Abstract: First-order transitions in the magnetization of single crystal Fe films

Abstract

The magnetization curves of single crystal Fe films exhibit discontinuities as a function of applied field, for particular field directions, indicative of first-order phase transitions. M-H phase diagrams of cubic ferromagnets like Fe with three easy axes are predicted to show a variety of phase transition and multicritical points. They are of special interest in the region H ∥ [111] where the three-state Potts model should apply. Single crystal films were obtained by epitaxial growth on GaAs.1 These films are oriented (11̄0) surfaces containing easy [100], hard [111], and intermediate [110] cubic axes. The restricted geometry of the films does not change the mean field phase diagram for field orientations in the (11̄0) plane between [001] and [111]. However, for in-plane field orientations between [111] and [110] demagnetizing effects prevent the moment from being stabilized along the nearest easy axis by small fields and produce first-order phase transitions not seen in the three-dimensional phase diagram. In particular, the maximum discontinuity and the minimum applied critical field are predicted to occur along [110]. The data are consistent with mean field predictions except that the onset of the first-order discontinuities does not occur until the field is rotated somewhat beyond [111] toward [100]. This modification is obtained by the introduction of an additional anisotropy in the plane of roughly the same order of magnitude as the fourth-order cubic anisotropy. The required magnitude is consistent with the magnetoelastic energy from growth induced strain. A complete account of this work is published elsewhere.2 1 G. A. Prinz and J. J. Krebs, Appl. Phys. Lett. 39, 397 (1981). 2 K. B. Hathaway and G. A. Prinz, Phys. Rev. Lett. (in press).