium or proton ion irradiation has been successfully employed in improving the dynamic performance of SiC and Si based PiN diode power devices by reducing their majority carrier lifetime, although the static performance is sacrificed due to deep level traps. Such a trade-off has been regarded as the key point to compromise the static and dynamic performances of power devices. As a result, herein the light ion irradiation is highlighted in both exploring new physics and optimizing the performance in functional materials and electrical devices.

Physical properties of Mn- and Fe-doped CaS: A DFT insights

In the present paper, we investigate the structural, electronic magnetic and elastic properties of ordered dilute ferromagnetic semiconductors Ca0.75Mn0.25S and Ca0.75Fe0.25S using the full-potential linearized augmented plane-wave (FP-LAPW) method. We adopt the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), GGA-PBE + U and the modified Becke-Johnson exchange potential for the exchange-correlation energy and potential. The spin-polarized electronic band structures and density of states of Ca0.75Fe0.25S calculated by GGA-PBE, mBJ-GGA-PBE and GGA-PBE + U show that the minority spin channel has metallic nature and the majority spin channel has a half-metallic gap of 0.74,0.78 and 0.54 eV, respectively. For Ca0.75Mn0.25S the band structures calculated within GGA-PBE and mBJ-GGA-PBE shows a half-metallic behavior, whereas when we use the GGA-PBE + U, we see that this compound is semiconductor with magnetic moment of 5 μB per formula unit. Moreover, the elastic constants, bulk modulus, shear modulus, and universal elastic anisotropy are calculated, which have not been measured yet. Analysis of elastic constants demonstrated that both Ca0.75Mn0.25S and Ca0.75Fe0.25S are mechanically stable.

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.

Hole compensation effect in III-Mn-V dilute ferromagnetic semiconductors

A systematic study of hole compensation effect on magnetic properties, which is controlled by defect compensation through ion irradiation, in (Ga,Mn)As, (In,Mn)As and (Ga,Mn)P is represented in this work. In all materials, both Curie temperature and magnetization decrease upon increasing the hole compensation, confirming the description of hole mediated ferromagnetism according to the p -d Zener model. The material dependence of Curie temperature and magnetization versus hole compensation reveals that the manipulation of magnetic properties in III-Mn-V dilute ferromagnetic semiconductors by ion irradiation is strongly influenced by the energy level location of the produced defect relative to the band edges in semiconductors.

Ba(Zn,Co)2As2 : A diluted ferromagnetic semiconductor with n -type carriers and isostructural to 122 iron-based superconductors

Diluted ferromagnetic semiconductors (DMSs) that combine the properties of semiconductors with ferromagnetism have potential application in spin-sensitive electronics (spintronics) 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 $T_C$ of 230 K has been achieved in (Ba,K)(Zn,Mn)$_2$As$_2$. However, most DMSs, including (Ga,Mn)As, are p-type, i.e., the carriers that mediate ferromagnetism are holes. For practical applications, DMS with n-type carriers are also advantageous. Here we report the successful synthesis of a II-II-V diluted ferromagnetic semiconductor with n-type carriers, Ba(Zn,Co)$_2$As$_2$. Magnetization measurements show that the ferromagnetic transition occurs up to $T_{C} \sim$ 45 K. Hall effect and Seebeck effect measurements jointly confirm that the dominant carriers are electrons. Through muon spin relaxation ($\mu$SR), a volume sensitive magnetic probe, we have also confirmed that the ferromagnetism in Ba(Zn,Co)$_2$As$_2$ is intrinsic and the internal field is static.

Recent progress of a new type diluted magnetic semiconductors with independent charge and spin doping

Due to the potential applications for spintronics devices, diluted ferromagnetic semiconductors (DMS) have received extensive attention for decades. However, in classical Ⅲ–Ⅴ based DMS material, such as (Ga,Mn)As, heterovalent (Ga<sup>3+</sup>, Mn<sup>2+</sup>) doping results in lack of individual control of carrier and spin doping, and seriously limited chemical solubility. The two difficulties prevent furtherincrease of the Curie temperature of the Ⅲ–Ⅴ based DMS. To overcome these difficulties, a series of new types of DMS with independent spin and charge doping have been synthesized, such as Ⅰ–Ⅱ–Ⅴ based LiZnAs and Ⅱ–Ⅱ–Ⅴ based (Ba,K)(Zn,Mn)<sub>2</sub>As<sub>2</sub>. In these new materials, isovalent (Zn,Mn) substitution is only spin doping, while charge is independently doped by heterovalentsubstitution of non-magnetic elements. As a result (Ba,K)(Zn,Mn)<sub>2</sub>As<sub>2</sub> obtains the reliable record of Curie temperature (230 K) among DMS in which ferromagnetic ordering is mediated by itinerate carriers. In this review, we summarize the recent development of the new DMS materials with following aspects: 1) the discovery and synthesis of several typical new DMS materials; 2) physical properties studies with muon spin relaxation and in-situ high pressure techniques; 3) single crystal growth, Andreev reflection junction based on single crystal and measurements of spin polarization.

Cubic anisotropy in (Ga,Mn)As layers: Experiment and theory

Historically, comprehensive studies of dilute ferromagnetic semiconductors, e.g., $p$-type (Cd,Mn)Te and (Ga,Mn)As, paved the way for a quantitative theoretical description of effects associated with spin-orbit interactions in solids, such as crystalline magnetic anisotropy. In particular, the theory was successful in explaining {\em uniaxial} magnetic anisotropies associated with biaxial strain and non-random formation of magnetic dimers in epitaxial (Ga,Mn)As layers. However, the situation appears much less settled in the case of the {\em cubic} term: the theory predicts switchings of the easy axis between in-plane $\langle 100\rangle$ and $\langle 110\rangle$ directions as a function of the hole concentration, whereas only the $\langle 100\rangle$ orientation has been found experimentally. Here, we report on the observation of such switchings by magnetization and ferromagnetic resonance studies on a series of high-crystalline quality (Ga,Mn)As films. We describe our findings by the mean-field $p$-$d$ Zener model augmented with three new ingredients. The first one is a scattering broadening of the hole density of states, which reduces significantly the amplitude of the alternating carrier-induced contribution. This opens the way for the two other ingredients, namely the so-far disregarded single-ion magnetic anisotropy and disorder-driven non-uniformities of the carrier density, both favoring the $\langle 100\rangle$ direction of the apparent easy axis. However, according to our results, when the disorder gets reduced a switching to the $\langle 110\rangle$ orientation is possible in a certain temperature and hole concentration range.

P-type co-doping effect of (Ga,Mn)P: Magnetic and magneto-transport properties

In this paper, we perform a comparison of magnetic and electrical properties between Mn-doped and (Mn, Zn) co-doped GaP dilute ferromagnetic semiconductors. Due to the shallow Zn impurity level (∼20–40 meV above the top of the III-V compounds valence band), the Zn co-doping leads to the increase of conductivity of (Ga,Mn)P, however both the Curie temperature and magnetization reduce, which is probably due to the suppression of active Mn substitution by Zn co-doping.

Interplay between localization and magnetism in (Ga,Mn)As and (In,Mn)As

Ion implantation of Mn combined with pulsed laser melting is employed to obtain two representative compounds of dilute ferromagnetic semiconductors (DFSs): Ga1-xMnxAs and In1-xMnxAs. In contrast to films deposited by the widely used molecular beam epitaxy, neither Mn interstitials nor As antisites are present in samples prepared by the method employed here. Under these conditions the influence of localization on the hole-mediated ferromagnetism is examined in two DFSs with a differing strength of p-d coupling. On the insulating side of the transition, ferromagnetic signatures persist to higher temperatures in In1-xMnxAs compared to Ga1-xMnxAs with the same Mn concentration x. This substantiates theoretical suggestions that stronger p-d coupling results in an enhanced contribution to localization, which reduces hole-mediated ferromagnetism. Furthermore, the findings support strongly the heterogeneous model of electronic states at the localization boundary and point to the crucial role of weakly localized holes in mediating efficient spin-spin interactions even on the insulator side of the metal-insulator transition.

ChemInform Abstract: Dilute Ferromagnetic Semiconductors Prepared by the Combination of Ion Implantation with Pulse Laser Melting

AbstractReview: 183 refs.

Model for the Surface Anisotropy Field Observed in Spin-Wave Resonance in (Ga,Mn)As Thin Films

Dilute ferromagnetic semiconductors are a class of very promising materials of the future [1 6]. Gallium manganese arsenide (Ga,Mn)As, created on the basis of the semiconductor gallium arsenide by the addition of a small percentage of manganese as a magnetic dopant, is one of the most intensively studied compounds in this class [7 12]. Spin-wave resonance in thin lms has been studied particularly intensively in gallium manganese arsenide in the past decade [13 21]. Especially rich resonance spectra were obtained in studies with a variable con guration of the static eld with respect to the lm surface. The eld was rotated perpendicularly to the lm surface, which corresponds to variable polar angle θH between the direction of the external eld and the surface normal. In the present paper we shall analyze SWR measurement data concerning the out-of-plane rotation of the magnetic eld, mainly because of the controversy that arose in the interpretation of these results over an issue which therefore requires elucidation. If researchers tend to agree on the interpretation of SWR spectra in two extreme con gurations the perpendicular and parallel con gurations, corresponding to θH = 0 and θH = 90 ◦, respectively the interpretation of results obtained in intermediate con gurations is under debate. Almost as a rule, a particular con guration of the external eld tends to occur in this range at a critical angle θ H , for which the multi-peak SWR spectrum collapses to a single-peak FMR spectrum. There are two schools of thought regarding the interpretation of the occurrence of this critical angle. Both schools agree that in the critical con guration the thin lm is magnetically homogeneous, and the boundary conditions (speci cally, the surface spin pinning) correspond to the natural conditions, only resulting from the reduced neighborhood of the surface

Ohmic contacts of Au and Ag metals to n-type GdN thin films

The rare-earth nitrides appear as attractive alternatives to dilute ferromagnetic semiconductors for spintronics device applications. Most of them combine the properties of the ferromagnet and the semiconductor, an exceedingly rare combination. In this work we have grown n-type polycrystalline semiconducting GdN layers between pre-deposited contacts made of Cr/Au and Cr/Ag. The resistivity of the GdN layers ranges from 4.4×10-4 Ωcm to 3.1×10-2 Ωcm depending on the nitrogen pressure during the growth. The electrical properties of metal/n-type GdN/metal planar junctions are investigated as a function of the temperature. The current voltage characteristics of the junctions were linear for temperatures ranging from 300 K down to 5 K, suggesting an ohmic contact between the Au or Ag metal and the n-type GdN layer.

Enhancing magnetic ordering in Cr-doped Bi2Se3 using high-TC ferrimagnetic insulator.

We report a study of enhancing the magnetic ordering in a model magnetically doped topological insulator (TI), Bi(2-x)Cr(x)Se(3), via the proximity effect using a high-TC ferrimagnetic insulator Y(3)Fe(5)O(12). The FMI provides the TI with a source of exchange interaction yet without removing the nontrivial surface state. By performing the elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally observed an enhanced TC of 50 K in this magnetically doped TI/FMI heterostructure. We have also found a larger (6.6 nm at 30 K) but faster decreasing (by 80% from 30 to 50 K) penetration depth compared to that of diluted ferromagnetic semiconductors (DMSs), which could indicate a novel mechanism for the interaction between FMIs and the nontrivial TIs surface.

“1111” 型稀磁半导体的研究进展

We successfully fabricated “1111” type bulk form diluted ferromagnetic semiconductors (DMS) with decoupled carriers and spins doping:(La,AE)(Zn,TM)AsO (AE Ba, Sr; TM = Mn, Fe), of which the Curie temperature TC up to 40 K. We investigated the individual influence of carriers and local moments on the ferromagnetic ordering in (La1- x Sr x )(Zn0.9Mn0.1)AsO by fixing Mn at the level of 0.10, and vary the doping levels of Sr. When the Sr doping level is 10%, a ferromagnetic ordering below ~ 30 K is observed. But both TC and saturation moments are heavily suppressed when the Sr doping level is increased to x = 0.30. We investigated the spin dynamics by microscopic techniques of mSR and Neutron Scattering. The results of mSR measurements indicate that the ferromagnetic order transition takes place in entire volume, namely, these DMSs are bulk nature. The μSR measurements also show an universal linear trend between the static internal field parameter as and the ferromagnetic Curie temperature TC for 1111-type system, (Ga,Mn)As, the 111- type system Li(Zn,Mn)As and the 122-type system (Ba,K)(Zn,Mn)2As2, which suggests that the exchange interaction supporting ferromagnetic coupling in these systems has a common origin. The researches on this series of DMS will be helpful to reveal the general mechanism of ferromagnetism shared in diluted ferromagnetic semiconductors including (Ga, Mn)As.

DFT modeling of Mn charged states in Ga1 − x Mn x As diluted ferromagnetic semiconductors: The cluster approach

Quantum chemical cluster modeling of the high-symmetry nanoclusters Ga15MnAs16H36 and Ga12MnAs16H36 simulating the bulk of a GaAs crystal with Mn paramagnetic impurity center is carried out within the Density Functional Theory. A Generalized Gradient Approximation method PBEPBE/LanL2DZ is used to study the neutral Mn0 and ionized Mn− states of a Mn atom in the nanoclusters under consideration. The change of the charge state of the impurity center from Mn0 to Mn− leads to a considerable relaxation of Mn-As bonds in the immediate surroundings of the Mn atom and to the “p-hole” recombination. It also affects the spin density localization. The components of the g-tensor for both the neutral Mn0 and the ionized Mnstates are calculated by the Gauge-Independent Atomic Orbital (GIAO) method with the hybrid density-functional mPW1PW91. The resulting values of the g-factor are in good agreement with the experimental Electron Paramagnetic Resonance data. The results obtained confirm the applicability of the cluster approach for describing charge effects in dilute ferromagnetic semiconductors.

Dilute ferromagnetic semiconductors: Physics and spintronic structures

This review compiles results of experimental and theoretical studies on thin films and quantum structures of semiconductors with randomly distributed Mn ions, which exhibit spintronic functionalities associated with collective ferromagnetic spin ordering. Properties of $p$-type Mn-containing III-V as well as II-VI, IV-VI, ${V}_{2}\text{\ensuremath{-}}{\mathrm{VI}}_{3}$, I-II-V, and elemental group IV semiconductors are described, paying particular attention to the most thoroughly investigated system (Ga,Mn)As that supports the hole-mediated ferromagnetic order up to 190 K for the net concentration of Mn spins below 10%. Multilayer structures showing efficient spin injection and spin-related magnetotransport properties as well as enabling magnetization manipulation by strain, light, electric fields, and spin currents are presented together with their impact on metal spintronics. The challenging interplay between magnetic and electronic properties in topologically trivial and nontrivial systems is described, emphasizing the entangled roles of disorder and correlation at the carrier localization boundary. Finally, the case of dilute magnetic insulators is considered, such as (Ga,Mn)N, where low-temperature spin ordering is driven by short-ranged superexchange that is ferromagnetic for certain charge states of magnetic impurities.

First-principles investigations of structural, elastic, electronic and magnetic properties of Ga1−x Mn x P and In1−x Mn x P

We employ the full-potential linearized augmented plane wave plus local orbital (FP L/APW + lo) method based on the density functional theory (DFT) in order to investigate the structural, elastic, electronic, and magnetic properties of ordered dilute ferromagnetic semiconductors Ga1−x Mn x P and In1−x Mn x P at (x = 0.25) in the zinc blende phase, using generalized gradient approximation, GGA (PBE). To our knowledge the elastic constants of these compounds have not yet been measured or calculated, hence our results serve as a first quantitative theoretical prediction for future study. Results of calculated electronic structures and magnetic properties reveal that both Ga0.75Mn0.25P and In0.75Mn0.25P have stable ferromagnetic ground state, and they are ideal half-metallic (HM) ferromagnetic at their equilibrium lattice constants. Also we show the nature of the bonding from the charge spin-densities calculations. The calculated total magnetic moments are 4.0 μB per unit cell for both Ga0.75Mn0.25P and In0.75Mn0.25P, which agree with the Slater–Pauling rule quite well, and we observe that p–d hybridization reduces the local magnetic moment of Mn from its free space charge value and produces smaller local magnetic moments on the nonmagnetic Ga, In and P sites. The values of N 0α and N 0β exchange constants confirm the magnetic nature of these compounds. From the robust half-metallicity of Ga0.75Mn0.25P and In0.75Mn0.25P as a function of lattice constant is also investigated.