Dependence of the Curie temperature of tetrakis-(para-tetradecyloxy-phenyl)-porphyrinatomanganese (III)-tetracyanoethenide (Mn-OC14-TCNE) on hydrostatic pressure to 21 kbar

Abstract The dependence of the Curie temperature on hydrostatic pressure has been determined to 21 kbar for the ferromagnetic molecular magnet (Mn(OC 14 H 29 ) 4 (TCNE), where Mn III -ions are situated in ferrimagnetic porphyrin chains separated by 31.2 A . In the present experiments both He-gas and piston-cylinder pressure systems are used to 6 and 21 kbar, respectively. Following an initial rapid decrease of the Curie temperature T c with applied pressure from 20 to 15 K at 1.5 kbar, T c abruptly begins to increase with pressure at an equally rapid rate, ultimately reaching nearly 37 K at 21 kbar. The change in the sign in d T c /d P at 1.5 kbar is likely the result of a phase transition in the spin and/or lattice system. The possible role of dipolar interactions in determining the magnetic state in a system of parallel ferrimagnetic chains is discussed.