Magnetic hysteresis of granular high temperature oxide superconductors MBa2Cu2O7, where M = Y, Er, Dy, Ho, Lu, Tm, Gd, have been studied at 77 K by ESR technique and by vibrating sample magnetometer. The hysteresis curves reveal in both cases analogue features: They depend primarily on the direction of the field sweep and slightly on the external field and the sweep rates. Spin-glass properties have also been demonstrated. ESR baseline variation was interpreted in terms of the modulation of microwave absorption, and quantitative description was given for the transition curves between the upwards and downwards hysteresis lines. The ESR hysteresis contains a slow and a fast component and reveals field memory effects. Vortices formed by consecutive Josephson currents between superconducting grains are proposed to explain hysteresis phenomena: The flux uptake of outer loops with area 10-6-10-8cm2is related to the fast ESR hysteresis, while that of inner loops with area around 10-9cm2is related to the slow ESR hysteresis, the memory fading and the magnetization hysteresis.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Mathematical Physics
- Condensed Matter Physics