Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures

We study the spin-orbit torque (SOT) effective fields in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO magnetic heterostructures using the adiabatic harmonic Hall measurement. High-quality perpendicular-magnetic-anisotropy CoFeAl layers were grown on Cr and Ru layers. The magnitudes of the SOT effective fields were found to significantly depend on the underlayer material (Cr or Ru) as well as their thicknesses. The damping-like longitudinal effective field ({\Delta}H_L) increases with increasing underlayer thickness for all heterostructures. In contrast, the field-like transverse effective field ({\Delta}H_T) increases with increasing Ru thickness while it is almost constant or slightly decreases with increasing Cr thickness. The sign of {\Delta}H_L observed in the Cr-underlayer devices is opposite from that in the Ru-underlayer devices while {\Delta}H_T shows the same sign with a small magnitude. The opposite directions of {\Delta}HL indicate that the signs of spin Hall angle in Cr and Ru are opposite, which are in good agreement with theoretical predictions. These results show sizable contribution from SOT even for elements with small spin orbit coupling such as 3d Cr and 4d Ru.Comment: 10 pages, 5 figures, AIP Advances 201

Composite metamaterials with dual-band magnetic resonances in the terahertz frequency regime

Composite metamaterials(CMMs) combining a subwavelength metallic hole array (i.e. one-layer fishnet structure) and an array of split-ring resonators(SRRs) on the same board are fabricated with gold films on silicon wafer. Transmission measurements of the CMMs in the terahertz range have been performed. Dual-band magnetic resonances, namely, a LC resonance at 4.40 THz and an additional magnetic resonance at 8.64 THz originating from the antiparallel current in wire pairs in the CMMs are observed when the electrical field polarization of the incident light is parallel to the gap of the component SRR. The numerical simulations agree well with the experimental results and further clarify the nature of the dual-band magnetic resonances.Comment: 4 figures, 14 page

Fully epitaxial fcc(111) magnetic tunnel junctions with a Co90Fe10/MgAlO/Co90Fe10 structure

Magnetic tunnel junctions (MTJs) with bcc(001)-type structures such as Fe(001)/MgO(001)/Fe(001), have been widely used as the core of various spintronic devices such as magnetoresistive memories; however, the limited material selection of (001)-type MTJs hinders the further development of spintronic devices. Here, as an alternative to the (001)-type MTJs, an fcc(111)-type MTJ using a fully epitaxial CoFe/rock-salt MgAlO (MAO)/CoFe is explored to introduce close-packed lattice systems into MTJs. Using an atomically flat Ru(0001) epitaxial buffer layer, fcc(111) epitaxial growth of the CoFe/MAO/CoFe trilayer is achieved. Sharp CoFe(111)/MAO(111) interfaces are confirmed due to the introduction of periodic dislocations by forming a 5:6 in-plane lattice matching structure. The fabricated (111) MTJ exhibits a tunnel magnetoresistance ratio of 37% at room temperature (47% at 10 K). Symmetric differential conductance curves with respect to bias polarity are observed, indicating the achievement of nearly identical upper and lower MAO interface qualities. Despite the charge-uncompensated (111) orientation for a rock-salt-like MAO barrier, the achievement of flat, stable, and spin-polarized barrier interfaces opens a promising avenue for expanding the design of MTJ structures.Comment: 18 pages, 5 figure

Influence of Intrinsic Electronic Properties on Light Transmission through Subwavelength Holes on Gold and MgB2 Thin Films

We show how intrinsic material properties modify light transmission through subwavelength hole arrays on thin metallic films in the THz regime. We compare the temperature-dependent transmittance of Au films and MgB$_{2}$ films. The experimental data is consistent with analytical calculations, and is attributed to the temperature change of the conductivity of both films. The transmission versus conductivity is interpreted within the open resonator model when taking the skin depth into consideration. We also show that the efficiency of this temperature control depends on the ratio of the transmission peak frequency to the superconducting energy gap in MgB$_{2}$ films.Comment: 6 pages, 6 figure