No abstract

The optical linear magnetic birefringence (LMB) of cobalt oxide single crystals was determined as a function of temperature near the antiferromagnetic NBel point. The measurements were taken from single-domain crystals with the tetragonal c-axis oriented parallel or perpendicular to the direction of the light beam. Below T, the change of LMB with temperature in perpendicular arrangement is found to be proportional to the c-axis contraction and to the square of the long-range order parameter. t. IntroductionRecently several authors have reported birefringence in materials with magnetic phase transitions [l to 31. It was shown that the birefringence is due to magnetic ordering of the material in all cases. For the transition metal fluorides Jahn [l] found that linear magnetic birefringence (LMB) is connected with the magnetic specific heat. However, since these materials are naturally birefringent, the experiments were difficult to interpret, especially for temperatures above the NBel point.Transition metal oxides, such as MnO, COO, and NiO, which in the paramagnetic phase have NaCl structure and whence no natural birefringence, should lack these drawbacks. We have performed experiments on COO which undergoes a paramagetic-antiferromagnetic phase transition between 288 and 295 K depending on the type of measurement [4]. This magnetic ordering is coupled with a strong tetragonal [5] and a much weaker rhombohedra1 [B] lattice distortion. Below the NBel temperature the ferromagnetic sheets in COO are parallel to the (111) planes, whereas the spin direction is [II7], nearly parallel t o the c-axis which is [OOl].

No abstract

No abstract

No abstract