Pressure induced transition from spin glass-like behavior to a metamagnet exhibiting weak ferromagnetism observed for decamethylferrocenium hexacyanobutadienide, [FeCp*2]˙+[HCBD]˙−

Abstract

The magnetic properties of [Fe(III)Cp*2]˙(+)[HCBD]˙(-) (Cp* = pentamethylcyclopentadienide; HCBD = hexacyanobutadienide, C4(CN)6) and [Fe(III)Cp*2]˙(+)[DDQ]˙(-) (DDQ = 2,3-dichloro-5,6-dicyanoquinonide) were measured at ambient and applied hydrostatic pressures up to 11.4 and 9.2 kbar, respectively. At ambient pressure [FeCp*2][HCBD] exhibits spin glass-like behavior with a freezing temperature, Tf, of 2.93 K from the peak in χ'(T) at 10 Hz, but magnetic ordering is not evident due to the lack of a remnant magnetization, bifurcation temperature, and hysteresis. Above 3.1 kbar, [FeCp*2][HCBD] magnetically orders as a metamagnet with an antiferromagnetic ground state with an ordering temperature, Tc, of 2.46 K determined from the Fisher specific heat, which increases linearly to 4.80 K at 11.4 kbar at a rate of 0.28 K kbar(-1). Upon application of pressure metamagnetic-like behavior with hysteresis indicative of a weak ferromagnet (canted antiferromagnet) was observed at and above 3.1 kbar, with a coercive field, Hcr, of 65 Oe, which increases exponentially to 795 Oe at 11.4 kbar. [FeCp*2]˙(+)[DDQ]˙(-) did not magnetically order above 2 K, and magnetic order was not observed up to 9.2 kbar. The pressure dependencies are reversible.