Pressure dependence of ${\mathrm{C}}_{4}{\mathrm{N}}_{2}{\mathrm{H}}_{4}$-mediated superexchange in $X{\mathrm{Cl}}_{2}{({\mathrm{C}}_{4}{\mathrm{N}}_{2}{\mathrm{H}}_{4})}_{2}\phantom{\rule{0.2em}{0ex}}(X=\mathrm{Fe},\mathrm{Co},\mathrm{Ni})$

Pressure dependence of $C_{4} N_{2} H_{4}$ -mediated superexchange in $X {Cl}_{2} {(C_{4} N_{2} H_{4})}_{2} (X = Fe, Co, Ni)$

J. Kreitlow, D. Menzel, A. U. B. Wolter, J. Schoenes, S. Süllow, R. Feyerherm, and K. Doll

Phys. Rev. B 72, 134418 – Published 20 October 2005

Abstract

We present measurements of the magnetic susceptibility $χ (T)$ on the pyrimidine bridged transition metal complexes $X {Cl}_{2} {(P)}_{2}$ ( $X = Fe, Co, Ni$ ; $P = pyrimidine$ ) under externally applied pressure. From our data we extract the pressure response of the antiferromagnetic phase transition at $6.4 K$ for $X = Fe$ , $4.7 K$ for $X = Co$ , and $16.3 K$ for $X = Ni$ . The experiments indicate that with a pressure of $\sim 8 kbar$ the transition temperature in all compounds increases by about 15%. Our data are complemented by electronic structure calculations, based on spin-unrestricted density functional theory. From these calculations we derive a bulk modulus $B_{0} = 20 GPa$ for $Fe {Cl}_{2} {(P)}_{2}$ , in reasonable agreement with the experimentally determined value of $15 GPa$ . Further, the calculations reproduce the antiferromagnetically ordered state as the ground state. Finally, we calculate the pressure response of $T_{N}$ for $X {Cl}_{2} {(P)}_{2}$ , $X = Fe, Ni$ , and derive an increase of $T_{N}$ by 16% and 9% for Fe and Ni, respectively, in good agreement with the experiments.