Magnetic Properties Of Ga1 Research Articles

Theoretical study of the structure and magnetism of Ga1−xVxSb compounds for spintronic applications

In this paper, the structural, electronic, and magnetic properties of Ga1−xVxSb compounds with various vanadium (V) contents (x) ranging from dilute doping to the extreme doping limit were systematically investigated by first-principles calculations. The results show that V atoms prefer to substitute for gallium (Ga) atoms, and the formation energy is lower under Sb-rich growth conditions than under Ga-rich growth conditions. Meanwhile, the SbGa antisite defects effectively decrease the energy barrier of the substitution process from 0.85 to 0.53 eV. The diffusion of V atoms in the GaSb lattice occurs through metastable interstitial sites with an energy barrier of 0.6 eV. At a low V concentration (x = 0.0625), V atoms prefer a homogeneous distribution with antiferromagnetic coupling among the V atoms. However, when x increases above 0.5, the magnetic coupling among V atoms changes to ferromagnetic coupling due to the enhanced superexchange interaction between the eg and t2g states of neighboring V atoms. At the extreme doping limit of x = 1.00, zinc blende VSb along with its analogs VAs and VP is an intrinsic ferromagnetic semiconductor that exhibits a large change in light absorption at the Curie temperature. The results indicate that Ga1−xVxSb compounds provide a platform to design next-generation electronic, spintronic, and optoelectronic devices.

First-principles calculations on magnetism and exchange interactions in GaMnAs and GaMnAsP

Based on first principles calculations using a full potential linearized augmented plane wave (FP-LAPW) method in the local spin density approximation (LSDA) we calculated the electronic and magnetic properties of Ga1−xMnxAs and Ga1−xMnxAs1−yPy. The calculated electronic band structure and density of states of both diluted magnetic semiconductors (DMSs) are discussed. These results show a reduction in energy band gap in Ga1−xMnxAs doped with a small content of P atoms (6.25% atomic percent) compared to the undoped alloy Ga1−xMnxAs. Low exchange interaction constants, N0β, and JMn−Mn, and low exchange splitting, Δxpd, are observed in Ga1−xMnxAs1−yPy. The total magnetic moment calculated for Ga1−xMnxAs1−yPy is mainly attributed to the Mn atom, whereas the contributions from Ga, As, and P are minimal. The difference between the magnetic properties of Ga1−xMnxAs and Ga1−xMnxAs1−yPy is also discussed.

Investigations on the origin of ferromagnetism in Ga1−xCrxN and Si-doped Ga1−xCrxN films: Experiments and theory

In this paper, we combined experiments and first-principles calculations to investigate the physical properties especially the magnetic properties of Ga1−xCrxN and Si-doped Ga1−xCrxN thin films grown by molecular beam epitaxy. The results of experiments indicate that Si doping improved the crystallinity by improving the substitution of Ga in Si-doped Ga1−xCrxN. And the size and/or the number of vacancy defects are reduced in the Si-doped Ga1−xCrxN thin films. All the samples show room-temperature ferromagnetism, and the measured saturation magnetizations are 15 emu/cm3 (2.26 μB per Cr atom) and 10 emu/cm3 (1.31 μB per Cr atom) respectively for Ga1−xCrxN and Si-doped Ga1−xCrxN thin films. First-principles calculations based density-functional theory show that there is a strong magnetic coupling between the Ga vacancies and the impurities of Cr and Si ions. And Si doping reduced the saturation magnetization in Si-doped Ga1−xCrxN thin films which is in agreement with the experiment results. This intrinsic defect derived magnetic interaction plays an important role on improving the ferromagnetism in Ga1−xCrxN and Si-doped Ga1−xCrxN, and the ferromagnetism of the system is the result of long-range mediation between VGa, Cr and Si ions.

First-principles calculation on dilute magnetic alloys in zinc blend crystal structure

Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga1−xMnxX (X=P, As) compounds reveal that Ga0.75Mn0.25P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga0.75Mn0.25As and Ga0.5Mn0.5As and tune Ga0.25Mn0.75As to be metallic.Calculated total magnetic moments and the robustness of half-metallicity of Ga0.75Mn0.25P, Ga0.75Mn0.25As and Ga0.5Mn0.5As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices.

Effects of Si-doping on magnetic properties of Ga1−xCrxN

Abstract Ga1−xCrxN thin films with and without the Si doping have been prepared by molecular beam epitaxy. The samples have been investigated by X-ray diffraction, X-ray photoemission spectroscopy, photoluminescence, optical absorption spectra and magnetic measurements. It has been confirmed that for the undoped samples Cr in GaN is predominantly trivalent when substituting for Ga and that the Cr 3d state appears within the band gap of GaN. In Si doped specimens the upward shifts of the chemical potential are observed, and the electrons supplied by the Si doping are trapped at Cr sites forming Cr2+. As a result, the Si doping effects show an increase of the Curie temperature, and a reduction of the saturation magnetization in the Ga1−xCrxN:Si samples. The significant effect on the ferromagnetism with Si doping in Ga1−xCrxN is explained by the percolation theory of bound magnetic polarons.

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.

Annealing temperature effects on structural and magnetic properties of Ga1−xMnxN films

Amorphous gallium nitride doped with Mn thin films was deposited on sapphire (0001) substrates by laser molecular beam epitaxy. After simple processing of annealing at different temperatures for 30 min in ammonia atmosphere, good quality Ga1−xMnxN films were obtained. In order to investigate the influence of annealing temperature on the crystalline quality and structural and magnetic properties, the films are analysed by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and alternating gradient magnetic field meter. The results show that the annealing can improve the quality of Ga1−xMnxN films, and the optimum annealing temperature is 1050°C; moreover, there is no second phase forming. Through magnetic analysis, we obtained the annealed samples of room temperature ferromagnetic property and paramagnetism of the as grown film and obtained the way of changing the paramagnetism into ferromagnetism using the simple method.

Emergence of half metallicity in Cr-doped GaP dilute magnetic semiconductor compound within solubility limit

The electronic and magnetic properties of Ga1−xCrxP dilute magnetic semiconductor (DMS) compound for dopant concentration, x=0.25, 0.125, 0.06 and 0.03 have been investigated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method in order to seek out the possibility of new dilute magnetic semiconductor (DMS) compound within generalized gradient approximation (GGA) as exchange–correlation (XC) potential. The calculated results show that the Cr doping in GaP induces the ferromagnetism and originates a half metallic (HM) gap at Fermi level (EF) in minority spin channel (MIC) for all concentrations. The half metallicity is originated by the hybridization of Cr-d states with P-p states. Moreover, the half metallicity remains intact for all Cr-concentration. We also observed that the HM gap increases with the reduction in doping concentration from 0.25 to 0.03. The total magnetic moment of this compound is mainly due to Cr-d states present at EF. A small induced magnetic moment on other non magnetic atoms (Ga and P) for all doping concentrations is a consequence of p–d hybridization between Cr-d and P-p states.

Electrical and magnetic properties of Ga1−xGdxN grown by metal organic chemical vapor deposition

This paper presents the first report on Gd doping (0%–4%) of GaN thin films by metal organic chemical vapor deposition. The Ga1−xGdxN films grown in this study were found to be of good crystalline quality, single-phase, and unstrained, with a high saturation magnetization strength of 20 emu/cm3 being obtained for GaN films doped with 2% Gd at room temperature. Furthermore, these films were found to be conductive with an enhanced n-type behavior suggesting that unintentional donors are responsible for stabilizing the ferromagnetic phase in as-grown Ga1−xGdxN. Additionally, it was found that this magnetization can be enhanced by n-(Si: 1018 cm−3) and p-(Mg: 1019 cm−3) doping to 110 emu/cm3 and ∼500 emu/cm3, respectively. This paper shows empirically that holes are more efficient in stabilizing the ferromagnetic phase as compared to electrons. Overall, this research has resulted in a room temperature ferromagnetic dilute magnetic semiconductor that is conductive and whose magnetic properties can be tuned by carrier doping thus providing a path towards realizing spintronic devices.

Structural, optical and magnetic properties of Ga1−xMnxN films grown by MOCVD

In this paper, we have investigated the structural, optical and magnetic properties of Ga1−xMnxN films grown by MOCVD. The valence band structure was analysed by the x-ray photoelectron spectroscopy (XPS) measurements. A different Fermi level shift behaviour was observed with increasing Mn composition in the GaN. This shift behaviour was attributed to the donor-like defects induced by the Mn doping in the heavily doped samples. The presence of these defects was further confirmed by the calthodoluminescence spectra. The additional peak around 2.0 eV in the heavily doped samples corresponds to the intra-d-shell transitions of Mn2+. This Mn2+ state was formed by trapping the electrons released from the donor-like defects, which is quite consistent with the XPS results. Finally, the magnetic properties were also discussed in combination with the above results.

The Fermi level dependence of the optical and magnetic properties ofGa1−xMnxN grown by metal–organic chemical vapour deposition

The suppression of the ferromagnetic behaviour of metal–organic chemical vapour deposition grownGa1−xMnxN epilayers by silicon co-doping, and the influence of the Fermi levelposition on and its correlation with the magnetic and optical properties ofGa1−xMnxN are reported. Variation in the position of the Fermi level in the GaN bandgapis achieved by using different Mn concentrations and processing conditions aswell as by co-doping with silicon to control the background donor concentration.The effect on Mn incorporation on the formation of defect states and impurityinduced energy states within the bandgap of GaN was monitored by means ofphotoluminescence absorption and emission spectroscopy. A broad absorption detectedaround 1.5 eV is attributed to the presence of a subband introduced by Mn inducedenergy states due to temperature independent transition energies and linewidths.The intensity and the linewidth of the absorption band correlate with the Mnconcentration. Similarly, the magnitude of the magnetization decreases as the Fermilevel approaches the conduction band, as the Fermi energy is increased above theMn (0/−) acceptor state.Silicon concentrations>1019 cm−3 caused the complete loss of ferromagnetic behaviour in the epilayer. The absorption bandat 1.5 eV is also not observed upon silicon co-doping. The observed spectroscopic datafavour a double-exchange-like mechanism rather than an itinerant free carrier mechanismfor causing the ferromagnetism. This behaviour significantly differs from the propertiesreported for widely studied (Ga, In)MnAs.

Impact of Manganese incorporation on the structural and magnetic properties of MOCVD-grown Ga1−xMnxN

ABSTRACTThis paper reports the impact of the Mn incorporation on the structural and magnetic properties of Ga1−xMnxN on the metal-organic vapor phase deposition (MOCVD). Crystalline quality and phase purity were determined by high-resolution X-ray diffraction and indicated that no macroscopic second phases are formed during growth. Atomic force microscopy revealed a 2-dimensional MOCVD step-flow growth pattern in the Mn-incorporated samples. Various annealing steps were applied to some of the samples to reduce compensating defects and to investigate the effects of post processing on the growth. SQUID measurements showed an apparent ferromagnetic hysteresis behavior. However, none of the requirements for room temperature ferromagnetism in the prevailing mean field DMS theories were found. Therefore, different origins of the ferromagnetic signal are discussed.

Electronic structure and origin of ferromagnetism in Ga1−xMnxAs semiconductors

We perform a detailed theoretical study, within the density-functional theory, of the electronic structure and magnetic properties of Ga1−xMnxAs diluted semiconductors. Ab initio total energy results provide evidence that the appearance of a ferromagnetic state in these materials is due to an exchange coupling between the localized ↑ S=52 Mn spins mediated by quasi-localized ↓ holes, with strong p-like character, surrounding the fully polarized Mn d5-electrons. From total energy differences, we find the effective Mn–Mn coupling always ferromagnetic, with the Mn–Mn interaction intermediated by an antiferromagnetic coupling of each Mn spin to the holes.

Electronic and magnetic properties ofGa1−xMnxAs:Role of Mn defect bands

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Giant Negative Magnetoresistance of (Ga,Mn)As/GaAs in the Vicinity of a Metal-Insulator Transition

We have studied the transport and magnetic properties of Ga1—xMnxAs/GaAs with different Mn content (0.015 < x < 0.071). In these magnetic semiconductors, the exchange interaction between the carriers and the localized magnetic moments leads to unique transport properties. In this paper, we discuss an insulator–metal–insulator transition and a giant negative magnetoresistance observed in the vicinity of the metal–insulator transitions.