Specific heat and magnetic phase diagram of Tb 1−xGd xB 2C 2

Abstract

Gd-substitution effects on the magnetic properties of an antiferromagnetic TbB 2C 2 with T N=21.7 K have been examined by the specific heat C( T) and magnetization M( B) of Tb 1− x Gd x B 2C 2. Magnetic B– T phase diagram of x=0.2 has been drawn by the results of C( T, B) and M( B). C( T) of x=0.1 has two anomalies at T 1=11.5 K and T N=21.7 K. T 1 increases faster than T N with increasing Gd concentration x, and two anomalies merge into one peak for x⩾0.35. A magnetic ground state for x⩾1 is (1 0 0)-type antiferromagnetic state. For 0< x⩽0.35, an intermediate magnetic phase whose propagation vector is (1+ δ δ 0) appears between T 1 and T N. For x=0.2, the other specific heat anomaly T 2 has been observed in the magnetic field applied along (1 0 0). A coexistent phase of an antiferromagnetic and a field-induced antiferroquadrupolar order has been found in the B– T phase diagram of x=0.2.