NMR Study of Nearly Two-Dimensional Ferromagnet (C_<i>n</i>H_2<i>n</i>+1NH₃)₂CuCl₄(<i>n</i>=1∼4) at Low Temperature

Abstract

NMR of Cl 35 nuclei (within layer) of (C n H 2 n +1 NH 3 ) 2 CuCl 4 is observed at the magnetically ordered state. Through the angular dependence of the NMR frequency, the crystallographic structure of the CuCl 4 layer is determined, which is slightly different from the known crystal structure at room temperature. The existence of various moment directions is shown in (C 3 H 7 NH 3 ) 2 CuCl 4 . The magnetic coupling between layers is discussed. The observed magnetization of (C n H 2 n +1 NH 3 ) 2 CuCl 4 ( n =1, 3 and 4) is compared with the renormalized spin wave theory. It is also shown that the magnetization follows the “T 3/2 -law” given as, <S>/S=1-α(T/T c ) 3/2 , with α∼0.45. The field dependent behavior of the magnetization of (C 2 H 5 NH 3 ) 2 CuCl 4 is discussed at antiferromagnetic state.