Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal ...structure and relativistic spinorbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spinorbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga,Mn)As, in which spinorbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spinorbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spinorbit torques generated by eective elds of the expected symmetry and of a magnitude consistent with our ab initio calculations.
Recent experiments on strongly coupled microwave and ferromagnetic resonance modes have focused on large volume bulk crystals such as yttrium iron garnet, typically of millimeter-scale dimensions. We ...extend these experiments to lower volumes of magnetic material by exploiting low-impedance lumped-element microwave resonators. The low impedance equates to a smaller magnetic mode volume, which allows us to couple to a smaller number of spins in the ferromagnet. Compared to previous experiments, we reduce the number of participating spins by two orders of magnitude, while maintaining the strength of the coupling rate. Strongly coupled devices with small volumes of magnetic material may allow the use of spin orbit torques, which require high current densities incompatible with existing structures.
Spin-dependent transport phenomena due to relativistic spin-orbit coupling and broken space-inversion symmetry are often difficult to interpret microscopically, in particular when occurring at ...surfaces or interfaces. Here we present a theoretical and experimental study of spin-orbit torque and unidirectional magnetoresistance in a model room-temperature ferromagnet NiMnSb with inversion asymmetry in the bulk of this half-Heusler crystal. Aside from the angular dependence on magnetization, the competition of Rashba- and Dresselhaus-type spin-orbit couplings results in the dependence of these effects on the crystal direction of the applied electric field. The phenomenology that we observe highlights potential inapplicability of commonly considered approaches for interpreting experiments. We point out that, in general, there is no direct link between the current-induced nonequilibrium spin polarization inferred from the measured spin-orbit torque and the unidirectional magnetoresistance. We also emphasize that the unidirectional magnetoresistance has not only longitudinal but also transverse components in the electric field: current indices which complicate its separation from the thermoelectric contributions to the detected signals in common experimental techniques. We use the theoretical results to analyze our measurements of the on-resonance and off-resonance mixing signals in microbar devices fabricated from an epitaxial NiMnSb film along different crystal directions. Based on the analysis we extract an experimental estimate of the unidirectional magnetoresistance in NiMnSb.
Endothelium homeostasis alterations govern the pathogenesis of cardiovascular diseases. Several studies show that vitamins anti-oxidant proprieties rescue the endothelial functions adversely affected ...by oxidative stress in several diseases. We investigated the vitamin D anti-oxidant potential in human endothelial cells exposed to H
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oxidative stress. Vitamin D protected endothelial cells against H
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oxidative stress counteracting the superoxide anion generation, the apoptosis and blocking the extrinsic caspase cascade by positively controlling phospho-active ERKs level. MEKs/ERKs inhibitor U0126 reverted the vitamin D anti-oxidant effects. Characterizing the vitamin D downstream effector, we found that vitamin D up-regulated SirT-1 and reverted the SirT-1 down-regulation induced by H
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. ERKs activation by vitamin D strictly correlated with SirT-1 protein accumulation since both MEKs/ERKs inhibition and ERK1/2 silencing decreased SIRT-1. SirT-1 inhibition by Sirtinol reverted the vitamin D anti-oxidant effects. Thus, vitamin D significantly reduced the endothelial malfunction and damage caused by oxidative stress, through the activation of MEKs/ERKs/SirT-1 axis.
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