Specific heat of geometrically frustrated and multiferroic RMn1−xGaxO3 (R=Ho,Y)

Specific heat measurements on single crystals of RMn1−xGaxO3 (R=Ho,Y) have revealed that Ga doping raises the Mn-spin reorientation temperature TSR while lowering the antiferromagnetic ordering temperature, TN, of the Mn spins and the Ho magnetic ordering temperature T2. The variations of the calculated magnetic entropy with Ga doping show the existence of spin fluctuations above TN in the geometrically frustrated Mn-spin system and a coupling between the Mn3+-ion and Ho3+-ion spins both at TSR and T2. The data also support Schottky anomalies in the specific heat of HoMn1−xGaxO3, which is dominated by crystalline electric fields but also affected by Mn3+-ion spin orderings. The large electronic contribution to specific heat of HoMnO3, γ, is suggested to be due to Ho3+ spin disorder.