Nonlinear magnetic susceptibility and microwave spin dynamics of R2CuO4 quasi-2D antiferromagnets (R=Eu, Pr, Gd)

An experimental study of nonlinear ac magnetic susceptibility and microwave spin dynamics of R2CuO4 quasi-2D Heisenberg antiferromagnets (R = Eu, Pr, Gd) has been carried out. The data obtained can be accounted for if one ass umes the existence of a random-field (RF) state in the Eu2CuO4 and Pr2CuO4 tetragonal crystals within the 77 less than or equal to T less than or equa l to 350 K range covered. If this is so, 3D antiferromagnetic order persist s only within limited regions, while in CuO2 layers there are 2D Heisenberg antiferromagnetic spin fluctuations with large correlation lengths. In the Gd2CuO4 crystal there exists, besides uniform 3D antiferromagnetic long-ra nge order with weak ferromagnetism, an admixture of an RF-type state. (C) 1 999 American Institute of Physics. [S1063-7834(99)01808-0].