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Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ueda, Hiroaki*; Tanioku, Yasuaki*; Michioka, Chishiro*; Yoshimura, Kazuyoshi*; Takao, Kenta*; Shimoda, Aiko*; et al.
Physical Review B, 98(6), p.064403_1 - 064403_10, 2018/08
Times Cited Count:10 Percentile:46.45(Materials Science, Multidisciplinary)To specify preferential occupation sites of Co substituents and to clarify charge and spin states of Co ions in (La, Co)-cosubstituted hexagonal magnetoplumbite-type (M-type) Sr ferrite, Fe and Co nuclear magnetic resonance (NMR) spectra are measured under zero and external magnetic fields using powdered and single crystalline specimens. To a considerable degree, the charge compensation between La and Co works in the equal (La, Co)-codoped case, where more than half of the Co ions are considered to be present in the minority spin sites at the center of the oxygen tetrahedra, with the = 3/2 state carrying a small orbital moment owing to spin-orbit interaction. The remaining small number of high-spin Co ( = 3/2, = 1) ions with unquenched orbital moments would be distributed to the other octahedral , , and sites.
Imai, Masaki; Michioka, Chishiro*; Ueda, Hiroaki*; Yoshimura, Kazuyoshi*
Physical Review B, 95(5), p.054417_1 - 054414_7, 2017/02
Times Cited Count:2 Percentile:11.64(Materials Science, Multidisciplinary)We took P NMR measurements of mainly paramagnetic phase to reveal the itinerant-electron metamagnetic transition, and of its magnetically ordered phase, and characterized their spin fluctuations by estimating the spin fluctuation parameter corresponding to the width of the spin fluctuation in the spectrum in frequency space. As increases from 0 to 0.5, the in-plane component of decreases proportionally with the metamagnetic transition field. In the antiferromagnetic cT phase, is constant and spin fluctuations show an isotropic character in contrast to their behavior in the paramagnetic ucT phase. These results indicate that the in-plane spin fluctuations due to the quasi-two-dimensional crystal structure play a significant role in the metamagnetic transition of this system.
Koyama, Takehide*; Ozaki, Yuzuru*; Ueda, Koichi*; Mito, Takeshi*; Kohara, Takao*; Waki, Takeshi*; Tabata, Yoshikazu*; Michioka, Chishiro*; Yoshimura, Kazuyoshi*; Suzuki, Michito; et al.
Journal of the Physical Society of Japan, 81(Suppl.B), p.SB008_1 - SB008_5, 2012/12
Times Cited Count:1 Percentile:10.83(Physics, Multidisciplinary)The normal state properties of a noncentrosymmetric superconductor MoAlC are studied by means of the nuclear magnetic resonance (NMR) experiment. The change of NMR line shape and the peak of the nuclear spin-echo decay rate at 130 K indicate that the MoAlC exhibits the phase transition prior to the emergence of superconductivity. The reduction in the conduction electron density is inferred from the decrease in the nuclear spin-lattice relaxation rate. The nature of the newly found phase transition is discussed by considering the result of the first principle calculations, indicating a good nesting property of the Fermi surfaces.
Koyama, Takehide*; Ozaki, Yuzuru*; Ueda, Koichi*; Mito, Takeshi*; Kohara, Takao*; Waki, Tsuyoshi*; Tabata, Yoshikazu*; Michioka, Chishiro*; Yoshimura, Kazuyoshi*; Suzuki, Michito; et al.
Physical Review B, 84(21), p.212501_1 - 212501_4, 2011/12
Times Cited Count:11 Percentile:44.74(Materials Science, Multidisciplinary)The results of Al nuclear magnetic resonance and specific-heat measurements of the noncentrosymmetric superconductor MoAlC are reported. The phase transition around 130 K is inferred from a distinct change in the NMR spectrum, a clear peak in the spin-echo decay rate, and an anomaly in the specific heat. Possibility of charge-density wave ordering around 130 K is discussed by calculating the Fermi surfaces in the normal states and considering the partial quenching of the Fermi surfaces with the decrease in 1/ below the superconducting transition temperature.