36 research outputs found
Anomalous sign inversion of spin-orbit torque in ferromagnetic/nonmagnetic bilayer systems due to self-induced spin-orbit torque
Self-induced spin-orbit torques (SI-SOTs) in ferromagnetic (FM) layers have
been overlooked when estimating the spin Hall angle (SHA) of adjacent
nonmagnetic (NM) layers. In this work, we observe anomalous sign inversion of
the total SOT in the spin-torque ferromagnetic resonance due to the enhanced
SI-SOT, and successfully rationalize the sign inversion through a theoretical
calculation considering the SHE in both the NM and FM layers. The findings show
that using an FM layer whose SHA sign is the same as that of the NM achieves
efficient SOT-magnetization switching with the assistance of the SI-SOT. The
contribution of the SI-SOT becomes salient for a weakly conductive NM layer,
and conventional analyses that do not consider the SI-SOT can overestimate the
SHA of the NM layer by a factor of more than 150.Comment: 9 pages, 4 figure
Enhancement of low-frequency spin-orbit-torque ferromagnetic resonance signals by frequency tuning observed in Pt/Py, Pt/Co, and Pt/Fe bilayers
DC voltages via spin rectification effect (SRE), VDC, under microwave irradiation are investigated for three platinum (Pt)/ferromagnetic metal (FM) bilayer structures: Pt/Ni₈₀Fe₂₀, Pt/Co, and Pt/Fe. At the microwave frequency region lower than the resonant frequency, large VDC is obtained at zero DC magnetic field for all devices. In frequency dependence just around the resonant frequency, sharp rise and drop of magnitude in VDC are observed. These behaviors are well explained by the numerically calculated magnetic susceptibility. It is also found that the magnitude of VDC is strongly dependent on the slope of magnetoresistance spectrum. These findings lead to developments of sensitive detection technique for nano-scale magnetization switching
Gigantic Anisotropy of Self-Induced Spin-Orbit Torque in Weyl Ferromagnet Co2MnGa
Spin-orbit torque (SOT) is receiving tremendous attention from both
fundamental and application-oriented aspects. Co2MnGa, a Weyl ferromagnet that
is in a class of topological quantum materials, possesses cubic-based high
structural symmetry, the L21 crystal ordering, which should be incapable of
hosting anisotropic SOT in conventional understanding. Here we show the
discovery of a gigantic anisotropy of self-induced SOT in Co2MnGa. The
magnitude of the SOT is comparable to that of heavy metal/ferromagnet bilayer
systems despite the high inversion symmetry of the Co2MnGa structure. More
surprisingly, a sign inversion of the self-induced SOT is observed for
different crystal axes. This finding stems from the interplay of the
topological nature of the electronic states and their strong modulation by
external strain. Our research enriches the understanding of the physics of
self-induced SOT and demonstrates a versatile method for tuning SOT
efficiencies in a wide range of materials for topological and spintronic
devices.Comment: 15pages, 4figures (To appear Nano Lett.
Observation of gigantic spin conversion anisotropy in bismuth
Whilst the g-factor can be anisotropic due to the spin-orbit interaction
(SOI), its existence in solids cannot be simply asserted from a band structure,
which hinders progress on studies from such the viewpoints. The g-factor in
bismuth (Bi) is largely anisotropic; especially for holes at T-point, the
g-factor perpendicular to the trigonal axis is negligibly small (< 0.112),
whereas the g-factor along the trigonal axis is very large (62.7). We clarified
in this work that the large g- factor anisotropy gives rise to the gigantic
spin conversion anisotropy in Bi from experimental and theoretical approaches.
Spin-torque ferromagnetic resonance was applied to estimate the spin conversion
efficiency in rhombohedral (110) Bi to be 17%, which is unlike the negligibly
small efficiency in Bi(111). Harmonic Hall measurements supports the large spin
conversion efficiency in Bi(110). This is the first observation of gigantic
spin conversion anisotropy as the clear manifestation of the g-factor
anisotropy. Beyond the emblematic case of Bi, our study unveiled the
significance of the g-factor anisotropy in condensed-matter physics and can
pave a pathway toward establishing novel spin physics under g-factor control.Comment: 28 pages, 7 figure
A new era of therapeutic strategies for chronic thromboembolic pulmonary hypertension by two different interventional therapies; pulmonary endarterectomy and percutaneous transluminal pulmonary angioplasty.
BACKGROUND: Pulmonary endarterectomy (PEA) is established for the treatment of chronic thromboembolic pulmonary hypertension (CTEPH). Recently, percutaneous transluminal pulmonary angioplasty (PTPA) has been added for peripheral-type CTEPH, whose lesions exist in segmental, subsegmental, and more distal pulmonary arteries. A shift in clinical practice of interventional therapies occurred in 2009 (first mainly PEA, later PTPA). We examined the latest clinical outcomes of patients with CTEPH. METHODS AND RESULTS: This study retrospectively included 136 patients with CTEPH. Twenty-nine were treated only with drug (Drug-group), and the other 107 underwent interventional therapies (Interventions-group) (39 underwent PEA [PEA-group] and 68 underwent PTPA [PTPA-group]). Total 213 PTPA sessions (failures, 0%; mortality rate, 1.47%) was performed in the PTPA-group (complications: reperfusion pulmonary edema, 7.0%; hemosputum or hemoptysis, 5.6%; vessel dissection, 2.3%; wiring perforation, 0.9%). Although baseline hemodynamic parameters were significantly more severe in the Interventions-group, the outcome after the diagnosis was much better in the Interventions-group than in the Drug-group (98% vs. 64% 5-year survival, p<0.0001). Hemodynamic improvement in the PEA-group was a 46% decrease in mean pulmonary arterial pressure (PAP) and a 49% decrease in total pulmonary resistance (TPR) (follow-up period; 74.7 ± 32.3 months), while those in the PTPA-group were a 40% decrease in mean PAP and a 49% decrease in TPR (follow-up period; 17.4 ± 9.3 months). The 2-year survival rate in the Drug-group was 82.0%, and the 2-year survival rate, occurrence of right heart failure, and re-vascularization rate in the PEA-group were 97.4%, 2.6%, and 2.8%, and those in the PTPA-group were 98.5%, 2.9%, and 2.9%, respectively. CONCLUSION: The patients who underwent interventional therapies had better results than those treated only with drugs. The availability of both of these operative and catheter-based interventional therapies leads us to expect the dawn of a new era of therapeutic strategies for CTEPH
All‐Electric Spin Device Operation Using the Weyl Semimetal, WTe2, at Room Temperature
Abstract Topological quantum materials (TQMs) possess abundant and attractive spin physics, and a Weyl semimetal is the representative material because of the generation of spin polarization that is available for spin devices due to its Weyl nature. Meanwhile, a Weyl semimetal allows the other but unexplored spin polarization due to local symmetry breaking. Here, all‐electric spin device operation using a type‐II Weyl semimetal, WTe2, at room temperature is reported. The polarization of spins propagating in the all‐electric device is perpendicular to the WTe2 plane, which is ascribed to local in‐plane symmetry breaking in WTe2, yielding the spin polarization creation of propagating charged carriers, namely, the spin‐polarized state creation from the nonpolarized state. Systematic control experiments unequivocally negate unexpected artifacts, such as the anomalous Hall effect, the anisotropic magnetoresistance, etc. Creation of all‐electric spin devices made of TQMs and their operation at room temperature can pave a new pathway for novel spin devices made of TQMs resilient to thermal fluctuation