Role of on-site Coulomb interactions in the half-metallic Weyl ferromagnet candidate thin-film CoFeSi

Sumida, Kazuki; Fujita, Yuichi*; Zhou, W.*; Masuda, Keisuke*; Kawasaki, Ikuto; Fujimori, Shinichi; Kimura, Akio*; Sakuraba, Yuya*

Physical Review B, 108(24), p.L241101_1 - L241101_6, 2023/12

https://doi.org/10.1103/PhysRevB.108.L241101

Three-dimensional bulk Fermi surfaces and Weyl crossings of CoMnGa thin films underneath a protection layer

Kono, Takashi*; Kakoki, Masaaki*; Yoshikawa, Tomoki*; Wang, X.*; Sumida, Kazuki; Muro, Takayuki*; Goto, Kazuki*; Sakuraba, Yuya*; Umetsu, Rie*; Kimura, Akio*

Physical Review B, 104(19), p.195112_1 - 195112_8, 2021/11

https://doi.org/10.1103/PhysRevB.104.195112

Angle-resolved photoelectron spectroscopy utilizing soft X-ray synchrotron radiation was applied to Heusler-type CoMnGa thin films that have a 1-nm Al capping layer. The bulk Fermi surfaces and band structures varied along the out-of-plane momentum, stemming from the three-dimensional crystal structure, in the absence of any in situ surface treatment. In addition, there were characteristic intersecting bands (Weyl cones), with crossing points near the Fermi level, which were consistent with computed results. The Weyl cones are of bulk origin and are responsible for the high anomalous Nernst and the anomalous Hall coefficients. A close comparison of the experimental band structures in CoMnGe and CoMnGa indicated that the rigid band picture is valid in both alloys and that fine carrier tuning is possible by replacing Ga with Ge to improve the anomalous conductivity.

Unveiling spin-dependent unoccupied electronic states of CoMnGe (Ga) film via Ge (Ga) absorption spectroscopy

Yoshikawa, Tomoki*; Antonov, V. N.*; Kono, Takashi*; Kakoki, Masaaki*; Sumida, Kazuki; Miyamoto, Koji*; Takeda, Yukiharu; Saito, Yuji; Goto, Kazuki*; Sakuraba, Yuya*; et al.

Physical Review B, 102(6), p.064428_1 - 064428_7, 2020/08

https://doi.org/10.1103/PhysRevB.102.064428

Spin pumping efficiency from half metallic CoMnSi

Chudo, Hiroyuki; Ando, Kazuya*; Saito, Kesami*; Okayasu, Satoru; Haruki, Rie; Sakuraba, Yuya*; Yasuoka, Hiroshi; Takanashi, Koki; Saito, Eiji

Journal of Applied Physics, 109(7), p.073915_1 - 073915_4, 2011/04

https://doi.org/10.1063/1.3556433

We present spin pumping using a Heusler alloy CoMnSi/Pt bilayer film. A spin current is produced by a ferromagnetic resonance (FMR) technique. The pure spin current injected into the Pt layer from the CoMnSi layer is detected by the inverse spin-Hall effect (ISHE), which converts the spin current into an electric current. We estimated a damping constant of the CoMnSi/Pt bilayer film from an angular dependence of FMR spectra. Using the damping constant efficiency of spin pumping from the CoMnSi layer is evaluated. We found that a mixing conductance at the CoMnSi/Pt interface is comparable to that at a permalloy/Pt interface.

Observation of spin-polarized Weyl cones and giant anomalous Nernst effect in CoMnGa films

Sumida, Kazuki; Sakuraba, Yuya*; Masuda, Keisuke*; Kono, Takashi*; Kakoki, Masaaki*; Goto, Kazuki*; Zhou, W.*; Miyamoto, Koji*; Miura, Yoshio*; Okuda, Taichi*; et al.

no journal, , 

no abstracts in English

Spin-polarized Weyl cones and giant anomalous Nernst effect in CoMnGa films

Sumida, Kazuki; Sakuraba, Yuya*; Masuda, Keisuke*; Kono, Takashi*; Kakoki, Masaaki*; Goto, Kazuki*; Zhou, W.*; Miyamoto, Koji*; Miura, Yoshio*; Okuda, Taichi*; et al.

no journal, , 

no abstracts in English

Temperature-dependent spin-polarized electronic structure of the half-metallic Heusler alloy CoMnSi films

Sumida, Kazuki; Kakoki, Masaaki*; Sakuraba, Yuya*; Masuda, Keisuke*; Kono, Takashi*; Goto, Kazuki*; Miyamoto, Koji*; Miura, Yoshio*; Hono, Kazuhiro*; Okuda, Taichi*; et al.

no journal, , 

Positron annihilation spectroscopy as a probe for spintronics; Hope to the first principles calculation

Kawasuso, Atsuo; Maekawa, Masaki; Fukaya, Yuki; Sakuraba, Yuya*; Saito, Eiji; Takanashi, Koki*

no journal, , 

Spin-polarized positron annihilation spectroscopy can be used for the studies of ferromagnetic electron momentum distribution and topmost surface electron spins. From this viewpoint, we argue the possibility of spin-polarized positron annihilation spectroscopy as a probe for spintronics materials. In the presentation, we introduce the theoretical formulation of the spin-polarized positron annihilation spectroscopy with some examples on classical ferromagnets, the latest results on the current-induced spin polarization, and some hopes to the first principles calculation to assist experiments.

Spin pumping in CoMnSi

Chudo, Hiroyuki; Ando, Kazuya*; Saito, Kesami*; Okayasu, Satoru; Haruki, Rie; Sakuraba, Yuya*; Yasuoka, Hiroshi; Takanashi, Koki; Saito, Eiji

no journal, , 

no abstracts in English

An Attempt to measure spin-polarization of Heusler alloy CoMnSi using spin-polarized positron annihilation

Kawasuso, Atsuo; Sakuraba, Yuya*; Fukaya, Yuki; Zhang, H.; Maekawa, Masaki; Mochizuki, Izumi; Takanashi, Koki*

no journal, , 

We are attempting to determine the spin-polarization of the Heusler alloys using spin-polarized positron annihilation spectroscopy. Positrons implanted near the surface combine with electrons to form positronium (Ps). From the o-Ps (spin triplet state) fraction, one can determine the electron spin-polarization. The samples used in this study are CoMnSi films grown on MgO(001) substrates. To avoid the surface oxidation, the sample surfaces are capped with Au thin layers (0.5 nm thick). The electron polarization are obtained to be 0.26. This is significantly smaller than that determined by using the Andreev reflection method. The further study using samples without any cap layers are needed.