Irreversible magnetization in thin YBCO films rotated in external magnetic field

Abstract

The magnetization M of a thin Y Ba 2 Cu 3 O 7−δ film is measured as a function of the angle θ between the applied field H and the c− axis. For fields above the first critical field, but below the Bean's field for first penetration H * , M (θ)is symmetric with respect to θ = π and the magnetization curves for forward and backward rotation coincide. For H > H * the curves are asymmetric and they do not coincide. These phenomena have a simple explanation in the framework of the Bean critical state model.

Irreversible magnetization under rotating fields and lock-in effect on a ErBa2Cu3O7-δ single crystal with columnar defects

“…It has been shown [9][10][11] that, in this fully penetrated critical state and as long as ν tan Θ ≪ 1, the angle between M i and the sample normal n is α ∼ arctan 2 3 ν 2 tan Θ ≪ Θ. That is, M i remains almost locked to n due to a purely geometrical effect.…”

“…A rotation at fixed H is to some extent analogous to a hysteresis loop 9 . Rotating n towards H increases H ⊥ , which is roughly equivalent to increasing H at Θ = 0 • , moving along the lower (diamagnetic) branch of the loop.…”

“…This suggests that, at least to a first approximation, collective effects in the range of our measurements simply result in a different prefactor in eq. (9). Clearly, lock-in effects in the collective regime deserve further theoretical study.…”

“…Equation (9) predicts that ϕ L should be inversely proportional to H. The improved resolution of the rotation measurements, that permits a much better determination of the width of the plateau, allows us to test this dependence. To that end, we have measured several other sets of data similar to Figure 3(b), for a wide range of temperatures (35K to 85K).…”

Magnetization rotation in YBCO thin films: deviations fromc-axis scaling

“…Experiments have generally shown good agreement [12,13] with the critical state model despite the effects of vortex curving. In particular it has been shown by Prozorov et al [14] that the critical state magnetization of thin films is contributed overwhelmingly by the component parallel to the c-axis and that the a-b-plane moment is negligible. This has been further elaborated by Zhukov et al [15] who showed that this effect originates in the extremely large aspect ratio of the thin films.…”