RESUMEN
Spin current, converted from charge current via spin Hall or Rashba effects, can transfer its angular momentum to local moments in a ferromagnetic layer. In this regard, the high charge-to-spin conversion efficiency is required for magnetization manipulation for developing future memory or logic devices including magnetic random-access memory. Here, the bulk Rashba-type charge-to-spin conversion is demonstrated in an artificial superlattice without centrosymmetry. The charge-to-spin conversion in [Pt/Co/W] superlattice with sub-nm scale thickness shows strong W thickness dependence. When the W thickness becomes 0.6 nm, the observed field-like torque efficiency is about 0.6, which is an order larger than other metallic heterostructures. First-principles calculation suggests that such large field-like torque arises from bulk-type Rashba effect due to the vertically broken inversion symmetry inherent from W layers. The result implies that the spin splitting in a band of such an ABC-type artificial SL can be an additional degree of freedom for the large charge-to-spin conversion.
RESUMEN
Antiferromagnetic spintronics is an emerging research field which aims to utilize antiferromagnets as core elements in spintronic devices. A central motivation towards this direction is that antiferromagnetic spin dynamics is expected to be much faster than its ferromagnetic counterpart. Recent theories indeed predicted faster dynamics of antiferromagnetic domain walls (DWs) than ferromagnetic DWs. However, experimental investigations of antiferromagnetic spin dynamics have remained unexplored, mainly because of the magnetic field immunity of antiferromagnets. Here we show that fast field-driven antiferromagnetic spin dynamics is realized in ferrimagnets at the angular momentum compensation point TA. Using rare earth-3d-transition metal ferrimagnetic compounds where net magnetic moment is nonzero at TA, the field-driven DW mobility is remarkably enhanced up to 20 km s-1 T-1. The collective coordinate approach generalized for ferrimagnets and atomistic spin model simulations show that this remarkable enhancement is a consequence of antiferromagnetic spin dynamics at TA. Our finding allows us to investigate the physics of antiferromagnetic spin dynamics and highlights the importance of tuning of the angular momentum compensation point of ferrimagnets, which could be a key towards ferrimagnetic spintronics.
RESUMEN
Zinc oxide (ZnO) nanocomposites have been widely applied in biomedical fields due to their multifunctionality and biocompatibility. However, the physicochemical properties of ZnO nanocomposite involved in nano-bio interactions are poorly defined. To assess the potential applicability of ZnO nanowires for intracellular delivery of biomolecules, we examined the dynamics of cellular activity of cells growing on densely packed ZnO nanowire arrays with two different physical conformations, vertical (VNW) or fan-shaped (FNW) nanowires. Although a fraction of human embryonic kidney cells cultured on VNW or FNW underwent rapid apoptosis, peaking at 6 h after incubation, cells could survive and replicate without significant apoptosis on the foreign substrate after 12 h of lag phase. In addition, the cells formed lamellipodia to wrap FNW, and efficiently took up peptides non-covalently coated on VNW and FNW within 30 min of incubation. Moreover, FNW could mediate intracellular delivery of associated DNAs and their gene expression, suggesting that ZnO nanowires transiently penetrate membranes to mediate intranuclear delivery of exogenous DNA. These results indicate that ZnO nanowire arrays can serve as nanocomposites for manipulating nano-bio interfaces if appropriately modified in a 3-dimensional conformation.
