Synthetic Rashba spin-orbit system using a silicon metal-oxide semiconductor.

The spin-orbit interaction (SOI), mainly manifesting itself in heavy elements and compound materials, has been attracting much attention as a means of manipulating and/or converting a spin degree of freedom. Here, we show that a Si metal-oxide- semiconductor (MOS) heterostructure possesses Rashba-type SOI, although Si is a light element and has lattice inversion symmetry resulting in inherently negligible SOI in bulk form. When a strong gate electric field is applied to the Si MOS, we observe spin lifetime anisotropy of propagating spins in the Si through the formation of an emergent effective magnetic field due to the SOI. Furthermore, the Rashba parameter α in the system increases linearly up to 9.8 × 10-16 eV m for a gate electric field of 0.5 V nm-1; that is, it is gate tuneable and the spin splitting of 0.6 µeV is relatively large. Our finding establishes a family of spin-orbit systems.

Uncooled sub-GHz spin bolometer driven by auto-oscillation.

Bolometers are rectification devices that convert electromagnetic waves into direct current voltage through a temperature change. A superconducting bolometer has a responsivity of approximately 106-107 V/W under cryogenic temperatures at infrared wavelengths; however, no devices have realized such a high responsivity in the sub-GHz frequency region. We describe a spin bolometer with a responsivity of (4.40 ± 0.04) × 106 V/W in the sub-GHz region at room temperature using heat generated in magnetic tunnel junctions through auto-oscillation. We attribute the unexpectedly high responsivity to a heat-induced spin-torque. This spin-torque modulates and synchronizes the magnetization precession due to the spin-torque auto-oscillation and produces a large voltage output. In our device, heat-induced spin-torque was obtained because of a large heat-controlled magnetic anisotropy change: -2.7 µJ/Wm, which is significant for enhancing dynamic range and responsivity. This study can potentially lead to the development of highly sensitive microwave detectors in the sub-GHz region.

Control of Spin-Orbit Torques by Interface Engineering in Topological Insulator Heterostructures.

(Bi1-xSbx)2Te3 topological insulators (TIs) are gathering increasing attention owing to their large charge-to-spin conversion efficiency and the ensuing spin-orbit torques (SOTs) that can be used to manipulate the magnetization of a ferromagnet (FM). The origin of the torques, however, remains elusive, while the implications of hybridized states and the strong material intermixing at the TI/FM interface are essentially unexplored. By combining interface chemical analysis and spin-transfer ferromagnetic resonance (ST-FMR) measurements, we demonstrate that intermixing plays a critical role in the generation of SOTs. By inserting a suitable normal metal spacer, material intermixing is reduced and the TI properties at the interface are largely improved, resulting in strong variations in the nature of the SOTs. A dramatic enhancement of a field-like torque, opposing and surpassing the Oersted-field torque, is observed, which can be attributed to the non-equilibrium spin density in Rashba-split surface bands and to the suppression of spin memory loss. These phenomena can play a relevant role at other interfaces, such as those comprising transition metal dichalcogenides.

Enhanced electric control of magnetic anisotropy via high thermal resistance capping layers in magnetic tunnel junctions.

We studied nonlinear magnetic anisotropy changes to the DC bias voltage of magnetic tunnel junctions (MTJs) with capping layers of different thermal resistances. We found that increasing the thickness of MgO capping layers (in the range 0.3-0.5 nm) in MTJs enhances the Joule heating-induced magnetic anisotropy change, which indicates an enhancement of the interfacial thermal resistance at the FeB|MgO capping layer interface. This enhanced interfacial thermal resistance may be attributed to roughness at the FeB|MgO interface. Moreover, we observed a larger power-driven magnetic anisotropy change of 3.21 µJ W-1m-1 in the MTJ with a composite MgO (0.3 nm)|W (2 nm)|MgO (0.4 nm) capping layer. This research supports methods of efficient spin manipulation of spintronic devices such as microwave devices and magnetic memories.

Detection and isolation of protein susceptible indigenous bacteria affected by dietary milk-casein, albumen and soy-protein in the caecum of ICR mice.

In this study, we fed ICR mice with a high-sucrose diet containing 20% w/w of milk-casein (MC), egg-white (EW), or soy-protein (SP) for 14 days in order to detect the presence of protein-susceptible gut indigenous bacteria (P-SIB). The caecal microbiome was examined by 16S rDNA amplicon sequencing using a next-generation MiSeq system. Principal coordinate analysis of the operational taxonomic units (OTUs) revealed that the microbiomes differed among the three groups. Typical SIB found in the MC-fed group were Bacteroides acidifaciens-, Bacteroides sartorii-, Eisenbergiella sp., and Lachnospiraceae sp.-like; in the EW-fed group were Lactobacillus murinus and Enterococcus faecium/avium-like; and in the SP-fed group were Muribaculaceae sp.-like bacteria. We also found that a few Lachnospiraceae sp.- and Clostridium disporicum-like bacteria were suppressed in the EW-fed mice. Out of the P-SIB detected, B. acidifaciens, L. murinus, E. faecium, and E. avium could be isolated and identified using BL agar and 16S rDNA BLAST search, respectively.

Microwave amplification in a magnetic tunnel junction induced by heat-to-spin conversion at the nanoscale.

Heat-driven engines are hard to realize in nanoscale machines because of efficient heat dissipation1. However, in the realm of spintronics, heat has been employed successfully-for example, heat current has been converted into a spin current in a NiFe|Pt bilayer system2, and Joule heating has enabled selective writing in magnetic memory arrays3. Here, we use Joule heating in nanoscale magnetic tunnel junctions to create a giant spin torque due to a magnetic anisotropy change. Efficient conversion from heat dynamics to spin dynamics is obtained because of a large interfacial thermal resistance at an FeB|MgO interface. The heat-driven spin torque is equivalent to a voltage-controlled magnetic anisotropy4,5 of approximately 300 fJ V-1 m-1, which is more than twice the value reported in a (Co)FeB|MgO system6,7. We demonstrate an electric microwave amplification gain of 20% in a d.c. biased magnetic tunnel junction as a result of this spin torque. While electric d.c. power amplification in spintronic devices has been realized previously8, the microwave amplification was limited to relatively small amplification gains (G = radiofrequency output voltage/radiofrequency input voltage) and has never exceeded 1 (refs 9-13). A magnetic tunnel junction driven by radiofrequency spin transfer torque using ferromagnetic resonance enabled a relatively large gain of G ≈ 0.55 (ref. 12). Furthermore, radiofrequency spin waves were tuned by the spin transfer effect14,15. The heat-driven giant spin torque in the FeB|MgO16,17 magnetic tunnel junction, which shows a large magnetization precession and resistance oscillation under a d.c. bias, overcomes the above limitations and provides a gain larger than 1.

Voltage-Controlled Magnetic Anisotropy in Fe1-xCox/Pd/MgO system.

Voltage-controlled magnetic anisotropy (VCMA) in an epitaxially grown Fe/Fe1-xCox/Pd/MgO system was investigated using spin-wave spectroscopy. The spin-wave resonant frequency linearly depended on the bias-voltage. The resonant-frequency shift increased with the Co fraction in Fe1-xCox/Pd. We achieved a VCMA of approximately 250 fJ/Vm at the Co/Pd/MgO region.

Voltage controlled interfacial magnetism through platinum orbits.

Electric fields at interfaces exhibit useful phenomena, such as switching functions in transistors, through electron accumulations and/or electric dipole inductions. We find one potentially unique situation in a metal-dielectric interface in which the electric field is atomically inhomogeneous because of the strong electrostatic screening effect in metals. Such electric fields enable us to access electric quadrupoles of the electron shell. Here we show, by synchrotron X-ray absorption spectroscopy, electric field induction of magnetic dipole moments in a platinum monatomic layer placed on ferromagnetic iron. Our theoretical analysis indicates that electric quadrupole induction produces magnetic dipole moments and provides a large magnetic anisotropy change. In contrast with the inability of current designs to offer ultrahigh-density memory devices using electric-field-induced spin control, our findings enable a material design showing more than ten times larger anisotropy energy change for such a use and highlight a path in electric-field control of condensed matter.