M. Matsumura

Muon sites in Ce(Ru,Rh)2Al10 investigated by using Density Functional Theory from the view point of electronic potential

Numerical investigations on muon sites in Ce-based Kondo semiconductors, Ce(Ru,Rh)2Al10 were carried out by using the Density Functional Theory. From the view point of simple electrostatic potential calculations, we found all the previously reported muon sites, suggested by different groups (Kambe S et al. 2010 J. Phys. Soc. Jpn. 79 053708 and Khalyavin D D et al., 2010 Phys. Rev. B 82 100405(R)), can be possibly chosen as muon stopping sites. We also investigated the changes in the potential of the Rh-doped case. We discovered that the electronic potential around the nearest Ru atom to the substituted Rh atom is affected and the potential becomes asymmetric around the nearest Ru ion. Although big changes in hyperfine fields at muon sites have been reported (Guo H et al. 2013 Phys. Rev. B 88 115206), the muon positions estimated from the potential calculations do not change much.

Temperature oscillation suppression of GM cryocooler

GM cryocooler is a convenient refrigerator to achieve low temperatures about 4 K, while it is not suitable for precise measurements because of the large temperature oscillation of typically about 0.3 K. To resolve this problem, we have developed an adapter (He-pot) with a simple structure as possible. From the thermodynamic consideration, both heat capacity and thermal conductance should be large in order to reduce the temperature oscillation without compromising cooling power. Optimal structure of the He-pot is a copper cylinder filled with high pressure He-gas at room temperature. This can reduce the temperature oscillation to less than 10 mK below a certain temperature TH without compromising cooling power. TH are 3.8 and 4.5 for filled He-gas pressures of 90 and 60 atm, respectively. By using this He-pot, GM cryocooler can be applied to such as precise physical property measurements and THz detection.

Secondary magnetic transition in tetragonal YBa2Cu3Ox with 6.1 ≤ x ≤ 6.4

In the antiferromagnetic state of YBa 2 Cu 3 O x with 6.1≤ ≤ 6.4, the effective nuclear spin relaxation rates, T 2 * − and T 2 * − , of Cu(l) site are enhanced remarkably at 20 and 35–40 K, respectively, suggesting the secondary magnetic transition sufficiently below the Neel temperature. Some discussions are made on this secondary transition .

Single crystal growth and low temperature magnetic properties of the Ce-Cu-Al ternary system

We have succeeded in growing BaAl4-type CeCuxAl4−x (x ~ 0.7) and ThMn12-type CeCu4Al8 by Al self-flux method for the first time, and the magnetic susceptibility χ and electrical resistivity ρ have been measured. These measurements indicate that CeCuxAl4−x is a ferromagnet with the Curie temperature of 3.7 K, and another unknown phase transition appears at T0 = 6.8 K as an abrupt increase in ρ. This latter transition is probably not due to magnetic origin, because χ does not show any anomalies at around T0. CeCu4Al8 orders antiferromagnetically below 4.7 K. We have performed crystalline electric field analysis from the anisotropy in χ, and clarified that Kondo effect plays an important role especially for CeCu4Al8.

Temperature dependence of 55Mn and 51V NMR frequencies on various environments in Fe and Ni

Abstract The hyperfine field of the satellite line for 55 Mn decreases more rapidly than that of the main line with increasing temperature in Fe Mn and Ni Mn alloys. However, it is not so for 51 V in a Fe V alloy. Some discussions are made on this “local environment” effect.

Co-NQR Study on Successive Magnetic Phase under Pressure in Non-centrosymmetric CeCoGe3

We have performed Co-NQR study to clarify the complex magnetic phases in approaching to the quantum critical point (QCP). The successive transitions at TN2=12 K and TN3=8 K after the ferrimagnetic-like order at TN1=21 K in ambient pressure are confirmed by the spectral changes of Co-NQR However no critical slowing down of the nuclear spin-lattice relaxation rate 1/T1 or the nuclear spin-spin relaxation rate 1/T2 at TN2 and TN3 was observed, suggesting 1st order transitions. In applying pressure, a large spectral change of Co-NQR occurs in relatively low pressure of 0.3 Gpa. The Co-NQR spectrum becomes simple above about 0.7 GPa, consisting of the two Co sites with spectral weight ratio of 2. No successive transitions were observed in 1.5 GPa, indicating that the successive transitions are confined to relatively low pressure region. The extremely slower decrease of the sublattice magnetization than that expected in the mean field approximation is seen in 1.5 GPa.

Raman scattering spectra of LaRu2Al10 and CeRu2Al10

Phonon spectra of LaRu2Al10 and CeRu2Al10 have been studied by Raman scattering from 3.4K to 300K. Polarization dependence at room temperature gives the precise mode assignment for the sake of first principles calculation results. The measured Raman spectra are well explained by the space group Cmcm and there is no remarkable difference between LaRu2Al10 and CeRu2Al10. Since we observed no anomaly at T0 = 27K in CeRu2Al10, the lattice distortion due to the structural transition has not been detected. From the temperature dependence of the vibrational frequency of Ce and La, their vibrational amplitude is not large in CeRu2Al10 and LaRu2Al10, that is, close to harmonic case.

Dilution effect of Ce ion in CeRu2Al10

CeRu2Al10 causes a mysterious phase transition at T0~27 K In order to examine the feature of this transition, we have measured the magnetic susceptibility and electrical resistivity of Ce1-xRxRu2Al10 (R=La, La0.63Y0.37, Y) system in which Ce ions in CeRu2Al10 are replaced by non-magnetic rare earth ions with different ionic radii, where the relationship among the ionic radii is La3+ > (***La0.63Y0.37)3+ ~ Ce3+ > Y3+.*** The magnitude of the magnetic susceptibility becomes smaller with decreasing ionic radii, indicating Kondo temperature increases due to the chemical pressure effect. In the La- and La0.63Y0.37-substituted system, T0 decreases monotonically and disappears smoothly at x~0.7, while in the Y-substituted system, T0 decreases more slowly and disappears suddenly between x=0.4 and 0.5. These behaviors cannot be understood by a simple magnetic phase transition, suggesting that the change in valence of Ce ion plays an important role in the mysterious phase transition.

Magnetic properties of R3Al11(R=La, Ce, Pr, Nd, Sm) single crystals

R3Al11(R=La, Ce, Pr, Nd, Sm) crystallizes in the orthorhombic La3Al11-type structure with two inequivalent R sites. We have succeeded in growing these single crystals by using Al self flux method, and have performed the magnetization. All of the compounds except for nonmagnetic La3Al11 show successive phase transition and R3Al11(R=Ce, Pr, Nd) exhibits metamagnetism at low temperature. As reported previously, Ce3Al11 shows a ferromagnetic transition at 6.2 K and an antiferromagnetic one at 3.2 K for the b axis and, in addition, we have found another anomalies inferred to be antiferromagnetic transition. Pr3Al11 shows an antiferromagnetic transition at 12.7 K and a ferromagnetic one at 3.5 K. Nd3Al11 shows three antiferromagnetic transitions at 13.5 K, 9.5 K and 2.9 K. Sm3Al11 does not follow the Curie-Weiss low and shows two antiferromagnetic transitions at 50 K and 26 K. These complex phase transitions and metamagnetism can be explained by two inequivalent R ions with different crystal symmetry.

27Al-NQR Study on Novel Phase Transition in CeOs2Al10

We have performed 27Al-NQR measurements in CeOs2Al10 which exhibits a novel phase transition at T0=29 K The NQR parameters determined for all the Al sites in ambient pressure were compared with those in CeRu2Al10 with T0=27 K and CeFe2Al10 with no phase transition. The distinct NQR splitting just below T0=32.5 K under pressure 0.66 GPa ensures an enhancement of T0 and a homogeneous transition. Despite the increase of T0, the nuclear spin-lattice relaxation rate 1/Tl is suppressed over whole range of temperature than in ambient pressure. The characteristic features of no critical slowing down at T0 and of the remarkable decrease of 1/T1T starting at T > T0 become prominent under pressure, suggesting an approach to Kondo semiconductor in a valence fluctuation regime.