Anomalous magnetization cycle of UFe4Al8 single crystals: A Mossbauer effect study

An Fe-57 Mossbauer spectroscopy study was performed on an UFe4Al8 single cr ystal, in an external magnetic field B-ext, subtending an angle of 11 degre es at the b axis. It shows that, even in low fields, the configuration of t he Fe magnetic moments, mu(Fe), is consistent with the canted antiferromagn et ic order of mu(Fe), established by single-crystal neutron diffraction in a field of 4.6 T. The canting of mu(Fe) is always observed towards the dir ection of the U magnetic moments mu(U), clearly showing that it is induced by mu(U) rather than by B-ext. At a certain value of B-ext during the magne tic domain rotation, the direction of mu(Fe) is found to be temporarily fro zen approximately along the direction of B-ext. This confirms previous magn etization and magnetoresistance data, which show that for the same values o f B-ext, mu(U) is blocked perpendicularly to B-ext. Furthermore, the presen t study reveals that this blocking is a metastable state with a relaxation time of a few hours, at 4.2 K. [S0163-1829(99)03230-0].