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Register a new userIndependent magnetization behavior of a ferromagnetic metal/semiconductor hybrid system
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We report the discovery of an effect where two ferromagnetic materials, one semiconductor ((Ga,Mn)As) and one metal (permalloy), can be directly deposited on each other and still switch their magnetization independently. We use this independent magnetization behavior to create various resistance states dependent on the magnetization direction of the individual layers. At zero magnetic field a two layer device can reach up to four non-volatile resistance states.
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We fabricated a hybrid structure in which cobalt and permalloy micromagnets produce a local in-plane spin-dependent potential barrier for high-mobility electrons at the GaAs/AlGaAs interface. Spin effects are observed in ballistic transport in the tens millitesla range of the external field, and are attributed to switching between Zeeman and Stern-Gerlach modes -- the former dominating at low electron densities.
We have calculated the spin-polarization effects of a current in a two dimensional electron gas which is contacted by two ferromagnetic metals. In the purely diffusive regime, the current may indeed be spin-polarized. However, for a typical device geometry the degree of spin-polarization of the current is limited to less than 0.1%, only. The change in device resistance for parallel and antiparallel magnetization of the contacts is up to quadratically smaller, and will thus be difficult to detect.
Recent observations of a zero bias conductance peak in tunneling transport measurements in superconductor--semiconductor nanowire devices provide evidence for the predicted zero--energy Majorana modes, but not the conclusive proof for their existence. We establish that direct observation of a splitting of the zero bias conductance peak can serve as the smoking gun evidence for the existence of the Majorana mode. We show that the splitting has an oscillatory dependence on the Zeeman field (chemical potential) at fixed chemical potential (Zeeman field). By contrast, when the density is constant rather than the chemical potential -- the likely situation in the current experimental set-ups -- the splitting oscillations are generically suppressed. Our theory predicts the conditions under which the splitting oscillations can serve as the smoking gun for the experimental confirmation of the elusive Majorana mode.
We demonstrate the modification of coherent zone-folded longitudinal acoustic phonons (ZFLAPs) oscillations in InGaN/GaN multiple quantum wells by the inclusion of metal nanoparticles (Au and Ag) via self-assembled inverted hexagonal pits. Blueshift and redshift have been observed in photoluminescence spectra due to the effect of electrostatic charge of metal nanoparticles (NPs). A change in periodicity of ZFLAPs oscillations were demonstrated due to the metal NPs inserted in the material system.
Laser induced ultrafast demagnetization in ferromagnetic metals was discovered almost 20 years ago, but currently there is still lack of consensus on the microscopic mechanism responsible for the corresponding transfer of angular momentum and energy between electron, lattice and spin subsystems. A distinct, but intrinsically correlated phenomenon occurring on a longer timescale is the magnetization precession after the ultrafast demagnetization process, if a magnetic field is applied to tilt the magnetization vector away from its easy direction, which can be attributed to the change of anisotropy after laser heating. In an in-plane magnetized Pt/Co/Pt thin film with perpendicular interface anisotropy, we found excellent agreement between theoretical prediction with plausible parameters and experimental data measured using time resolved magneto-optical Kerr effect. This agreement confirms that the time evolution of the anisotropy field, which is driven by the interaction between electrons and phonons, determines the magnetization precession completely. A detailed analysis shows that, even though the whole sample is magnetized in-plane, the dynamic interface anisotropy field dictates the initial phase of the magnetization precession, highlighting the significance of the interface anisotropy field in laser induced magnetization precession.
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