Low temperature spin reorientation in dysprosium iron garnet

The spin reorientation (SR) phase transition in dysprosium iron garnet (Dy3Fe5O12 or DyIG) have been studied by specific heat C-p(T) and high field magnetisation measurements M-T(H) and M-H(T) on single crystals at low temperature. A first order SR is observed with a sharp jump at T-SR=14.5+/-0.5 K in the C-p(T) curve which corresponds to a spontaneous change from the high temperature (HT) easy direction < 111 > to an < uuw > angular low temperature (LT) phases. Above T-SR, the magnetic structure is described by the irreducible representation (IR) A(2g) of the rhombohedral space group R (3) over barc. Below T-SR, the magnetic structure changes in the monoclinic the space group C2/c with the IR A(g). When the field H is kept aligned along the hard symmetry directions < 100 > and < 110 >, we obtain respectively the variation of the angular positions theta(T) and theta '(T) from the total spontaneous magnetisation down to 1.5 K (theta=39.23 degrees and theta '=30.14 degrees) and the results are in good agreement with the previous observations in low fields. When the sample is allowed to rotate freely on itself, the critical field H-c(T) between the HT < 111 > and the LT < uuw > angular phases permits us to precise the transition line up to 15 T and 40 K between the so called canted field induced (FI) and the associated collinear magnetic phases. The experimental magnetic phase diagram (MPD) is precisely determined in the (H-c-T) plane and the domains of the existence and the stability of the two magnetic phases are specified.