SR studies on copper minerals

Fujihara, Masayoshi; Okabe, Hirotaka*; Koda, Akihiro*

Interactions (Internet), 245(1), p.13_1 - 13_6, 2024/12

https://doi.org/10.1007/s10751-024-01856-7

Quantum states are difficult to observe experimentally. In addition, ideal model materials have not been found for some of the lattice systems in which exotic quantum states are predicted to be realized. Numerous candidates for low-dimensional quantum magnets are hidden in copper minerals, and the number of candidates is increasing every year. We succeeded to synthesize seven copper minerals by imitating the environment where they are discovered and reported their quantum states. The properties of pulsed muons are very suitable for investigating the spin state of artificial copper minerals.

Magnetic hysteresis induction with nanocolumnar defects in magnetic insulators

Harii, Kazuya*; Umeda, Maki; Arisawa, Hiroki*; Hioki, Tomosato*; Sato, Nana; Okayasu, Satoru; Ieda, Junichi

Journal of the Physical Society of Japan, 92(7), p.073701_1 - 073701_4, 2023/07

https://doi.org/10.7566/JPSJ.92.073701

Gyromagnetic bifurcation in a levitated ferromagnetic particle

Sato, Tetsuya*; Kato, Takeo*; Oue, Daigo*; Matsuo, Mamoru

Physical Review B, 107(8), p.L180406_1 - L180406_6, 2023/05

https://doi.org/10.1103/PhysRevB.107.L180406

Thermal stability of non-collinear antiferromagnetic MnSn nanodot

Sato, Yuma*; Takeuchi, Yutaro*; Yamane, Yuta*; Yoon, J.-Y.*; Kanai, Shun*; Ieda, Junichi; Ohno, Hideo*; Fukami, Shunsuke*

Applied Physics Letters, 122(12), p.122404_1 - 122404_5, 2023/03

https://doi.org/10.1063/5.0135709

Magnonic Casimir effect in ferrimagnets

Nakata, Koki; Suzuki, Kei

Physical Review Letters, 130(9), p.096702_1 - 096702_6, 2023/03

https://doi.org/10.1103/PhysRevLett.130.096702

Quantum fluctuations of quantum fields induce a zero-point energy shift under spatial boundary conditions. This quantum phenomenon, called the Casimir effect, has been attracting much attention beyond the hierarchy of energy scales, whereas its application to spintronics has not yet been investigated enough, particularly to ferrimagnetic thin films. Here we fill this gap. Using the lattice field theory, we investigate the Casimir effect induced by quantum fields for magnons and find that the magnonic Casimir effect can arise not only in antiferromagnets but also in ferrimagnets (e.g., YIG). Thus, we pave the way for magnonic Casimir engineering.

Local bifurcation with spin-transfer torque in superparamagnetic tunnel junctions

Funatsu, Takuya*; Kanai, Shun*; Ieda, Junichi; Fukami, Shunsuke*; Ohno, Hideo*

Nature Communications (Internet), 13, p.4079_1 - 4079_8, 2022/07

https://doi.org/10.1038/s41467-022-31788-1

Modulation of the energy landscape by external perturbations governs various thermally-activated phenomena, described by the Arrhenius law. Thermal fluctuation of nanoscale magnetic tunnel junctions with spin-transfer torque (STT) shows promise for unconventional computing, whereas its rigorous representation, based on the Neel-Arrhenius law, has been controversial. In particular, the exponents for thermally-activated switching rate therein, have been inaccessible with conventional thermally-stable nanomagnets with decade-long retention time. Here we approach the Neel-Arrhenius law with STT utilising superparamagnetic tunnel junctions that have high sensitivity to external perturbations and determine the exponents through several independent measurements including homodyne-detected ferromagnetic resonance, nanosecond STT switching, and random telegraph noise. Furthermore, we show that the results are comprehensively described by a concept of local bifurcation observed in various physical systems. The findings demonstrate the capability of superparamagnetic tunnel junction as a useful tester for statistical physics as well as sophisticated engineering of probabilistic computing hardware with a rigorous mathematical foundation.

Large antisymmetric interlayer exchange coupling enabling perpendicular magnetization switching by an in-plane magnetic field

Masuda, Hiroto*; Seki, Takeshi*; Yamane, Yuta*; Modak, R.*; Uchida, Kenichi*; Ieda, Junichi; Lau, Y.-C.*; Fukami, Shunsuke*; Takanashi, Koki

Physical Review Applied (Internet), 17(5), p.054036_1 - 054036_9, 2022/05

https://doi.org/10.1103/PhysRevApplied.17.054036

The antisymmetric interlayer exchange coupling (AIEC) was recently discovered, playing pivotal roles in magnetization switching of a synthetic antiferromagnet (SAF) through inducing magnetization canting. Large AIEC is reported for perpendicularly magnetized Pt/Co/Ir/Co/Pt with wedge-shaped layers. The effective field of the AIEC is related with symmetric interlayer exchange coupling, providing guides to enhance the AIEC. We develop an extended Stoner-Wohlfarth model for a SAF, revealing key factors in its magnetization switching. Combining the theoretical knowledge and the experimental results, perpendicular magnetization switching is achieved solely by an in-plane magnetic field.

Observation of domain structure in non-collinear antiferromagnetic MnSn thin films by magneto-optical Kerr effect

Uchimura, Tomohiro*; Yoon, J.-Y.*; Sato, Yuma*; Takeuchi, Yutaro*; Kanai, Shun*; Takechi, Ryota*; Kishi, Keisuke*; Yamane, Yuta*; DuttaGupta, S.*; Ieda, Junichi; et al.

Applied Physics Letters, 120(17), p.172405_1 - 172405_5, 2022/04

https://doi.org/10.1063/5.0089355

Slow electronic dynamics in the paramagnetic state of UTe

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Haga, Yoshinori; Tokiwa, Yoshifumi; Opletal, P.; Fujibayashi, Hiroki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; et al.

Journal of the Physical Society of Japan, 91(2), p.023707_1 - 023707_5, 2022/02

https://doi.org/10.7566/JPSJ.91.023707

Te NMR experiments in field () applied along the easy magnetization axis (the -axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 3040 K, where the spin susceptibility along the hard magnetization axis (the -axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in . We suggest that UTe would be located on the paramagnetic side near an electronic phase boundary, where either the magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.

Unveiling unconventional magnetism at the surface of SrRuO

Fittipaldi, R.*; Hartmann, R.*; Mercaldo, M. T.*; Komori, Sachio*; Bjrlig, A.*; Higemoto, Wataru; Maeno, Yoshiteru*; Di Bernardo, A.*; 18 of others*

Nature Communications (Internet), 12, p.5792_1 - 5792_9, 2021/10

https://doi.org/10.1038/s41467-021-26020-5

The layered oxide perovskite SrRuO, which has been intensively investigated due to its unusual properties. Whilst the debate on the symmetry of the superconducting state in SrRuO is still ongoing, a deeper understanding of the SrRuO normal state appears crucial as this is the background in which electron pairing occurs. Here, by using low-energy muon spin spectroscopy we discover the existence of surface magnetism in SrRuO at an onset temperature higher than 50 K. Our observations set a reference for the discovery of the same magnetic phase in other materials.