Specific heat and magnetic phase diagram of Tb1−xGdxB2C2

Abstract Gd-substitution effects on the magnetic properties of an antiferromagnetic TbB 2 C 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 2 C 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.