32 research outputs found
Direct observation of spin-quadrupolar excitations in SrCoGeO by high field ESR
Exotic spin-multipolar ordering in spin transition metal insulators has so
far eluded unambiguous experimental observation. A less studied, but perhaps
more feasible fingerprint of multipole character emerges in the excitation
spectrum in the form of quadrupolar transitions. Such multipolar excitations
are desirable as they can be manipulated with the use of light or electric
field and can be captured by means of conventional experimental techniques.
Here we study single crystals of multiferroic SrCoGeO, and show
that due to its nearly isotropic nature a purely quadrupolar bimagnon mode
appears in the electron spin resonance (ESR) spectra. This non-magnetic
spin-excitation couples to the electric field of the light and becomes
observable for a specific experimental configuration, in full agreement with a
theoretical analysis of the selection rules.Comment: 19 pages, 13 figures, , accepted for publication in Phys. Rev.
Spin-orbit torque generation in bilayers composed of CoFeB and epitaxial SrIrO grown on an orthorhombic DyScO substrate
We report on the highly efficient spin-orbit torque (SOT) generation in
epitaxial SrIrO(SIO), which is grown on an orthorhombic DyScO(110)
substrate. By conducting harmonic Hall measurement in
CoFeB (CoFeB)/SIO bilayers, we characterize two kinds of
the SOTs, i.e., dampinglike (DL) and fieldlike ones to find that the former is
much larger than the latter. By comparison with the Pt control sample with the
same CoFeB thickness, the observed DL SOT efficiency of SIO
(0.32) is three times higher than that of Pt (0.093). The
is nearly constant as a function of the CoFeB thickness,
suggesting that the SIO plays a crucial role in the large SOT generation. These
results on the CoFeB/SIO bilayers highlight that the epitaxial SIO is promising
for low-current and reliable spin-orbit torque-controlled devices.Comment: arXiv admin note: text overlap with arXiv:2305.1788
Spin current generation from an epitaxial tungsten dioxide WO
We report on efficient spin current generation at room temperature in rutile
type WO grown on AlO(0001) substrate. The optimal WO
film has (010)-oriented monoclinically distorted rutile structure with metallic
conductivity due to 5 electrons, as characterized by x-ray
diffraction, electronic transport, and x-ray photoelectron spectroscopy. By
conducting harmonic Hall measurement in NiFe/WO bilayer, we
estimate two symmetries of the spin-orbit torque (SOT), i.e., dampinglike (DL)
and fieldlike ones to find that the former is larger than the latter. By
comparison with the NiFe/W control sample, the observed DL SOT
efficiency of WO (+0.174) is about two thirds of that of W
(-0.281) in magnitude, with a striking difference in their signs. The magnitude
of the of WO exhibits comparable value to those of widely
reported Pt and Ta, and Ir oxide IrO. The positive sign of the
of WO can be explained by the preceding theoretical study
based on the 4 oxides. These results highlight that the epitaxial
WO offers a great opportunity of rutile oxides with spintronic
functionalities, leading to future spin-orbit torque-controlled devices.Comment: 14 pages, 4 figure
Quantum gapped state in a spin-1/2 distorted honeycomb-based lattice with frustration
We successfully synthesized (-Py-V)[Cu(hfac)], a verdazyl-based
complex. Molecular orbital calculations revealed five types of intermolecular
interactions between the radical spins and two types of intramolecular
interactions between the radical and the Cu spins, resulting in a spin-1/2
distorted honeycomb-based lattice. Additionally, competing ferromagnetic and
antiferromagnetic (AF) interactions induce frustration. The magnetization curve
displayed a multistage increase, including a zero-field energy gap. Considering
the stronger AF interactions that form dimers and tetramers, the magnetic
susceptibility and magnetization curves were qualitatively explained. These
findings demonstrated that the quantum state, based on the dominant AF
interactions, was stabilized due to the effects of frustration in the lattice.
Hence, the exchange interactions forming two-dimensional couplings decoupled,
reducing energy loss caused by frustration and leading to frustration-induced
dimensional reduction.Comment: 6 pages, 5 figure
Field-induced quantum phase in a frustrated zigzag-square lattice
This study presents the experimental realization of a spin-1/2 zigzag-square
lattice in a verdazyl-based complex, namely
(-Py-V-2,6-F)Cu(hfac). Molecular orbital calculations suggest
the presence of five types of frustrated exchange couplings. Our observations
reveal an incremental increase in the magnetization curve beyond a critical
field, signifying a phase transition from the antiferromagnetic ordered state
to a quantum state characterized by a 1/2 plateau. This intriguing behavior
arises from the effective stabilization of a zigzag chain by the external
fields. These results provide evidence for field-induced dimensional reduction
in a zigzag-square lattice attributed to the effects of frustration.Comment: 5 pages, 4 figure