Hazuki Kawano

Magnetic Behavior of a Mott-Insulator YVO3

As one of the members of the ABO 3 -type pseudoperovskite oxide family, Y 1- x Ca x VO 3 exhibits an insulator-metal transition upon a change in the dopant calcium ion concentration x . We have reinvestigated the magnetic structure of the parent compound YVO 3 with use of the neutron scattering technique. YVO 3 orders at T N1 =118 K with the so-called C-type antiferromagnetic structure, but changes to the G-type antiferromagnetic structure at T N2 ∼77 K through a first order transition with lattice distortion. These spin structures differ from those of an early study by Zubkov et al . (Sov. Phys.-JETP 39 (1974) 896). The static moment which contributes to the magnetic long range order is extrapolated to be less than 1.6 µ B at T =0 K. This value of the static moment is more than 20% smaller than 2.0 µ B expected for a localized spin system with S =1, indicating the existence of spin fluctuations in a Mott insulator YVO 3 .

Two successive spin glass transitions in nondiluted Heisenberg-like spin glass Ni0.42Mn0.58TiO3

Two successive spin glass (SG) transitions were observed in a nondiluted Heisenberg-like SG system with a weak planar single-ion anisotropy, Ni 0.42 Mn 0.58 TiO 3 . The moment lying in the easy plane freezes at T ∥ S G =9.5±1.0 K, while the remaining component perpendicular to the easy plane freezes at a lower temperature T ⊥ S G =6.0±0.5 K, being consistent with theory on the Heisenberg-like SG system having a weak single-ion anisotropy. The diffuse scattering profile is well described by a Lorentzian in an intermediate phase T ∥ S G ≥ T > T ⊥ S G as well as in a paramagnetic phase T > T ∥ S G , whereas it strongly deviates from the Lorentzian below T ⊥ S G .

Magnetic phase transitions of ErCu2

Abstract ErCu 2 has a first-order magnetic phase transition at 6.1 K ( T t ) below the Neel temperature of 11.3 K. The spin structure above T t is a transversely modulated square-wave type structure with wave vector 5 13 a * and moments along the b -axis. Then an anti-phase-domain modulation with wave vector 1 18 c * adds to above structure below T t .

Two-dimensional anisotropy in a layered metallic antiferromagnet RE1−xSrxMnO3 with x ∼ 12

Abstract Some RE1-xSrxMnO3 (RE  Nd, Pr) systems with x ∼ 1 2 exhibit an A-type antiferromagnetic (AFM) structure instead of the expected CE-type magnetic structure. This can be understood as being a consequence of the increase of the bandwidth (W). These A-type magnetic systems also show salient features in their crystal structures. We propose a two-dimensional anisotropy of the transport as well as the magnetic properties for the A-type AFM structure and we show that we have, indeed, observed anisotropic spin wave dispersion relations by inelastic neutron measurements.

ANOMALOUS PHONON PROPERTIES IN THE INTERMETALLIC SUPERCONDUCTOR YNI211B2C

Abstract YNi211B2C shows a new phonon peak in the superconducting state. Recently, an alternative interpretation for the change of the scattering function in the superconducting phase, a “narrowing” scenario, was proposed. In this paper we carefully examine the phonon profiles and present evidence that supports our “new peak” scenario.

Neutron diffraction study of ErCu2

Abstract Neutron diffraction measurements were performed on single-crystal ErCu2. The magnetic structure was deduced to be square-wave-type antiferromagnetic with propagation vector (0.385, 0, 0). The propagation vector changes to a two-dimensional one below 6.1 K, through a first-order phase transition.

Phase Diagram of a Reentrant Ising Spin Glass Fe0.6Mn0.4TiO3 on the Magnetic Field-Temperature Plane

Behavior of the reentrant spin glass (RSG) material Fe 0.60 Mn 0.40 TiO 3 in magnetic fields H <7.1 kOe is studied by neutron scattering technique, and the H - T phase diagram was constructed. For H ≥0.93 kOe, the random field (RF) induced history dependent behavior was observed between zero-field-cooled (ZFC) measurements and field-cooled (FC) measurements below the Neel temperature T N ( H ). By examining the behavior of Bragg and diffuse scattering in ZFC measurements, the RSG transition temperature T RSG is determined. One finds that it appears within a gradual crossover region from weak irreversibility to SG-induced strong irreversibility observed in the previous magnetization measurements. The initial slope of the T RSG line is perpendicular to the temperature axis.

Interplay between magnetism and superconductivity in HoNi211B2C

Abstract We have studied magnetic properties of an intermetallic superconductor HoNi211B2C (TC = 7.0 K). In this paper, we will discuss a role of magnetic ordering on superconductivity in this system.

Phonon anomalies in YNi211B2C

Recently we have discovered a new peak with phonon character which appears only below Tc in an intermetallic superconductor, YNi211B2C (Tc∼14-2K) by neutron inelastic scattering measurements. The peak intensity of the new peak shows the order-parameter-like temperature dependence of the superconductivity. The new peak grows by absorbing the spectral weight from the above-lying soft phonon mode. In the present study we investigate the magnetic field dependence of the new peak. With increasing magnetic field, the new peak is gradually suppressed and disappears by H=Hc2 (∼4.7T at T=5.5K). Beyond Hc2, the profile of the scattering function recovers that of the non-superconducting state above Tc These results strongly indicate that this new peak is undoubtedly associated with the superconducting state in YNi211B2C.Recently the authors have discovered a new peak with phonon character which appears only below T{sub c} in an intermetallic superconductor, YNi{sub 2} {sup 11}B{sub 2}C (T{sub c} {approximately} 14.2K) by neutron inelastic scattering measurements. The peak shows the order-parameter-like temperature dependence of the superconductivity. The new peak grows by absorbing the spectral weight from the above lying soft phonon mode. In the present study they investigate the magnetic field dependence of the new peak. With increasing magnetic field, the new peak is gradually suppressed and disappears by H=H{sub C2} ({approximately}4.7T at T=5.5K). Beyond H{sub C2}, the profile of the scattering function recovers that of the non-superconducting state above T{sub c}. These results strongly indicate that this new peak is undoubtedly associated with the superconducting state in YNi{sub 2}{sup 11}B{sub 2}C.

Magnetic excitations in diluted Ising antiferromagnet Fe1−xMgxTiO3

Abstract Inelastic neutron scattering experiments have been carried out in the diluted Ising antiferromagnet Fe1−xMgxTiO3 with x = 0.1 and 0.2. Two non-degenerate acoustic magnon branches were observed in both of the samples, which are similar to the result for the sample with x = 0 previously reported. The zone-center gap energy of the lower energy branch increases with increasing Mg concentration x.