Magnetic Interaction and Phase Transition in the Organic Free Radical TANOL in Hydrostatic Pressures

Abstract

Hydrostatic pressure dependence of the magnetic transition temperature T_N(p) and interactions in the organic free radical TANOL(2,2,6,6-tetramethyl-4-piperidinol-1-oxyl), a quasi-one-dimensional Heisenberg antiferromagnet, has been studied by the heat capacity measurements in the pressure range p<6 kbar at low temperatures. The values (1⁄T_N(p₀))dT_N(p)⁄dp\simeq0.15 kbar⁻¹, (1⁄J(p₀))dJ(p)⁄dp\simeq0.076 kbar⁻¹ and (1⁄J′(p₀))dJ′(p)⁄dp\simeq0.22 kbar⁻¹ obtained here turn out to be the largest of the corresponding values in the magnetic systems ever studied, where J(p) and J′(p) are the intra- and inter-chain interaction constants, respectively (p₀\simeq0.001 kbar). The dependence of these interactions on the distance between the adjacent magnetic spins is suggested much stronger than the usual 10-th power law for the superexchange mechanism in inorganic magnetic systems.