Isothermoremanent magnetization and its relaxation with time have been investigated in ceramics and powders of YBa 2 Cu 3 O 7−δ at different temperatures after magnetizing the sample in a field of H ext eff ≈0.7 eV, independent of H ext . In the ceramic material U eff was found to depend strongly on the applied field reaching a value of 5 eV at 10 Oe and decreasing steeply when the magnetizing field was increased. The field dependence is discussed by using a model which takes into account the interaction between vortices.

Trapping and relaxation of inter- and intragrain vortices in YBa2Cu3O7−δ

Magnetic freezing near 200 K in the semimagnetic semiconductor (Cd1−xMnx)3As2

Magnetic phase diagram and dynamics of low-temperature magnetic behaviour of the CoAl1−xCux system

(Cd1-xMnx)3As2 (CMA) is a semimagnetic n-type semiconductor with Eg approximately=-0.095 eV. Magnetic susceptibility measurements in single crystals of CMA show that in weak applied fields (H or=0.04 and is attributed to presence of large magnetic clusters in the sample. From the data of the thermoremanent magnetization it is suggested that some of them can remain up to temperatures much higher than Tf.

High-temperature magnetic freezing in (Cs1-xMnx)3As2

Relaxation of the isothermoremanent magnetization has been investigated in ceramic Y-Ba-Cu-O samples with different grain sizes. It is found that the effective pinning energy U eff determined at different temperatures by using relaxation data of the remanent magnetic moment M IR and the relationship dln M IR / dln t =- kT / U eff has a maximum at a value of the magnetizing field H 0 corresponding to the most rapid increase of M IR with increasing H 0 . A phenomenological theory based on a critical- state model has been developed to describe these phenomena. The main conclusion of our analysis is that the dependence of U eff on H 0 can be attributed to the evolution of the distribution of the trapped flux (as H 0 is varied) without involving any assumptions about the dependence of the pinning barrier on the field.

Influence of the spatial distribution of trapped magnetic flux on the effective pinning energy of vortices in ceramic Y-Ba-Cu-O

Magnetic investigations of the electron-doped superconductor Nd2-xCexCuO4 (with nominal composition x=0.15) are reported. In a low external field (5 G) the normal state susceptibility obeys the Curie-Weiss law but in higher fields a deviation from this behaviour is observed at T approximately=40 K. From the high-temperature data the value of the Curie temperature theta =-70 K is obtained, indicating antiferromagnetic interactions. Hysteresis measurements give the critical current density of jc=2.3*102 A cm-2 in a field of 30 G. From the logarithmic time dependence of the thermoremanent magnetisation we estimate an activation energy of Uo=0.05 eV for thermally induced flux creep.

A Pajaczkowska

Papers

Magnetic and superconducting properties of Nd1.85Ce0.15CuO4