Pressure response of the bimetallic chain compound MnNi(NO2)4(en)2;: en = ethylenediamine

The compound MnNi(NO2)(4)(en)(2), en = ethylendiamine, is a rare example of a ferromagnetically coupled bimetallic chain (J(broken vertical bar broken vertical bar chain) similar to 2-3 K). Further, for this material, a finite inter-chain coupling triggers an antiferromagnetic (AFM) transition below T-N, = 2.3 K. Here, we present a susceptibility study of MnNi(NO2)(4)(en)(2) under pressure. From our data, we derive the pressure response of the antiferromagnetic transition temperature TN. Even Lip to highest pressure of 8.2 kbar we find a very modest increase of T-N, by only similar to 0.1 K. Independently, from a pressure study of the lattice parameters of MnNi(NO2)(4)(en)(2), We calculate the bulk module of the material to similar to 8.8 GPa. Combining the data T-N(p) with the bulk module yields an anomalously low Graneisen parameter Gamma(mag) of only 0.5(5). We discuss possible scenarios accounting for such a low Gruneisen parameter. (c) 2005 Elsevier Ltd. All rights reserved.