Yutaka Ikedo

Li diffusion in LixCoO2 probed by muon-spin spectroscopy.

The diffusion coefficient of Li+ ions (D(Li)) in the battery material LixCoO2 has been investigated by muon-spin relaxation (mu+SR). Based on experiments in zero and weak longitudinal fields at temperatures up to 400 K, we determined the fluctuation rate (nu) of the fields on the muons due to their interaction with the nuclear moments. Combined with susceptibility data and electrostatic potential calculations, clear Li+ ion diffusion was detected above approximately 150 K. The D(Li) estimated from nu was in very good agreement with predictions from first-principles calculations, and we present the mu+SR technique as an optimal probe to detect D(Li) for materials containing magnetic ions.

Static magnetic order in metallic K0.49CoO2.

By means of muon-spin spectroscopy, we have found that K0.49CoO2 crystals undergo successive magnetic transitions from a high-T paramagnetic state to a magnetic ordered state below 60 K and then to a second ordered state below 16 K, even though K0.49CoO2 is metallic at least down to 4 K. An isotropic magnetic behavior and wide internal-field distributions suggest the formation of a commensurate helical spin density wave (SDW) state below 16 K, while a linear SDW state is likely to exist above 16 K. It was also found that exhibits a further transition at 150 K presumably due to a change in the spin state of the Co ions. Since the dependence of the internal-field below 60 K was similar to that for Na0.5CoO2, this suggests that magnetic order is more strongly affected by the Co valence than by the interlayer distance or interaction and/or the charge ordering.

The magnetic structure of the zigzag chain family Na

We present muon-spin-rotation measurements on polycrystalline samples of the complete family of the antiferromagnetic AF zigzag chain compounds, NaxCa1�xV2O4. In this family, we explore the magnetic properties from the metallic NaV2O4 to the insulating CaV2O4. We find a critical xc0.833 which separates the low and high Na-concentration-dependent transition temperature and its magnetic ground state. In the xxc compounds, the magnetic ordered phase is characterized by a single homogenous phase and the formation of incommensurate spin-density-wave order. Whereas in the xxc compounds, multiple subphases appear with temperature and x. Based on the muon data obtained in zero external magnetic field, a careful dipolar field simulation was able to reproduce the muon behavior and indicates a modulated helical incommensurate spin structure of the metallic AF phase. The incommensurate modulation period obtained by the simulation agrees with that determined by neutron diffraction.

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The magnetic nature of the CaFe 2 O 4 -type NaMn 2 O 4 and Li 0.92 Mn 2 O 4 , in which Mn ions form a zigzag chain along the b -axis, have been investigated by muon-spin rotation and relaxation (µ + SR) and susceptibility (χ) measurements in the temperature range between 1.9 and 250 K using polycrystalline samples. Weak transverse-field µ + SR measurements revealed the existence of a bulk antiferromagnetic (AF) transition for NaMn 2 O 4 at T N =39 K and for Li 0.92 Mn 2 O 4 at T N =44 K, although the χ( T ) curve did not exhibit a clear anomaly around T N for either compound. Below T N , however, the zero-field µ + SR spectra in both samples did not show the oscillatory signal characteristic of long range magnetic order. Instead, a slowly relaxing tail is observed. Comparisons with the calculated internal magnetic field for the AF ordered phase suggests that the AF spin structure is disordered and/or rapidly fluctuating. In the paramagnetic region above 100 K, a nuclear magnetic field in Li 0.92 Mn 2 O 4 ...

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Shunsuke MAKIMURA*1, 2, Naritoshi KAWAMURA1, 2, Satoshi ONIZAWA3, Yukihiro MATSUZAWA3, Masato TABE4, Yasuo KOBAYASHI1, 2, Ryo SHIMIZU3, Hiroshi FUJIMORI1, 2, Yutaka IKEDO1, 2, Ryosuke KADONO1, 2, Akihiro KODA1, 2, Kenji M. KOJIMA1, 2, Kusuo NISHIYAMA1, 2, Jumpei NAKAMURA1, 2, Koichiro SHIMOMURA1, 2, Patrick STRASSER1, 2, Masaharu AOKI5, Yohei NAKATSUGAWA2, and Yasuhiro MIYAKE1, 2 . 1Muon Section, Materials and Life Science Division, J-PARC center, Tokai, Ibaraki 319-1195, Japan 2Muon Science Laboratory, High Energy Accelerator Research Organization (KEK-IMSS), Tokai, Ibaraki 319-1195, Japan 3The NIPPON ADVANCED TECHNOLOGY CO., LTD (NAT), Tokai, Ibaraki 319-1112, Japan 4Seekel Co., Ltd., Mito, Ibaraki 310-0851, Japan 5Osaka University, Toyonaka, Osaka 560-0043, Japan

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Yutaka Ikedo1,2, Yasuhiro Miyake1,2, Koichiro Shimomura1,2, Patrick Strasser1,2, Naritoshi Kawamura1,2, Kusuo Nishiyama1,2, Shunsuke Makimura1,2, Hiroshi Fujimori1,2, Akihiro Koda1,2, Jumpei Nakamura1,2, Takashi Nagatomo1,2, Yasuo Kobayashi1,2, Taihei Adachi3, Amba Datt Pant4, Toru Ogitsu5,2, Tatsushi Nakamoto5,2, Kenichi Sasaki5,2, Hirokatsu Ohhata5,2, Ryutaro Okada5,2, Akira Yamamoto5, Yasuhiro Makida6,2, Makoto Yoshida6,2, Takahiro Okamura6,2, Ryuji Ohkubo7, Wataru Higemoto8,2, Takashi U. Ito8,2, Kazutaka Nakahara9, Kazuhiko Ishida10 1Muon Science Laboratory, Institute of Material and Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 2J-PARC Center, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan 3Faculty of Science, University of Tokyo, 7-3-1 hongo, Bunkyo, Tokyo 113-0501, Japan 4Interdiscplinary Graduate School of Medicine and Engineering, Yamanashi University, 4-3-11 Takeda, Kofu, Yamanashi 400–8511, Japan 5Cryogenics Science Center, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 6Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 7Mechanical Engineering center, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 8Advance Science Research Center, Japan Atomic Energy Agency, 2-4 shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan 9Department of Physics, University of Maryland, College Park, MD 20742 4111, USA 10Advanced Meson Science Laboratory, Nishina Center, RIKEN, 2-1 hirosawa, Wako, Saitama 351-0198, Japan

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A superconducting magnet system, which is composed of an 8 m long solenoid for transportation and 12 short solenoids for focusing, has been developed for Muon Science Establishment facility of J-PARC. The transport solenoid is composed of a 6 m straight section connected to a 45 degree curved section at each end. Muons of various momenta and of both electric charges are transported through the solenoid inner bore with an effective diameter of 0.3 m, where 2 T magnetic field is induced. There are 12 focusing solenoids with an effective bore diameter of 0.6 m and a length of 0.35 m arranged on a straight line at suitable intervals. The maximum central field of each focusing solenoid is 0.66 T. All solenoid coils are cooled by GM cryocoolers through their own conductions. The magnet system has been installed into the beam line in the summer of 2012, and its performance has been checked. Beam commissioning has been carried out since October 2012. During beam operation, temperature rise over 6 K in the transport solenoid due to a nuclear heating from the muon production target is observed at beam intensity of about 300 kW.

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In order to study a change in electrochemical, structural, and magnetic properties for lithium manganese oxide spinels Li[LixMn2−x]O4 (LMO) with 0 ≤ x ≤ 1/3, muon-spin rotation and relaxation (μSR) spectra were recorded under pressure (P) up to 2.1 GPa. At ambient P, P = 0.1 MPa, the antiferromagnetic or spin-glass-like transition temperature (Tm) at P = 0.1 MPa monotonically decreases with increasing x. On the contrary, the slope of the Tm vs. P (dTm/dP) rapidly increases from 0.9(1) K/GPa at x = 0 to 1.4 K/GPa at x = 0.1, then drops to 0.7(1) K/GPa at x = 0.15, and finally keeps constant (∼0.4 K/GPa) with further increasing x. Considering the structural change of LMO with x, the decrease in the distance between Mn ions (dMn-Mn) is likely to play an essential role for determining Tm under P. According to cyclic voltammetry on LMO, the peak current at both anodic and cathodic directions shows the maximum at x = 0.1, indicating the highest diffusivity of Li+ ions (DLi) at x = 0.1.

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1 Muon Science Laboratory, KEK, Tsukuba, Ibaraki 305-0801, Japan 2 Muon section, Materials and Life Science division, J-PARC Center, Tokai, Ibaraki 319-1195, Japan Nishina Center, RIKEN, Wako, Saitama 351-0198, Japan Advanced Science Research Center, JAEA, Tokai, Ibaraki 319-1195, Japan 5 Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Kofu, Yamanashi 400-8511, Japan # a corresponding author: E-mail adachit@post.kek.jp

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The ultra-slow muon beam is expected to be a new probe for surface and interface physics. A new beamline for the ultra-slow muon is now under construction at the J-PARC. Before transporting ultra-slow muons through the transport system, we tuned the system utilizing laser ionized hydrogen ions as ultra-slow beam. We successfully transported ions to the end of the beam line. Optimization of the beam transport system is in progress to be ready for generating the ultra-slow muon beam.