OBSERVATION OF TRANSITIONS TO SPIN-SLIP STRUCTURES AND SPLITTING OF THE NEEL TEMPERATURE OF HOLMIUM IN MAGNETIC-FIELDS

We present the results of magnetization measurements on single-crystal holmium using a SQUID magnetometer in the temperature range from 4 to 140 K in magnetic fields up to 5.5 T. In low fields (0.01 T) the magnetization versus temperature data show a spiral to conical transition at Tc=16 K and the Néel temperature at 132 K. In addition, we observe new anomalies in the temperature dependence of the magnetization along the a, b, and c axes at 20, 24, 42, and 98 K. These new anomalies appear at the same temperatures as observed by Bates et al. [J. Phys. C 21, 4125 (1988); 21, 4113 (1988)] in ultrasonic velocity measurements on holmium. These anomalies could be accounted for within the frame work of the "spin-slip" model of Gibbs and co-workers. In the c axis magnetization we observe a splitting of the Néel temperature in magnetic fields greater than 0.5 T. The H-T phase diagrams of the magnetic phases of holmium for fields in three directions (along the a, b, and c axes) are presented.