Structure and magnetic studies of geometrically frustrated disordered pyrochlores A2Zr2O7: (A = Eu, Gd, Er)

Dy2Ti2O7 and Ho2Ti2O7 are the well-known spin ice systems where the replacement of Ti with Zr destabilizes the pyrochlore lattice and leads to the dynamic ground state. We have studied a series of disordered pyrochlore oxides A(2)Zr(2)O(7) (A = Eu, Gd, Er) and compared their crystal structure, magnetic, and heat capacity behavior with that of Dy2Zr2O7 and Ho2Zr2O7 systems. The analysis of the dc susceptibility curves suggests these systems as a frustrated antiferromagnet with negative Curie-Weiss temperature. Eu2Zr2O7 exhibited a temperature independent dc susceptibility in the range T = 20-90 K, which persist even at high fields due to the Van Vleck contribution. Gd2Zr2O7 and Er2Zr2O7 shows an unusual field-induced spin freezing anomaly near T asymptotic to 10 K which is similar to (Dy/Ho)(2)Zr2O7 systems. These studies show that depending on the disorder parameter, the spin-freezing behavior can be induced by slowing down the spin dynamic with a suitable choice of the magnetic field. We observed that, unlike titanates, modification at the rare-earth site does not make a considerable change in the magnetic ground state of these Dy, Ho, Er, Gd based zirconates compounds.