Multiferroic spin-superfluid and spin-supersolid phases in MnCr2S4

Abstract

Spin supersolids and spin superfluids reveal complex canted spin structures with independent order of longitudinal and transverse spin components. This work addresses the question whether these exotic phases can exhibit spin-driven ferroelectricity. Here we report the results of dielectric and pyrocurrent measurements of MnCr2S4 as function of temperature and magnetic field up to 60 T. This sulfide chromium spinel exhibits a Yafet-Kittel type canted spin structure at low temperatures. As function of external magnetic field, the manganese spins undergo a sequence of ordering patterns of the transverse and longitudinal spin components, which can be mapped onto phases as predicted by lattice-gas models including solid, liquid, super-fluid, and supersolid phases. By detailed dielectric and pyrocurrent measurements, we document a zoo of multiferroic phases with sizable ferroelectric polarization strongly varying from phase to phase. Using latticegas terminology, the title compound reveals multiferroic spin-superfluid and spin-supersolid phases, while the antiferromagnetic solid is paraelectric.

Element-specific field-induced spin reorientation and an unusual tetracritical point in MnCr2S4

“…Our element-selective XMCD results complemented by this MCE data provide compelling evidence for the proposed noncollinear (collinear) magnetic structures in the phases II and III (IV ). This is in line with a recent report suggesting a spin current or inverse Dzyaloshinskii-Moriya mechanism to be responsible for the multiferroic properties observed in the phases II and III [16]. Furthermore, our MCE results indicate the importance of the adiabatic temperature changes for mapping the H-T phase diagram from pulsed-field experiments (see Sec.…”

“…Remarkably, our observations signal the presence of a tetracritical point in the phase diagram, which was already suggested from the phase diagram determined from pyrocurrent measurements [16]. The transition lines that cross at the TP presumably belong to second-order transitions, because of the absence of any divergent and/or hysteretic behavior in the experimental results.…”

“…In addition, from a quantum lattice-gas model, the YK state and the intermediate phase, which is located between the YK and plateau phases, were suggested to be spin-superfluid and spin-supersolid states, respectively [13][14][15]. Very recently, multiferroicity has been reported in the YK and intermediate phases of MnCr 2 S 4 [16,17]. However, a detailed understanding of the magnetic structure in the field-induced phases in MnCr 2 S 4 is still missing.…”

Localized-delocalized crossover of spin-carriers and magnetization reversal in Co$_{2}$VO$_{4}$

“…The AB 2 X 4 -type spinel compounds, with tetrahedral A-site and octahedral B-site, have been an anchoring point for some of the earliest work on magnetism that led to the seminal Néel [1] and the Yafet-Kittel models [2]. The spinel (and the inverse-spinel) compounds display a complex interplay among lattice, spin, charge, and orbital degrees of freedom [3], where novel phenomena emerge [4,5]. Indeed, interest in these systems persists as they exhibit exotic magnetic phenomena, such as multiferroic effects and the spin liquid state that result from spin-orbit coupling and geometric frustration associated with the pyrochlore sub-lattice of the B-site [6,7].…”

Mixed-spin system with supersolid phases: magnetocaloric effect and thermal properties

“…An appropriate ground for searching various supersolid phases are quantum spin systems [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34]. Recently it has been shown experimentally that mixed-spin systems, composed of two kinds of spin, display various supersolid phases in their ground state phase diagrams [35,36]. Mixed-spin systems are a special class of spin models, where their universality class is completely different from uniform spin models [37,38,39,40,41,42,43,44].…”