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ABSTRACT: Quantum-critical behavior of the itinerant electron antiferromagnet (V0.9Ti0.1)2O3 has been studied by single-crystal neutron scattering. By directly observing antiferromagnetic spin fluctuations in the paramagnetic phase, we have shown that the characteristic energy depends on temperature as c1 +c2T3/2, where c1 and c2 are constants. This T3/2 dependence demonstrates that the present strongly correlated d-electron antiferromagnet clearly shows the criticality of the spin-density-wave quantum phase transition in three space dimensions.
Physical Review Letters 09/2008; 101(9):096406. · 7.37 Impact Factor
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ABSTRACT: 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$60 K but remains finite in the low-temperature limit. Comment: 9 pages, 4 eps figures; corrected the author list
11/2001;
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ABSTRACT: We report the observation of nuclear quadrupole resonance (NQR) of Cu from the sites near the doping center in the spin-Peierls system CuGe$_{1-x}$Si$_{x}$O$_3$. The signal appears as the satellites in the Cu NQR spectrum, and has a suppressed nuclear spin-lattice relaxation rate indicative of a singlet correlation rather than an enhanced magnetic correlation near the doping center. Signal loss of Cu nuclei with no neighboring Si is also observed. We conclude from these observations that the doping-induced moments are not in the vicinity of the doping center but rather away from it. Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Lett
08/2001;
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ABSTRACT: Low-frequency spin dynamics in the S=1/2 antiferromagnetic spin-chain compound \alpha-VO(PO_3)_2 has been studied by means of 31P NMR. The nuclear spin-lattice relaxation rate 1/T_1 at the P site exhibits H^{-1/2} dependence on the applied magnetic field (H) at temperatures (T) well above the intrachain coupling strength J/k_{B} = 3.50 K indicating one-dimensional diffusive spin dynamics. The diffusive contribution to 1/T_1 decreases on cooling as electronic spins acquire short-range antiferromagnetic correlations within the chain, and vanishes almost entirely around T \approx J/k_{B}. This is accompanied by an apparent increase of the spin-diffusion constant from the value expected in the classical limit. On the other hand, the field-independent part of 1/T_1 increases with decreasing temperature, which may be a precursor for the true long-range antiferromagnetic ordering found below T_{N} = 1.93 \pm 0.01 K. Comment: 9 pages, 11 embedded eps figures uses JPSJ.sty, revised for publication in J. Phys. Soc. Jpn
02/2001;
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ABSTRACT: Magnetic properties of a quasi one-dimensional magnet CuV_2O_6 have been studied by means of susceptibility measurement, NMR and powder neutron diffraction. Cu^{2+} spins (S=1/2) order antiferromagnetically below 22.6 K, and the saturation moment is about 0.70 \mu_{B} at 0 K. The magnetic structure determined in the present study indicates that in CuV_2O_6 one-dimensional antiferromagnetic spin chains are along [110], suggesting a dominant antiferromagnetic exchange interaction between the next-nearest-neighbor spins rather than the nearest-neighbor ones. Comment: 9 pages, 12 embedded eps figures uses JPSJ.sty, accepted for publication in J. Phys. Soc. Jpn
04/2000;
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ABSTRACT: 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. B
02/1999;
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ABSTRACT: 63,65Cu NMR and NQR measurements have been performed to study the Cu2+ electronic state and the spin dynamics in CuGeO3, which is an inorganic compound that undergoes the spin-Peierls transition at Tsp∼14 K. The NQR frequency is discussed in connection with the lattice dimerization accompanied by the spin-Peierls transition. The Knight shift with an axial symmetry showed the temperature dependence corresponding to the reduction of the spin susceptibility. From the analysis of the Knight shift and the magnetic susceptibility, orbital and spin susceptibilities are evaluated. The analysis of the hyperfine structure leads to a conclusion that the electronic state of the Cu2+ ion above Tsp is described by a single-ion model in a crystal field with a tetragonal symmetry. The supertransferred hyperfine interaction, which is one of the characteristic features of Cu2+ ions in the CuO2 plane in the high-Tc superconducting copper oxides, is found not to play an important role in CuGeO3. The temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 clearly shows presence of a gap in the magnetic excitation spectrum below Tsp. The relaxation mechanism is discussed based on the spinless fermion treatment for an S=1/2 one-dimensional Heisenberg antiferromagnet (1DHAF) above Tsp and for a nonuniform S=1/2 1DHAF with two unequal and alternating exchange interactions below Tsp. Above Tsp, it is also discussed in terms of the dynamical susceptibilty of the 1DHAF.
Phys. Rev. B. 07/1995; 52(5).
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ABSTRACT: Magnetic properties of La1-xSrxCoO3 (0
≤x ≤0.5) have been studied by magnetization measurements in low
magnetic fields. It has been found that there exist spin-glass (0<x
≤0.18) and cluster-glass (0.18 ≤x≤0.5) regions. Ferromagnetic
long-range order previously reported does not take place. Spin-glass
behavior is ascribed to the frustration of random competing exchange
interactions, namely the ferromagnetic double-exchange interaction
between Co3+ and Co4+ and the antiferromagnetic
one between like spins.
Journal of the Physical Society of Japan 03/1994; 63:1486. · 2.36 Impact Factor
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ABSTRACT: We performed magnetization, neutron scattering and NMR measurements to reveal the hole-doping effect on magnetic properties of La1−xSrxCoO3 (0 ≤ x ≤ 0.5). A magnetic phase diagram which includes spin-glass (0 ≤ x ≤ 0.18) and cluster-glass (0.18 ≤ x ≤ 0.5) phases is proposed.
Journal of Magnetism and Magnetic Materials.
