Abstract
The nature of the magnetic ground state of the spin-frustrated molecular magnet {Mo72Fe30} is studied using polarized neutron scattering and specific heat methods. The magnetic scattering cross section up to 2.30 Å−1 has been determined by means of diffuse neutron scattering with xyz polarization analysis at temperatures from 1.5 to 100 K. The spin correlations observed at 1.5 K agree well with the simulation based on the three-sublattice spin configuration model for {Mo72Fe30}. The specific heat of {Mo72Fe30} has been measured from 60 mK to 15 K under zero external magnetic field. The energy gaps, 0.09(1) and 0.64(1) meV, identified by the Schottky-type anomalies in the specific heat data are in reasonable agreement with the low-lying magnetic excitations predicted by the quantum rotational band model for the three-sublattice spin configuration model. Therefore, our experimental study provides strong support that the three-sublattice spin configuration model is a good approach to the magnetic ground state of {Mo72Fe30}.
Highlights
Hilbert space for this large spin system is 630
The energy gaps that we found in the specific heat data basically reflect the low-lying magnetic excitations in {Mo72Fe30}
The spin correlations collected at 1.5 K agree well with the simulation of the Fourier transform of the spin pair-correlation function using the three-sublattice spin configuration model
Summary
Hilbert space for this large spin system is 630. Despite this unsolvable difficulty at present, an approximate, diagonalizable effective Hamiltonian was adopted to explain the major lowtemperature properties of {Mo72Fe30} [11]. The classical version of this effective Hamiltonian represents a frustrated ground state spin configuration called the ‘three-sublattice’ model, where the 30 spins can be divided into three sublattices and the sublattices are characterized by three coplanar unit vectors with an angular spacing of 120◦ [12] This model successfully predicts the magnetic field dependence of the magnetic moment and the susceptibility of {Mo72Fe30} [10, 12]. In our zero-field specific heat data, Schottky anomalies with their unique shape for two-level systems are observed and serve as a clear signature to identify the energy gaps Using this complementary method for INS, our work gives additional strong support to the existing theoretical descriptions of low-lying magnetic excitations in {Mo72Fe30}
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