A. Ito

Mössbauer study of YBa2 (Cu1-xFex)3O7-δ : Superconductivity and magnetic order

Abstract The electronic and magnetic properties of the ceramic superconductor YBa2 (Cu1-xFex)3O7-δ with x =0.010, 0.017, 0.033 and 0.067 have been studied microscopically by Mossbauer technique. We have shown that Fes are substituted for both Cu 1 and Cu 2 sites. We have also shown that the samples with x >; 0.01 undergo a magnetic transition at low temperatures without destroying the superconductivity, and that the magnetic transition temperature TM increases with x. The coexistence of the superconductivity and the magnetic order is discussed, and it is argued that spin fluctuations of Cu are related to the superconductivity.

Phase diagram and reentrant spin-glass behavior in a random mixture of two Ising-antiferromagnets FexMn1−xTiO3

Abstract Low-field DC susceptibility measurements have been made on a random-mixture of two Ising-antiferromagnets Fe x Mn 1−x TiO 3 . A spin-glass state appears in a wide range of intermediate concentration. In samples with certain x in the Fe-rich side or the Mn-rich side, the reentrant transition from the antiferromagnetic state or the random-antiferromagnetic state is found to occur. The reentrant behavior appears drastically, which we attribute to the strong frustrations existing in a magnetically non-diluted short-range system. The concentration versus temperature phase diagram is also shown.

Studies on spin-glass freezing and antiferromagnetic long-range order in an Ising spin-glass system Fe x Mn1−x TiO3

A Mössbauer time window has been positively used for studying the behavior of spins in FexMn1−xTiO3 withx=0.50, 0.60 and 0.65 which are of typical Ising spin-glass systems. Spin dynamics aboveTSG andTN (RSG) (definition is given in the text) are discussed. In the RSG samples, the existence of contributions of the transverse spin component to the hyperfine fields is pointed out.

Spin dynamic in mixed antiferromagnet with competing anisotropies Fe0.6Co0.4TiO3 probed by positive muons

Abstract The positive muon spin relaxation method is applied to probe the spin dynamics in the random mixture of two antiferromagnets with competing anisotropies Fe 0.6 Co 0.4 TiO 3 . In the S ∥ -ordered phase between the paramagnetic phase and the oblique antiferromagnetic phase, the characteristic relaxation is observed, revealing that the spin component S ⊥ which has not a long-range order is dynamically fluctuating. The correlation time of this fluctuated spin component is estimated to be 10 −7 ∼10 −5 s .

New method for accurate analysis of Mössbauer spectra of YBa2(Cu1−xFex)3O7−δ

Abstract A new technique for accurate analysis of complicated Mossbauer spectra of YBa 2 (Cu 1−x Fe x ) 3 O 7−δ has been introduced, and the Mossbauer spectrum of YBa 2 (Cu 0.95 Fe 0.05 ) 3 O 7−δ at room temperature is decomposed into four kinds of quadrupole doublets and their quadrupole splittings ΔE Q and the center shifts δ are determined precisely. We have shown that the values of ΔE Q for the doublets D-3 and D-4 (defined in the text) reported previously by many groups of workers should be changed.

Spin glass behavior probed by various methods with different time- and space-scale of observation: Ising spin glass Fe0.50Mn0.50TiO3

Under the expectation that the behavior of a spin glass (SG) system shows various aspects depending on the time- and space-scale of observations, we have studied the typical Ising spin glass Fe0.50Mn0.50TiO3 by measuring dc-magnetization, ac-susceptibility, Mössbauer spectrum, neutron scattering intensity and μ+SR time spectrum. We have demonstrated that the application of various methods with different time- and space-scale of observations to the same system is useful to clarify the property of the spin glass freezing, the Ising character and the de Almeida and Thouless-line.

Mössbauer study on Fe-sitting site and origin of magnetic order in YBa2(Cu0.95Fe0.05)3O7−δ

Fe-sitting sites and the origin of magnetic order in YBa2(Cu0.95Fe0.05)3O7−δ have been studied by comparing the Mössbauer spectra observed before and after heat-treatments at 300°C in vacuum. Both of the major quadrupole doublets D-1 and D-2 are assigned to originate from Fe’s replacing Cu1’s. It is also suggested that fluctuations of Cu2 spins play an important role for inducing the magnetic order.

Mössbauer studie of Co2B by doping 1 at %57Fe

In order to clarify the direction of the easy axis of Co2B, we examined Co2B doped with 1 at %57Fe using Mössbauer spectroscopy. In the temperature range 4.2 K≤T≤r.t., two well resolved six-line patterns having equal intensity were observed. This shows that the easy axis lies in the c plane. The displacement of magnetically split absorption lines by quadrupole interaction also supports this conclusion. In the temperature region between 4.2 K and 1.6 K, the direction of the easy axis seems to begin to deviate from the c plane.

Mössbauer study on a two-dimensional random mixture with competing spin anisotropies K2Ni1−x Fe x F4

Mössbauer measurements have been made on a two-dimensional (2D) random mixture K2Ni1−xFexF4 with competing spin anisotropies. The concentration versus temperature phase diagram predicted by Oguchi and Ishikawa for mixed systems with competition between orthorhombic anisotropies has been shown to exist in K2Ni1−xFexF4. The coexistence of two kinds of Mössbauer spectra is seen in the transition regions, and is believed to be an intrinsic property of this system.

Magnetic states of Cu1 sublattice in YBa2Cu3Oy high Tc compounds at different oxygen content

Magnetic states of Cu1 sublattice in YBa2Cu3Oy: 1%57Fe compounds with 6.09 ≤y≤6.98 were investigated by57Fe Mössbauer spectroscopy at 1.68≤T≤300 K. It has been found that, upon reducingy, the magnetic transition temperatureTml changes from 3.3 to 12 K aroundy≃6.4 where the superconductivity disappears. The magnetic phase diagram for the Cu1 sublattice is plotted.