Abstract
Chirality or the handedness of objects is of prime importance in life science, biology, chemistry, and physics. It is also a major symmetry ingredient in frustrated magnets revealing spin-spiral ground states. Vector-chiral phases, with the twist (either clock- or counter clock-wise) between neighboring spins being ordered, but with disorder with respect to the angles between adjacent spins, have been predicted almost five decades ago. Experimental proofs, however, are rare and controversial. Here, we provide experimental evidence for such a phase in LiCuVO4, a one-dimensional quantum magnet with competing ferromagnetic and antiferromagnetic interactions. The vector-chiral state is identified via a finite ferroelectric polarization arising at temperatures well above the multiferroic phase exhibiting long-range three-dimensional spin-spiral and polar order. On increasing temperatures, spin order becomes suppressed at TN, whereas chiral long-range order still exist, leaving a temperature window with chirality-driven ferroelectricity in the presence of an external magnetic field.
Highlights
In recent years, magnetic materials exhibiting spin spirals gained considerable attention owing to their helical or cycloidal spin configurations.[1]
In light of the mentioned ferroelectric (FE) polarization induced by chiral spin twists,[3–5,22] the most promising route seems to search for VC phases by identifying FE polarization at temperatures slightly above wellknown 3D-ordered spin-driven multiferroic phases.[13,25]
LiCuVO4 offers a rich variety of complex magnetic phases, like the possible appearance of a bond-nematic phase at low temperatures and high magnetic fields.[26–30]
Summary
Magnetic materials exhibiting spin spirals gained considerable attention owing to their helical or cycloidal spin configurations.[1]. There the chiral spin twist can induce spin-driven ferroelectricity[2] either via a spin-current mechanism[3] or via an inverse Dzyaloshinskii–Moriya interaction.[4,5]. This revitalized the large field of multiferroics,[6] being of great fundamental and technological importance.[7,8]. Either finite temperatures or quantum fluctuations can completely suppress the long-range spin order of a spiral, while leaving the chiral twist less affected, leading to a vector-chiral (VC) phase. In light of the mentioned ferroelectric (FE) polarization induced by chiral spin twists,[3–5,22] the most promising route seems to search for VC phases by identifying FE polarization at temperatures slightly above wellknown 3D-ordered spin-driven multiferroic phases.[13,25]. In light of the mentioned ferroelectric (FE) polarization induced by chiral spin twists,[3–5,22] the most promising route seems to search for VC phases by identifying FE polarization at temperatures slightly above wellknown 3D-ordered spin-driven multiferroic phases.[13,25] From a theoretical point of view, quantum spin-chain systems with ferromagnetic (FM) nearest neighbor (nn) and antiferromagnetic (AFM) next-nearest neighbor (nnn) exchange, for which the inverse spinel compound LiCuVO4 is a prime example, seem perfectly appropriate to detect the VC phase.[13]
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