Microscopic Magnetic Properties of (V1−x_{1-x}Tix_{x})2_2O3_3 near the Phase Boundary of the Metal-Insulator Transition

Magnetic susceptibility (chi) and $^{51}$V NMR have been measured in (V$_{1-x}$Ti$_{x}$)$_2$O$_3$ near the phase boundary of the metal-insulator transition. It is established that the transition from antiferromagnetic insulating (AFI) to antiferromagnetic metallic phases near $x_{\rm c}\approx 0.05$ is not quantum critical but is discontinuous with a jump of the transition temperature. In the AFI phase at 4.2 K, we observed the satellite in the zero-field $^{51}$V NMR spectrum around 181 MHz in addition to the ``host'' resonance around 203 MHz. The satellite is also observable in the paramagnetic metallic phase of the x = 0.055 sample. We associated the satellite with the V sites near Ti which are in the V$^{3+}$-like oxidation state but has different temperature dependence of the NMR shift from that of the host V site. The host d-spin susceptibility for x = 0.055 decreases below $\sim$60 K but remains finite in the low-temperature limit.Comment: 9 pages, 4 eps figures; corrected the author lis

Coexistence of double alternating antiferromagnetic chains in (VO)_2P_2O_7 : NMR study

Nuclear magnetic resonance (NMR) of 31P and 51V nuclei has been measured in a spin-1/2 alternating-chain compound (VO)_2P_2O_7. By analyzing the temperature variation of the 31P NMR spectra, we have found that (VO)_2P_2O_7 has two independent spin components with different spin-gap energies. The spin gaps are determined from the temperature dependence of the shifts at 31P and 51V sites to be 35 K and 68 K, which are in excellent agreement with those observed in the recent inelastic neutron scattering experiments [A.W. Garrett et al., Phys. Rev. Lett. 79, 745 (1997)]. This suggests that (VO)_2P_2O_7 is composed of two magnetic subsystems showing distinct magnetic excitations, which are associated with the two crystallographically-inequivalent V chains running along the b axis. The difference of the spin-gap energies between the chains is attributed to the small differences in the V-V distances, which may result in the different exchange alternation in each magnetic chain. The exchange interactions in each alternating chain are estimated and are discussed based on the empirical relation between the exchange interaction and the interatomic distance.Comment: 10 pages, 11 embedded eps figures, REVTeX, Submitted to Phys. Rev.

MnSi-CoSiケイノジセイ : ヘンレキデンシケイニオケルラセンジセイ

京都大学0048新制・課程博士工学博士甲第1929号工博第520号新制||工||377(附属図書館)5284UT51-52-L246京都大学大学院工学研究科金属加工学専攻(主査)教授 中村 陽二, 教授 高村 仁一, 教授 村上 陽太郎学位規則第5条第1項該当Kyoto UniversityDA

Formation of a Hybridization Gap in a Cage-Like Compound CeFe2Al10

We report on the magnetic, transport, and thermal properties of a cage-like compound CeFe2Al10 that crystallizes in the orthorhombic YbFe2Al10-type structure. A broad peak in the magnetic susceptibility at 70 K indicates that CeFe2Al10 is a valence fluctuation compound. The electrical resistivity and the Hall coefficient exhibit sharp upturns below 20 K, where the thermopower shows a rapid decrease. These low-temperature anomalies in the transport properties resemble those of a typical Kondo semiconductor CeRhSb. These features indicate the formation of a hybridization gap in CeFe2Al10 on cooling below 20 K. The energy gap is estimated as 15K from the thermal activation energy of the resistivity. The magnetic contribution of the specific heat shows a Schottky-type maximum at 30 K that provides another evidence for the gap formation in CeFe2Al10