Abstract
We present neutron scattering measurements on powder samples of the spinel FeSc2S4 that reveal a previously unobserved magnetic ordering transition occurring at 11.8(2)~K. Magnetic ordering occurs subsequent to a subtle cubic-to-tetragonal structural transition which distorts Fe coordinating sulfur tetrahedra lifting the orbital degeneracy. The application of 1~GPa hydrostatic pressure appears to destabilize this N\'eel state, reducing the transition temperature to 8.6(8)~K and redistributing magnetic spectral weight to higher energies. The relative magnitudes of ordered $\langle m \rangle^2\!=\!3.1(2)$ and fluctuating moments $\langle \delta m \rangle^2\!=\!13(1)$ show that the magnetically ordered ground state of FeSc2S4 is drastically renormalized and in proximity to criticality.
Highlights
In a quantum spin liquid, quantum fluctuations overcome the development of any long-range magnetic order resulting in a dynamic state that breaks no symmetries at T 1⁄4 0
At T 1⁄4 1.6 K, the peak intensity of the strongest magnetic Bragg peak at Q 1⁄4 0.6 Å−1 amounts to 20% of the strongest nuclear Bragg peak intensity at Q 1⁄4 1.69 Å−1. We argue that these Bragg peaks arise from a magnetic ordering transition that is enabled by a higher-temperature orbital ordering transition
We argue below that the finite magnetic correlation length is a result of exchange disorder built into the system at the higher-temperature orbital occupational ordering transition
Summary
In a quantum spin liquid, quantum fluctuations overcome the development of any long-range magnetic order resulting in a dynamic state that breaks no symmetries at T 1⁄4 0. The search for this precarious state of matter in a real material is a decade’s-old quest of condensed matter physics [1]. Frustrated magnetic materials are a focal point Their competing exchange interactions can produce an extensive degeneracy that promotes quantum fluctuations and precludes the development of a staggered magnetization [2]. Orbital degeneracy that influences the spin sector through spinorbit coupling and impacts exchange interactions can enhance spin fluctuations and suppress magnetic order [3]. Orbital degrees of freedom may even form a quantum fluid in the presence of a staggered magnetization [4,5,6], or both spins and orbital sector can form a combined spinorbital liquid state [7,8]
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