Low temperature specific heat of the molecular cluster Fe$_{8}$: contribution of the local field

TL;DR

This study investigates the low temperature specific heat of Fe8 molecular clusters, revealing the effects of local hyperfine and dipolar fields on ground state splitting and superparamagnetic behavior.

Contribution

It provides new insights into the role of local fields in the low temperature thermodynamic properties of Fe8, supported by specific heat and ac-susceptibility measurements.

Findings

Observation of superparamagnetic blocking below 1.3 K

Identification of excess specific heat due to ground state splitting

Confirmation of crystal field parameters through Schottky analysis

Abstract

We present low temperature specific heat and ac-susceptibility measurements on Fe$_{8}$ powdered sample. Below 1.3 K, superparamagnetic blocking effects as well as an excess specific heat contribution are evident. The latter is attributed to a splitting of the ground state doublet in an inhomogeneous local field of hyperfine and dipolar origin. The local field contributions are evident in the resonances observed in the field dependent ac-susceptibility and specific heat below 0.5 K. The low temperature Schottky contribution allowed us to check the crystal field parameters of effective spin Hamiltonians, recently proposed to simulate EPR and inelastic neutron scattering experiments.