Study of the exchange anisotropy in the quantum chain systems (C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e11\u3c/sub\u3eNH\u3csub\u3e3\u3c/sub\u3e)CuCl\u3csub\u3e3\u3c/sub\u3e and (C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e11\u3c/sub\u3eNH\u3csub\u3e3\u3c/sub\u3e)CuBr\u3csub\u3e3\u3c/sub\u3e by means of (anti) ferromagnetic resonance

Abstract

\u3cp\u3eFerromagnetic resonance (FMR) measurements on the magnetic quasi-one-dimensional systems (C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e11\u3c/sub\u3eNH\u3csub\u3e3\u3c/sub\u3e) CuCl\u3csub\u3e3\u3c/sub\u3e (CHAC) and (C\u3csub\u3e6\u3c/sub\u3eH\u3csub\u3e11\u3c/sub\u3eNH\u3csub\u3e3\u3c/sub\u3e)CuBr \u3csub\u3e3\u3c/sub\u3e (CHAB) in the region 8< nu <75 GHz and at a temperature of 1.25K are presented. The experimental results can be described quite well by a classical mean-field model assuming that, in a first approximation, the ferromagnetic chains behave like independent entities. A comparison of this model with the experimental results yields accurate values for the exchange anisotropy. These values indicate a pronounced easy-plan anisotropy for CHAB, whereas for CHAC the inferred anisotropy is clearly orthorhombic. These results are in fair agreement with previously reported measurements of magnetisation and specific heat.\u3c/p\u3