Crossover from one- to three-dimensional behavior in theS  =  1/2 Heisenberg antiferromagnet Cu(N₂H₅)₂(SO₄)₂

Abstract

From experimental and theoretical analyses of magnetic and specific-heat properties, we present the complete magnetic phase diagram of the quasi-one-dimensional antiferromagnet Cu(N 2 H 5 ) 2 (SO 4 ) 2 . On cooling and at zero magnetic field this compound enters a one-dimensional regime with short-range magnetic correlations, marked by a broad maximum in the specific heat and magnetic susceptibility at T ∼ 2 K, followed by a tridimensional antiferromagnetically ordered phase below T ∼ 1 K induced by small interchain couplings. The intermediatetemperature one-dimensional regime can be modeled using exact quantum-transfer-matrix calculations, which offer a compatible description of the nonmonotonic behavior of T as a function of the magnetic field, giving = 4.25 K for the intrachain exchange parameter. The analysis of magnetic specific-heat and susceptibility data at low temperature indicates that the interchain exchange couplings are an order of magnitude smaller than the coupling inside the chains.2