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^IIICp*₂]˙⁺[HCBD]˙⁻ (Cp* = pentamethylcyclopentadienide; HCBD = hexacyanobutadienide, C₄(CN)₆) and [Fe^IIICp*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, T_f, 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, T_c, 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, H_cr, 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.