Domain observation in ferromagnetic and reentrant EuxSr1−xS

Abstract

Optical microscope observations have been made of magnetic domains in single crystals of EuxSr1−xS with the nominal value of x=1.0, 0.70, 0.54. No magnetization structure was seen for several lower values of x. Susceptibility measurements in the Curie–Weiss law regime and electron microprobe measurements were used to characterize the individual samples. The abrupt onset of visible magnetization structure on cooling provides a sensitive measure of TC. In striking contrast, on further cooling of a reentrant composition the contrast fades very slowly. Thus the change from ferromagnet to spin glass is spread over several tenths of a degree Kelvin. All of the crystals contain thin plate-like inclusions of a second Eu rich phase which represents less than about 0.1% of the volume. The observed domains differ considerably with Eu concentration. The salient characteristics may be summarized for nominal x=1.0: polygonal domains with M largely normal to the (100) sample plane; typical dimensions, 3–25 μm; x=0.7: magnetization lies in the plane with large prismatic closure patterns around each inclusion flake; domains are seen by magnetic birefringence contrast; x=0.54: extremely fine structure overall. Where organized by imperfections it is much coarser and more readily visible.