arXiv subjects

K. Kamazawa

Publications and source records attributed to K. Kamazawa.

8 recordsLinked to original sources

arXiv2026

Zr-based bulk metallic glass clamp cell for high-pressure inelastic neutron scattering

We report the fabrication and characterization of a Zr-based bulk metallic glass (Zr-BMG) clamp cell designed for high-pressure inelastic neutron scattering (INS) measurements. The INS spectra of the empty cell exhibit broad and featureless backgrounds, reflecting the amorphous structure of the Zr-BMG. Test measurements using a reference sample, CsFeCl$_{3}$, confirm that the neutron transmission of the Zr-BMG cell is significantly higher than that of a conventional monobloc CuBe clamp cell. These results demonstrate that the Zr-BMG clamp cell provides both enhanced neutron transparency and a clean background profile, thereby advancing high-pressure INS studies.

cond-mat.mtrl-sci↗

arXiv2024

Understanding spin currents from magnon dispersion and polarization: Spin-Seebeck effect and neutron scattering study on Tb3Fe5O12

Magnon spin currents in the ferrimagnetic garnet Tb3Fe5O12 with 4f electrons were examined through the spin-Seebeck effect and neutron scattering measurements. The compound shows a magnetic compensation, where the spin-Seebeck signal reverses above and below Tcomp = 249.5(4) K. Unpolarized neutron scattering unveils two major magnon branches with finite energy gaps, which are well-explained in the framework of spin-wave theory. Their temperature dependencies and the direction of the precession motion of magnetic moments, i.e. magnon polarization, defined using polarized neutrons, explain the reversal at Tcomp and decay of the spin-Seebeck signals at low temperatures. We illustrate an example that momentum- and energy-resolved microscopic information is a prerequisite to understanding the magnon spin current.

cond-mat.str-el↗

arXiv2023

Observation of field-induced single-ion magnetic anisotropy in a multiorbital Kondo alloy $\mathrm{(Lu,Yb)}\mathrm{Rh}_{2}\mathrm{Zn}_{20}$

We demonstrate field-induced single-ion magnetic anisotropy resulting from the multiorbital Kondo effect on the diluted ytterbium alloy $(\mathrm{Lu}_{1-x}\mathrm{Yb}_x)\mathrm{Rh}_2\mathrm{Zn}_{20}$. Single-ion anisotropic metamagnetic behavior is revealed in low-temperature regions where the local Fermi-liquid state is formed. Specific hea, low-field magnetic susceptibility, and resistivity indicate reproduction of the ground-state properties by the $\mathrm{SU}(N = 8)$ Kondo model with a relatively large $c$-$f$ hybridization of $T_{\mathrm{K}} = 60.9 \ \mathrm{K}$. Dynamical susceptibility measurements on $\mathrm{Yb}\mathrm{Rh}_2\mathrm{Zn}_{20}$ support realizing the multiorbital Kondo ground state in $(\mathrm{Lu}_{1-x}\mathrm{Yb}_x)\mathrm{Rh}_2\mathrm{Zn}_{20}$. The single-ion magnetic anisotropy becomes evident above $\sim5 \ \mathrm{T}$, which is lower than the isotropic Kondo crossover field of 22.7 T, verifying blurred low-lying crystal field states through the multiorbital Kondo effect.

cond-mat.str-el↗

arXiv2020

Neutron powder diffraction study of NaMn$_2$O$_4$ and Li$_{0.92}$Mn$_2$O$_4$: New insights on spin-charge-orbital ordering

The high-pressure synthesized quasi-one-dimensional compounds NaMn$_2$O$_4$ and Li$_{0.92}$Mn$_2$O$_4$ are both antiferromagnetic insulators, and here their atomic and magnetic structures were investigated using neutron powder diffraction. The present crystal structural analyses of NaMn2O4 reveal that Mn3+/Mn4+ charge-ordering state exist even at low temperature (down to 1.5 K). It is evident from one of the Mn sites shows a strongly distorted Mn3+ octahedra due to the Jahn-Teller effect. Above TN = 39 K, a two-dimensional short-range correlation is observed, as indicated by an asymmetric diffuse scattering. Below TN, two antiferromagnetic transitions are observed (i) a commensurate long-range Mn3+ spin ordering below 39 K, and (ii) an incommensurate Mn4+ spin ordering below 10 K. The commensurate magnetic structure (kC = 0.5, -0.5, 0.5) follows the magnetic anisotropy of the local easy axes of Mn3+, while the incommensurate one shows a spin-density-wave order with kIC = (0,0,0.216). For Li$_{0.92}$Mn$_2$O$_4$, on the other hand, absence of a long-range spin ordered state down to 1.5 K is confirmed.

cond-mat.mtrl-sci↗

arXiv2017

Time-of-flight elastic and inelastic neutron scattering studies on the localized $4d$ electron layered perovskite La$_5$Mo$_4$O$_{16}$

The magnetic structure and spin-wave excitations in the quasi-square-lattice layered perovskite compound La$_5$Mo$_4$O$_{16}$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic stacking along the $c$ axis where the magnetic propagation vector is $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are estimated to be $0.54(2)μ_\text{B}$ for Mo$^{5+}$ ($4d^1$) ions and $1.07(3)μ_\text{B}$ for Mo$^{4+}$ ($4d^2$) ions at 4 K, which are about half of the expected values. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit interaction in Mo ions evidenced by the spin gap at the magnetic zone center. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La$_5$Mo$_4$O$_{16}$.

cond-mat.str-el↗

arXiv2014

Lithium Diffusion & Magnetism in Battery Cathode Material LixNi1/3Co1/3Mn1/3O2

We have studied low-temperature magnetic properties as well as high-temperature lithium ion diffusion in the battery cathode materials LixNi1/3Co1/3Mn1/3O2 by the use of muon spin rotation/relaxation. Our data reveal that the samples enter into a 2D spin-glass state below TSG=12 K. We further show that lithium diffusion channels become active for T>Tdiff=125 K where the Li-ion hopping-rate [nu(T)] starts to increase exponentially. Further, nu(T) is found to fit very well to an Arrhenius type equation and the activation energy for the diffusion process is extracted as Ea=100 meV.

cond-mat.mtrl-sci↗

arXiv2013

1D to 2D Na Ion Diffusion Inherently Linked to Structural Transitions in Na$_{0.7}$CoO$_{2}$

We report the observation of a stepwise "melting" of the low-temperature Na-vacancy order in the layered transition metal oxide Na0.7CoO2. High-resolution neutron powder diffraction indicates the existence of two first-order structural transitions, one at T1 = 290 K, followed by a second at T2 = 400 K. Detailed analysis reveals that both transitions are linked to changes in the Na mobility. Our data are consistent with a two-step disappearance of Na-vacancy order through the successive opening of first quasi-1D (T1 > T > T2) and then 2D (T > T2) Na diffusion paths. These results shed new light on previous, seemingly incompatible, experimental interpretations regarding the relationship between Na-vacancy order and Na dynamics in this material. They also represent an important step towards the tuning of physical properties and the design of tailored functional materials through an improved control and understanding of ionic diffusion.

cond-mat.str-el↗

arXiv2007

Frustrated minority spins in GeNi2O4

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi$_2$O$_4$ at $T_{N1}=12.1$ K and $T_{N2}=11.4$ K, respectively \cite{matsuno, crawford}. Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at $T_{N1}$ the spins on the $<111>$ \kagome planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the $<111>$ triangular planes that separate the \kagome planes frustrated and disordered. At the lower $T_{N2}$, the triangular spins also order in the $<111>$ plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.

cond-mat.str-el↗