Magnetic and thermal properties of dysprosium aluminum garnet. III. Multiaxis phase transitions

Dysprosium aluminum garnet is a cubic antiferromagnet with highly anisotropic moments along $\pm x$, $\pm y$, and $\pm z$ directions. In weak magnetic fields applied along any direction the zero-field antiferromagnetic state is stable. In strong magnetic fields, of the order of 10 kOe, applied along [110] or [001], those spins with a component along the field are driven paramagnetic. Because of the unusual symmetry of the magnetic lattice, the remaining (transverse) spins are decoupled from the others and are ordered at low temperatures by their own spin-spin interactions. We have investigated the magnetic phase diagrams with fields along [110] and [001] by making specific-heat and susceptibility measurements from 0.4 to 4.2 K in applied magnetic fields as large as 15 kOe. Specific-heat measurements were also made for fields slightly misaligned from [001], and the entire (110) plane was studied by adiabatic field rotation. The phase boundaries separating the simple antiferromagnetic and paramagnetic states contain tricritical points; the first-order portion of the phase boundary and the associated latent heat were measured by isothermal demagnetizations and magnetizations. We have analyzed the data to extract the critical fields and other characteristic parameters for both the simple antiferromagnetic phase as well as the "transverse" ordered states.