Effect of low-temperature annealing on transport and magnetism of diluted magnetic semiconductor (Ga, Mn)As

Spin pumping is the phenomenon that magnetization precession in a ferromagnetic layer under ferromagnetic resonance produces a pure spin current in an adjacent non-magnetic layer. The pure spin current is converted to a charge current by the spin-orbit interaction, and produces a d.c. voltage in the non-magnetic layer, which is called the inverse spin Hall effect. The combination of spin pumping and inverse spin Hall effect has been utilized to determine the spin Hall angle of the non-magnetic layer in various ferromagnetic/non-magnetic systems. Magnetization dynamics of ferromagnetic resonance also produces d.c. voltage in the ferromagnetic layer through galvanomagnetic effects. Here we show a method to separate voltages of different origins using (Ga,Mn)As/p-GaAs as a model system, where sizable galvanomagnetic effects are present. Neglecting the galvanomagnetic effects can lead to an overestimate of the spin Hall angle by factor of 8, indicating that separating the d.c. voltages of different origins is critical.

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“…This heat treatment increases the Curie temperature T C of (Ga,Mn)As from 79 K to 118 K (ref. 31). The schematic of the sample is shown in Fig.…”

Section: Samplementioning

confidence: 99%

Direct-current voltages in (Ga,Mn)As structures induced by ferromagnetic resonance

2013

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“…xx as a function of temperature at H = 0 for Ga 0.941 Mn 0.059 As shows a peak due to the spin disorder scattering enhanced resistivity, 9 as shown in the inset of Fig. 1͑b͒.…”

mentioning

confidence: 92%

High-field magnetocrystalline anisotropic resistance effect in (Ga,Mn)As

Peng

Johnston-Halperin

et al. 2008

Phys. Rev. B

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As the magnetization rotates in the ͑001͒ plane of epitaxial ͑Ga,Mn͒As films, we observe both two-and fourfold oscillations of comparable magnitude in the longitudinal resistivity. This behavior is different from the usual anisotropic magnetoresistance effect in polycrystalline films. The fourfold or cubic symmetry vanishes at the Curie temperature T C , indicating that it originates from the long-range ferromagnetic phase in single crystal films. In contrast, the twofold symmetry persists above T C , suggesting its origin to be from the alignment of spins with random orientations. However, the transverse, or planar Hall, resistivity only contains a twofold oscillation. The temperature dependence of the magnetocrystalline anisotropic resistance effect is explained by a two-component model. The anisotropic magnetoresistance ͑AMR͒ effect in ferromagnetic ͑FM͒ materials arises from the difference in the scattering rate when the magnetization direction is oriented parallel or perpendicular to an electrical current. 1 It is a convenient tool often used for characterizing the state of the magnetization in ferromagnetic metals 2 and semiconductors. 3,4 In ferromagnetic semiconductors such as GaMnAs, AMR has been linked to the intrinsic band structure properties in the presence of spin-orbit interaction. 5 For polycrystalline materials, the resistivity typically shows a twofold symmetry because the magnetocrystalline effect in the randomly oriented grains is averaged out. In single crystal films, however, also due to the spin-orbit interaction, AMR may contain higher-order terms that reflect the symmetry of the crystals. 6 Nevertheless, in many cases, the highorder terms are small and often neglected. 7,8 Here, we have conducted a series of experiments in epitaxially grown GaMnAs films and found a very strong fourfold magnetoresistance effect that is correlated with the crystalline symmetry of the films. This fourfold term is found to be connected to the long-range FM order below T C ; therefore, its temperature and field dependences reveal valuable information about the ferromagnetic ordering in the materials.We studied two Ga 1−x Mn x As samples with x = 0.039 and 0.059 which were grown on GaAs͑001͒ wafers at 250°C by molecular beam epitaxy in an As-rich environment. The samples were patterned into the standard Hall bar using photolithography and wet chemical etching. For resistivity measurements, the current flows along a ͓110͔ direction, as schematically shown in Fig. 1͑a͒, and both the longitudinal and transverse or the planar Hall dc resistivities xx and xy are measured simultaneously using the four-probe method. The measurements are performed in a superconducting magnet equipped with a rotating sample holder, which allows us to continuously change the angle between the magnetic field H and the electric current I, as illustrated in Fig. 1͑a͒. As the sample is rotated around ͓001͔, H always lies in the sample plane, and both xx and xy are recorded as angle is varied. The angular dependence is taken for different...

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“…1 The impending need to obtain such devices has led to the growing interest in developing and designing new spintronic materials. Starting from the initial works of Ohno et al on Mn-doped GaAs, which is a ferromagnetic semiconductor with T c ϳ 110 K, 2 there have been continuous efforts to obtain such systems with high T c , preferably close to room temperature, [3][4][5] and also to provide a thorough understanding of the origin of ferromagnetism [6][7][8] in systems like Mn-and Cr-doped GaAs, InAs, GaN, and AlN. Earlier studies 9 on some ͑II-VI͒-based doped semiconducting systems like Mn-doped ZnTe and CdTe were not successful and resulted in T c values only of the order of a few kelvin.…”

Section: Introductionmentioning

confidence: 99%

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

et al. 2007

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Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature above 450 K with a low-temperature transition from the ferromagnetic to the spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like electron paramagnetic resonance and Mössbauer spectroscopy indicate the presence of Fe in both valence states Fe 2+ and Fe 3+ . We argue that the presence of Fe 3+ is due to possible hole doping in the system by cation ͑Zn͒ vacancies. In a subsequent ab initio electronic structure calculation, the effects of defects ͑e.g., O and Zn vacancies͒ on the nature and origin of ferromagnetism are investigated for the Fe-doped ZnO system. Electronic structure calculations suggest hole doping ͑Zn vacancy͒ to be more effective to stabilize ferromagnetism in Fe-doped ZnO and our results are consistent with the experimental signature of hole doping in ferromagnetic Fe-doped ZnO samples.

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Effect of low-temperature annealing on transport and magnetism of diluted magnetic semiconductor (Ga, Mn)As

Cited by 267 publications

References 14 publications

Direct-current voltages in (Ga,Mn)As structures induced by ferromagnetic resonance

Direct-current voltages in (Ga,Mn)As structures induced by ferromagnetic resonance

High-field magnetocrystalline anisotropic resistance effect in (Ga,Mn)As

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

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