Structural, magnetic, electric, dielectric, and thermodynamic properties of multiferroic GeV4S8

Abstract

The lacunar spinel GeV4S8 undergoes orbital and ferroelectric ordering at the Jahn-Teller transition around 30 K and exhibits antiferromagnetic order below about 14 K. In addition to this orbitally driven ferroelectricity, lacunar spinels are an interesting material class, as the vanadium ions form V4 clusters representing stable molecular entities with a common electron distribution and a well-defined level scheme of molecular states resulting in a unique spin state per V4 molecule. Here we report detailed x-ray, magnetic susceptibility, electrical resistivity, heat capacity, thermal expansion, and dielectric results to characterize the structural, electric, dielectric, magnetic, and thermodynamic properties of this interesting material, which also exhibits strong electronic correlations. From the magnetic susceptibility, we determine a negative Curie-Weiss temperature, indicative for antiferromagnetic exchange and a paramagnetic moment close to a spin S = 1 of the V4 molecular clusters. The low-temperature heat capacity provides experimental evidence for gapped magnon excitations. From the entropy release, we conclude about strong correlations between magnetic order and lattice distortions. In addition, the observed anomalies at the phase transitions also indicate strong coupling between structural and electronic degrees of freedom. Utilizing dielectric spectroscopy, we find the onset of significant dispersion effects at the polar Jahn-Teller transition. The dispersion becomes fully suppressed again with the onset of spin order. In addition, the temperature dependencies of dielectric constant and specific heat possibly indicate a sequential appearance of orbital and polar order.

arXiv comment15 pages, 9 figures

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Cited by in corpus (8)

• Rank-2 $U(1)$ spin liquid on the breathing pyrochlore lattice
• Polar and magnetic order in GaV4Se8
• Cooperative cluster-Jahn-Teller effect as a possible route to antiferroelectricity
• Lattice dynamics and electronic excitations in a large family of lacunar spinels with a breathing pyrochlore lattice structure
• Optical conductivity in multiferroic GaV${}_4$S${}_8$ and GeV${}_4$S${}_8$: Phonons and electronic transitions
• Terahertz Dielectric Analysis and Spin-Phonon Coupling in Multiferroic GeV${}_4$S${}_8$
• Excitations and relaxation dynamics in multiferroic GeV4S8 studied by THz and dielectric spectroscopy
• Optical, dielectric, and magnetoelectric properties of ferroelectric and antiferroelectric lacunar spinels