¹H NMR study of the layered antiferromagnet NH₄FeF₄

Abstract

1H NMR studies of the polycrystalline NH4FeF4 system in the temperature range 110-300 K reveal an anomalous increase in the line-width as well as the spin-lattice relaxation rate, T1-1 near the antiferromagnetic transition temperature 135 K. In the critical region, T1-1 diverges as epsilon -0.50, where epsilon =(T-TN)/TN. The exponent indicates pronounced 3D magnetic interaction near the transition point. However, the broad critical region (135 K<T<160 K) observed from the temperature dependence of T1-1 is an indication of the presence of 2D magnetic interaction.