arXiv subjects

Rikako Yamamoto

Publications and source records attributed to Rikako Yamamoto.

5 recordsLinked to original sources

arXiv2026

Static and Dynamic Electronic Properties and the Possible Magnetic Structure of the $4f^3$-$Γ_6$ System NdCo2Zn$_{18}$Ga$_2$ Investigated Using $^{59}$Co Nuclear Quadrupole Resonance

We report $^{59}$Co nuclear quadrupole resonance (NQR) measurements on the Nd-based compound NdCo$_2$Zn$_{18}$Ga$_2$, which undergoes an antiferromagnetic transition at $T_{\rm N} = 1.5$ K. Although the NQR spectra show no detectable change across $T_{\rm N}$, the nuclear spin-lattice relaxation rate, $1/T_1$, exhibits a clear anomaly at $T_{\rm N}$. An analysis based on the alignment of the Nd moments demonstrates that the internal magnetic fields generated by these moments cancel each other at the Co sites. If the nearest-neighbor Nd moments align antiferromagnetically, this finding suggests that Ga substitution removes magnetic frustration, thereby increasing $T_{\rm N}$.

cond-mat.str-el↗

arXiv2025

Interlinking helical spin textures in nanopatterned chiral magnets

Nanoscale topologically non-trivial magnetization configurations generate significant interest due to both the fundamental properties of their knotted structures and their potential applications in ultra-efficient computing devices. While such textures have been widely studied in two dimensions, three-dimensional (3D) systems can yield more complex configurations, resulting in richer topologies and dynamic behaviors. However, reliably nucleating these 3D textures has proven challenging, and so far, 3D configurations such as vortex rings and hopfions can often only be observed forming spontaneously in relatively uncontrolled manners. Here, we demonstrate that through the 3D nanopatterning of chiral single crystal helimagnets into nano-tori, the controlled formation of a magnetic double helix can be achieved. This surface-localized topological state is stabilized by the interplay of intrinsic exchange interactions of the single crystal with the extrinsic emergent effects of the patterned geometry. These double helices host magnetic defects akin to supercoiling in circular DNA and climbing vines. We expect this study to serve as a foundation for future research combining single crystal systems with 3D nanopatterning, offering a new degree of control over emergent phenomena in nanoscale magnets and wider quantum material systems.

cond-mat.mes-hall↗

arXiv2025

Altermagnetic nanotextures revealed in bulk MnTe

With many candidate altermagnetic materials, MnTe has emerged as one of the most promising systems, with growing experimental evidence for altermagnetic phenomena. So far, the majority of measurements have been performed on thin-films, or have involved surface measurements. However, the question of altermagnetic order in the bulk system - in the absence of substrate or surface effects - remains. Here we show evidence for bulk altermagnetism in single crystal MnTe, through spectroscopic X-ray microscopy. By performing nanoscale X-ray magnetic circular dichroic (XMCD) imaging in transmission on a 200 nm thick lamella, we observe domains and magnetic textures with a spectroscopic signature characteristic of altermagnetic order, thereby confirming the intrinsic nature of altermagnetism in MnTe. Quantitative analysis of the XMCD signal reveals an excellent agreement with predicted signals, establishing that the altermagnetic order exists throughout the thickness of the lamella and confirming the intrinsic, bulk nature of the state. With these results, we demonstrate that transmission XMCD spectroscopic imaging is a robust, quantitative technique to probe altermagnetic order, providing a means to probe individual altermagnetic domains within complex configurations. This ability to investigate, and characterise altermagnetic order in bulk crystals represents an important tool for the exploration of altermagnetism across a wide range of candidate materials, of key importance for the development of future technologies.

cond-mat.mtrl-sci↗

arXiv2025

Observation of spin splitting in the surface electronic structure of antiferromagnet NdBi

Spin splitting in electronic band structures via antiferromagnetic orders is a new route to control spin-polarized carriers that is available for spintronics applications. Here, we investigated the spin degree of freedom in the electronic band structures of the antiferromagnet NdBi using laser-based spin- and angle-resolved photoemission spectroscopy (laser-SARPES). Our laser-SARPES experiments revealed that the two surface bands that appear in the antiferromagnetic state are spin-polarized in opposite directions as a counterpart of the spin splitting. Moreover, we observed that the spin polarization is antisymmetric to the electron momentum, indicating that spin degeneracy is lifted due the breaking of inversion symmetry at the surface. These results are well reproduced by our density functional theory calculations with the single-q magnetic structure, implying that the spin-split surface state is determined by the breaking of inversion symmetry in concert with the antiferromagnetic order.

cond-mat.mtrl-sci↗

arXiv2023

Inelastic neutron scattering study of crystalline electric field excitations in the caged compounds NdT2Zn20 (T = Co, Rh, and Ir)

We have measured crystalline electric field (CEF) excitations of Nd3+ ions in the two-channel Kondo lattice candidates NdT2Zn20 (T = Co, Rh, and Ir) by means of inelastic neutron scattering (INS). In the INS measurements at 5 K, dispersionless excitations were observed at 3.8 and 7.2 meV for T = Co, 3.1 and 5.8 meV for T = Rh, and 3.0 and 5.3 meV for T = Ir. Analyses of the temperature dependence of the INS spectra confirm that the CEF ground states are the Gamma 6 doublet, that is a requisite for manifestation of the magnetic two-channel Kondo effect. For T = Co, a shoulder was observed at 7.7 meV close to the CEF excitation peak centered at 7.2 meV. The shoulder is attributed to a bound state of the CEF and low-lying optical phonon excitations.

cond-mat.str-el↗