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Register a new userMicroscopic mechanism of high-temperature ferromagnetism in Fe, Mn, and Cr-doped InSb, InAs, and GaSb magnetic semiconductors
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In recent experiments, high Curie temperatures Tc above room temperature were reported in ferromagnetic semiconductors Fe-doped GaSb and InSb, while low Tc between 20 K to 90 K were observed in some other semiconductors with the same crystal structure, including Fe-doped InAs and Mn-doped GaSb, InSb, and InAs. Here we study systematically the origin of high temperature ferromagnetism in Fe, Mn, Cr-doped GaSb, InSb, and InAs magnetic semiconductors by combining the methods of density functional theory and quantum Monte Carlo. In the diluted impurity limit, the calculations show that the impurities Fe, Mn, and Cr have similar magnetic correlations in the same semiconductors. Our results suggest that high (low) Tc obtained in these experiments mainly comes from high (low) impurity concentrations. In addition, our calculations predict the ferromagnetic semiconductors of Cr-doped InSb, InAs, and GaSb that may have possibly high Tc. Our results show that the origin of high Tc in (Ga,Fe)Sb and (In,Fe)Sb is not due to the carrier induced mechanism because Fe3+ does not introduce carriers.
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Digital alloys of GaSb/Mn have been fabricated by molecular beam epitaxy. Transmission electron micrographs showed good crystal quality with individual Mn-containing layers well resolved; no evidence of 3D MnSb precipitates was seen in as-grown samples. All samples studied exhibited ferromagnetism with temperature dependent hysteresis loops in the magnetization accompanied by metallic p-type conductivity with a strong anomalous Hall effect (AHE) up to 400 K (limited by the experimental setup). The anomalous Hall effect shows hysteresis loops at low temperatures and above room temperature very similar to those seen in the magnetization. The strong AHE with hysteresis indicates that the holes interact with the Mn spins above room temperature. All samples are metallic, which is important for spintronics applications. * To whom correspondence should be addressed. E-mail: [email protected]
Electrotarnsport and magnetic properties of new phases in the system Cr-GaSb were studied. The samples were prepared by high-pressure (P=6-8 GPa) high-temperature treatment and identified by x-ray diffraction and scanning electron microscopy (SEM). One of the CrGa$_2$Sb$_2$ phases with an orthorhombic structure $Iba2$ has a combination of ferromagnetic and semiconductor properties and is potentially promising for spintronic applications. Another high-temperature phase is paramagnetic and identified as tetragonal $I4/mcm$.
We report on the micro-photoluminescence spectroscopy of InAs/GaAs quantum dots (QD) doped by a single Mn atom in a magnetic field either longitudinal or perpendicular to the optical axis. In both cases the spectral features of positive trion (X+) are found to split into strongly circularly polarized components, an effect very surprising in a perpendicular magnetic field. The field-induced splitting is ascribed to the transverse Zeeman splitting of the neutral acceptor complex A0 issued by the Mn impurity, whereas the circular optical selection rules result from the p-d exchange which acts as a very strong longitudinal magnetic field inhibiting the spin mixing by the transverse field of the QD heavy-hole ground state. A theoretical model of the spin interactions which includes (i) the local strain anisotropy experienced by the acceptor level and (ii) the anisotropic exchange due to the out-of-center Mn position provides a very good agreement with our observations.
High Curie temperature of 900 K has been reported in Cr-doped AlN diluted magnetic semiconductors prepared by various methods, which is exciting for spintronic applications. It is believed that N defects play important roles in achieving the high temperature ferromagnetism in good samples. Motivated by these experimental advances, we use a full-potential density-functional-theory method and supercell approach to investigate N defects and their effects on ferromagnetism of (Al,Cr)N with N vacancies (V_N). Calculated results are in agreement with experimental observations and facts of real Cr-doped AlN samples and their synthesis. Our first-principles results are useful to elucidating the mechanism for the ferromagnetism and exploring high-performance Cr-doped AlN diluted magnetic semiconductors.
In a recent letter, it has been predicted within first principle studies that Mn-doped ZrO2 compounds could be good candidate for spintronics application because expected to exhibit ferromagnetism far beyond room temperature. Our purpose is to address this issue experimentally for Mn-doped tetragonal zirconia. We have prepared polycrystalline samples of Y0.15(Zr0.85-yMny)O2 (y=0, 0.05, 0.10, 0.15 & 0.20) by using standard solid state method at equilibrium. The obtained samples were carefully characterized by using x-ray diffraction, scanning electron microscopy, elemental color mapping, X-ray photoemission spectroscopy and magnetization measurements. From the detailed structural analyses, we have observed that the 5% Mn doped compound crystallized into two symmetries (dominating tetragonal & monoclinic), whereas higher Mn doped compounds are found to be in the tetragonal symmetry only. The spectral splitting of the Mn 3s core-level x-ray photoelectron spectra confirms that Mn ions are in the Mn3+ oxidation state and indicate a local magnetic moment of about 4.5 {mu}B/Mn. Magnetic measurements showed that compounds up to 10% of Mn doping are paramagnetic with antiferromagnetic interactions. However, higher Mn doped compound exhibits local ferrimagnetic ordering. Thus, no ferromagnetism has been observed for all Mn-doped tetragonal ZrO2 samples.
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