arXiv subjects

Y. Onose

Publications and source records attributed to Y. Onose.

At least 19 recordsLinked to original sources

arXiv2024

Magnetic structure of the noncentrosymmetric magnet Sr2MnSi2O7 through irreducible representation and magnetic space group analyses

Magnetic structures of the noncentrosymmetric magnet Sr$_2$MnSi$_2$O$_7$ were examined through neutron diffraction for powder and single-crystalline samples, as well as magnetometry measurements. All allowed magnetic structures under the space group $P\bar{4}2_1 m$ with the magnetic wavevector $\vec{q}_{\rm m}=(0,0,1/2)$~r.l.u., were analysed via irreducible representation and magnetic space group approaches. The compound is refined to have in-plane magnetic moments within the magnetic space group $Cmc2_1.1^{\prime}_c$ (\#36.177) under zero field, which can be altered to $P2_1 2_1 2_1.1^{\prime}_c$ (\#19.28) above $\mu_0 H=0.067(5)$~T to align induced weak-ferromagnetic components within one layer on the $ab$-plane. All refined parameters are provided following the recent framework based upon the magnetic space group, which better conveys when exchanging crystallographic information for commensurate magnetic structures.

cond-mat.str-el↗

arXiv2021

Elastic study of electric quadrupolar correlation in the paramagnetic state of a frustrated quantum magnet $\rm Tb_{2+\it δ}Ti_{2-\it δ}O_7$

Electric quadrupolar state in a frustrated quantum magnet $\rm Tb_{2+\it δ}Ti_{2-\it δ}O_7$ has been studied by means of ultrasonic and magnetostriction measurements. A single crystal showed elastic anomaly at about 0.4 K, manifesting a long-range quadrupole ordering. By investigating anisotropy of the magnetoelastic responses, we found a crossover temperature for the strongly correlated quadrupole state, below which the experimental data of elastic constant and magnetostriction become qualitatively different from their calculations based on a single-ion model. We suppose that relatively high onset temperature of the quadrupole correlation compared with the transition temperature is ascribed to the geometrical frustration effect, and this correlated state seems to be responsible for the unusual properties in the paramagentic state of $\rm Tb_2Ti_2O_7$.

cond-mat.str-el↗

arXiv2020

Chirality memory stored in magnetic domain walls in the ferromagnetic state of MnP

Chirality in a helimagnetic structure is determined by the sense of magnetic moment rotation. We found that the chiral information did not disappear even after the phase transition to the high-temperature ferromagnetic phase in a helimagnet MnP. The 2nd harmonic resistivity $ρ^{\rm 2f}$, which reflects the breaking down of mirror symmetry, was found to be almost unchanged after heating the sample above the ferromagnetic transition temperature and cooling it back to the helimagnetic state. The application of a magnetic field along the easy axis in the ferromagnetic state quenched the chirality-induced $ρ^{\rm 2f}$. This indicates that the chirality memory effect originated from the ferromagnetic domain walls.

cond-mat.str-el↗

arXiv2020

Magnetization control by angular momentum transfer from surface acoustic wave to ferromagnetic spin moments

The angular momentum interconversion between electron spin and other type of angular momenta is useful to develop new spintronic functionalities. The conversions from the angular momentum of photon and mechanical rotation to ferromagnetic spin moment have been well studied. While the recent studies theoretically suggested circular vibration of atoms works as angular momentum of phonon, the direct experimental demonstration of conversion to spin moments remains to be performed. Here we demonstrate that the phonon angular momentum of surface acoustic wave can control the magnetization of a ferromagnetic Ni film by means of the phononic-to-electronic conversion of angular momentum in Ni/LiNbO$_3$ hybrid device. This result clearly shows the phonon angular momentum is useful to further fictionalize spintronic devices.

cond-mat.mes-hall↗

arXiv2019

Electric current control of spin helicity in an itinerant helimagnet

Chirality is breaking of mirror symmetry in matter. In the fields of biology and chemistry, this is particularly important because some of the essential molecules in life such as amino acids and DNA have chirality. It is a long-standing mystery how one of the enantiomers was chosen at the beginning stage of life. The understanding of the emergence of homochirality under some conditions is indispensable for the study of the origin of life as well as pharmaceutical science. The chirality is also emergent in magnetic structures. The longitudinal helical magnetic structure is the chiral object composed of magnetic moments, in which the ordered direction of the magnetic moment spatially rotates in the plane perpendicular to the propagation vector (Fig. 1a). Since the sense of rotation, which is denoted as helicity, is reversed by any mirror operation, it is corresponding to the chirality. Here we show that the chirality of a longitudinal helical structure can be controlled by the magnetic field and electric current owing to the spin-transfer torque irrelevant to the spin-orbit interaction and probed by electrical magnetochiral effect, which is sensitive to the chiral symmetry breaking, in an itinerant helimagnet MnP. This phenomenon is distinct from the multiferroicity in transverse-type insulating helical magnets, in which the helical plane is parallel to the propagation vector, because the magnetic structure has polar symmetry not chiral one. While the combination of the magnetic field and electric current satisfies the symmetrical rule of external stimulus for the chirality control, the control with them was not reported for any chiral object previously. The present result may pave a new route to the control of chiralities originating from magnetic and atomical arrangements.

cond-mat.str-el↗

arXiv2018

Surface acoustic wave coupled to magnetic resonance on a multiferroic CuB$_2$O$_4$

We observed surface acoustic wave (SAW) propagation on a multiferroic material CuB$_2$O$_4$ with use of two interdigital transducers (IDTs). The period of IDT fingers is as short as 1.6 $μ$m so that the frequency of SAW is 3 GHz, which is comparable with that of magnetic resonance. In antiferromagnetic phase, the SAW excitation intensity varied with the magnitude and direction of the magnetic field, owing to the dynamical coupling between SAWs and antiferromagnetic resonance of CuB$_2$O$_4$. The microscopic mechanism is discussed based on the symmetrically allowed magentoelastic coupling.

cond-mat.mes-hall↗

arXiv2018

Microwave non-reciprocity of magnon excitations in a non-centrosymmetric antiferromagnet Ba$_2$MnGe$_2$O$_7$

We have investigated the microwave non-reciprocity for a non-centrosymmetric antiferromagnet Ba$_2$MnGe$_2$O$_7$. The magnon modes expected by the conventional spin wave theory for staggered antiferromagnets are certainly observed. The magnitudes of exchange interaction and magnetic anisotropy are obtained by the comparison with the theory. The microwave non-reciprocity is identified for one of these mode. The relative magnitude of microwave non-reciprocity can be explained with use of spin wave theory and Kubo formula.

cond-mat.mtrl-sci↗

arXiv2017

Magnetotransport properties in a noncentrosymmetric itinerant magnet Cr$_{11}$Ge$_{19}$

We have investigated anomalous Hall effect and magnetoresistance in a noncentrosymmetric itinerant magnet Cr$_{11}$Ge$_{19}$. While the temperature- and magnetic-field-dependent anomalous Hall conductivity is just proportional to the magnetization above 30 K, it is more enhanced in the lower temperature region. The magnitude of negative magnetoresistance begins to increase toward low temperature around 30 K. The anisotropic magnetoresistance emerges at similar temperature. Because there is no anomaly in the temperature dependence of magnetization around 30 K, the origin of these observations in transport properties is ascribed to some electronic structure with the energy scale of 30 K. We speculate this is caused by the spin splitting due to breaking of spatial inversion symmetry.

cond-mat.str-el↗

arXiv2017

Universality of the helimagnetic transition in cubic chiral magnets: Small angle neutron scattering and neutron spin echo spectroscopy studies of Fe$_{1-x}$Co$_x$Si

We present a comprehensive Small Angle Neutron Scattering (SANS) and Neutron Spin Echo Spectroscopy (NSE) study of the structural and dynamical aspects of the helimagnetic transition in Fe$_{1-x}$Co$_x$Si with $x$ = 0.30. In contrast to the sharp transition observed in the archetype chiral magnet MnSi, the transition in Fe$_{1-x}$Co$_x$Si is gradual and long-range helimagnetic ordering coexists with short-range correlations over a wide temperature range. The dynamics are more complex than in MnSi and involve long relaxation times with a stretched exponential relaxation which persists even under magnetic field. These results in conjunction with an analysis of the hierarchy of the relevant length scales show that the helimagnetic transition in Fe$_{1-x}$Co$_x$Si differs substantially from the transition in MnSi and question the validity of a universal approach to the helimagnetic transition in chiral magnets.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic relaxation phenomena in the Chiral Magnet Fe$_{1-x}$Co$_x$Si: An ac susceptibility study

We present a systematic study of the ac susceptibility of the chiral magnet Fe$_{1-x}$Co$_x$Si with $x$ = 0.30 covering four orders of magnitude in frequencies from 0.1 Hz to 1 kHz, with particular emphasis to the pronounced history dependence. Characteristic relaxation times ranging from a few milliseconds to tens of seconds are observed around the skyrmion lattice A-phase, the helical-to-conical transition and in a region above $T_C$. The distribution of relaxation frequencies around the A-phase is broad, asymmetric and originates from multiple coexisting relaxation processes. The pronounced dependence of the magnetic phase diagram on the magnetic history and cooling rates as well as the asymmetric frequency dependence and slow dynamics suggest more complicated physical phenomena in Fe$_{0.7}$Co$_{0.3}$Si than in other chiral magnets.

cond-mat.mtrl-sci↗

arXiv2016

Extended skyrmion lattice scattering and long-time memory in the chiral magnet Fe$_{1-x}$Co$_x$Si

Small angle neutron scattering measurements on a bulk single crystal of the doped chiral magnet Fe$_{1-x}$Co$_x$Si with $x$=0.3 reveal a pronounced effect of the magnetic history and cooling rates on the magnetic phase diagram. The extracted phase diagrams are qualitatively different for zero and field cooling and reveal a metastable skyrmion lattice phase outside the A-phase for the latter case. These thermodynamically metastable skyrmion lattice correlations coexist with the conical phase and can be enhanced by increasing the cooling rate. They appear in a wide region of the phase diagram at temperatures below the $A$-phase but also at fields considerably smaller or higher than the fields required to stabilize the A-phase.

cond-mat.mtrl-sci↗

arXiv2016

Magnetoelectrical control of nonreciprocal microwave response in a multiferroic helimagnet

Control of physical property in terms of external fields is essential for contemporary technologies. The conductance can be controlled by a gate electric field in a field effect transistor, which is a main component of the integrated circuit. Optical phenomena induced by an electric field such as electroluminescence and electrochromism are useful for display and other technologies. Control of microwave propagation seems also imperative for future wireless communication technology. Microwave properties in solids are dominated mostly by magnetic excitations, which cannot be easily controlled by an electric field. One of the solutions for this problem is utilizing magnetically induced ferroelectrics (multiferroics). Here we show that microwave nonreciprocity, which is difference between oppositely propagating microwaves, can be reversed by the external electric field in a multiferroic helimagnet Ba$_2$Mg$_2$Fe$_{12}$O$_{22}$. This result offers a new avenue for the electrical control of microwave properties.

cond-mat.mtrl-sci↗

arXiv2016

Microwave Magneto-Chiral Effect in a Noncentro-symmetric Magnet CuB2O4

We have investigated microwave nonreciprocity in a noncentro-symmetric magnet CuB2O4. We simultaneously observed differently originated nonreciprocities; the classical magnetic dipolar effect and the magneto-chiral (MCh) effect. By rotating magnetic field in a tetragonal plane, we clearly unveil qualitative difference between them. The MCh effect signal reveals chiral transitions from one enantiomer to the other via intermediate achiral state. We show magnetoelectric effect plays an essential role for the emergence of microwave MCh effect.

cond-mat.mtrl-sci↗

arXiv2016

Nonreciprocal propagation of surface acoustic wave in Ni/LiNbO3

We have investigated surface acoustic wave propagation in Ni/LiNbO$_3$ hybrid devices. We have found the absorption and phase velocity are dependent on the sign of wave vector in a device, which indicates the nonreciprocal propagation characteristic of systems with time reversal and spatial inversion simultaneously broken symmetries. The nonreciprocity is reversed by the 180$^\circ$ rotation of magnetic field. Nonreciprocity seems largely dependent on the shape of ferromagnetic Ni film. The origin of these observations is ascribed to film shape dependent magnetoelastic coupling.

cond-mat.mtrl-sci↗

arXiv2015

Nonreciprocal magnon propagation in a noncentrosymmetric ferromagnet

Relativistic spin-orbit interaction drastically modifies electronic band and endows emergent functionalities. One of the example is the Rashba effect. In noncentrosymmetric systems such as interface and polar materials, the electronic band is spin-splitted depending on the momentum direction owing to the spin-orbit interaction, which is useful for the electric manipulation of spin current. Similar relativistic band-modification is also emergent for spin wave (magnon) in magnetic materials. The asymmetric magnon band dispersion induced by the Dzyaloshinskii-Moriya interaction, which is antisymmetric exchange interaction originating from the spin-orbit interaction, is theoretically expected, and experimentally observed recently in noncentrosymmetric ferromagnets. Here, we demonstrate that the nonreciprocal microwave response can be induced by the asymmetric magnon band in a noncentrosymmetric ferrimagnet LiFe$_5$O$_8$. This result may pave a new path to designing magnonic device based on the relativistic band engineering.

cond-mat.mtrl-sci↗

arXiv2012

Observation of magnetic excitations of skyrmion crystal in a helimagnetic insulator

The skyrmion is a topologically stable spin texture, in which the spin direction wraps a sphere. The topological nature gives rise to emergent electromagnetic phenomena such as topological Hall effect. Recently, the crystallization of nanoscale skyrmions was observed in chiral helimagnets with use of the neutron diffraction and Lorentz transmission electron microscopy. The skyrmions are quite mobile under electric current density as low as $\sim$ 10$^6$ A/m$^2$, and, in some cases, stable up to near room temperature. These features suggest that the skyrmions may work as a magnetic stable-variable similar to the bubble memory but equipped with topological functionalities. Here, we investigate the low-energy excitations of the skyrmion crystal in a helimagnetic insulator Cu$_2$OSeO$_3$ in terms of microwave response. We have observed two distinct excitations of the skyrmion with different polarization characteristics; the counter-clockwise circulating mode at 1 GHz and the breathing mode at 1.5 GHz. These modes may play a crucial role in the low energy dynamics of skyrmions and hence in their manipulation via external stimuli.

cond-mat.mtrl-sci↗

arXiv2012

Effect of lattice geometry on magnon Hall effect in ferromagnetic insulators

We have investigated the thermal Hall effect of magnons for various ferromagnetic insulators. For pyrochlore ferromagnetic insulators Lu$_2$V$_2$O$_7$, Ho$_2$V$_2$O$_7$, and In$_2$Mn$_2$O$_7$, finite thermal Hall conductivities have been observed below the Curie temperature $T_C$ . From the temperature and magnetic field dependences, it is concluded that magnons are responsible for the thermal Hall effect. The Hall effect of magnons can be well explained by the theory based on the Berry curvature in momentum space induced by the Dzyaloshinskii-Moriya (DM) interaction. The analysis has been extended to the transition metal (TM) oxides with perovskite structure. The thermal Hall signal was absent or far smaller in La$_2$NiMnO$_6$ and YTiO$_3$, which have the distorted perovskite structure with four TM ions in the unit cell. On the other hand, a finite thermal Hall response is discernible below $T_C$ in another ferromagentic perovskite oxide BiMnO$_3$, which shows orbital ordering with a larger unit cell. The presence or absence of the thermal Hall effect in insulating pyrochlore and perovskite systems reflect the geometric and topological aspect of DM-induced magnon Hall effect.

cond-mat.mtrl-sci↗

arXiv2011

Thermoelectric response in the incoherent transport region near Mott transition: the case study of La1-xSrxVO3

We report a systematic investigation on the high-temperature thermoelectric response in a typical filling-control Mott transition system La1-xSrxVO3. In the vicinity of the Mott transition, incoherent charge transport appears with increasing temperature and the thermopower undergoes two essential crossovers, asymptotically approaching the limit values expected from the entropy consideration, as known as Heikes formula. By comparison with the results of the dynamical mean field theory, we show that the thermopower in the Mott critical state mainly measures the entropy per charge carrier that depends on electronic degrees of freedom available at the measurement temperature. Our findings verify that the Heikes formula is indeed applicable to the real correlated electron systems at practical temperatures (T>200K).

cond-mat.str-el↗