Magnetic field induced ferroelectric transition of quasi one-dimensional frustrated quantum spin chain system Rb2Cu2Mo3O12

Abstract

Magnetic and dielectric properties have been studied for quasi one-dimensional spin 1/2 systems which are formed of edge-sharing CuO 4 square planes called CuO 2 ribbon chains. Due to the geometrical characteristic of the crystal structure of these systems, the nearest-neighbor exchange interaction J 1 between spins is relatively weak and often ferromagnetic, and the second neighbor interaction J 2 is antiferromagnetic. Under these situations, the helical ordering is often realized. Actually, LiVCuO 4 with the CuO 2 ribbon chains has the helical magnetic structure. For LiVCuO 4, we found that ferroelectric transition takes place simultaneously with a magnetic transition at T N =2.4 K (multiferroic) [1] as theoretically discussed in ref. 2. We have also found that PbCuSO 4 (OH) 2 with the CuO 2 ribbon chains has the helical magnetic structure and multiferroic behavior [3,4]. The quantum spin system can be considered as a new kind of multiferroics which may provide different aspects of physics from classical spin systems consisting of Fe 3+ and Mn 3+ with S > 1. Here, magnetic and dielectric properties of Rb 2 Cu 2 Mo 3 O 12 with CuO 2 ribbon chains are presented. The system does not exhibit a magnetic transition owing to quantum fluctuation and low dimensionality of crystal structure. We have observed anomalous increase of dielectric constant ε with decreasing T below ~50 K, which is originated from growing a short range ordering of a helical magnetic structure. For an external magnetic field H > 0.1 T, a peak structure is observed in the ε-T curve of Rb 2 Cu 2 Mo 3 O 12 at T c~8 K and the ferroelectric polarization has been observed below T c. However, the temperature dependence of magnetic susceptibility and specific heat do not have anomaly at T c in the magnetic field. These results indicate that the ferroelectric transition is found to be induced by applying field without magnetic transition. Then, these results strongly suggest that the magnetic field induced ferroelectric transition is a new type ferroelectric transition triggered by the magnetism of frustrated quantum spin systems.

Vector-spin-chirality order in a dimerized frustrated spin-12chain

“…(ii) The other is an even-parity dimer state realized with large enough easyplane magnetic anisotropy. Furthermore, recent experiments have shown that the applied magnetic field in a range of 0.1-2.0 T induces a ferroelectric polarization in the absence of a magnetic spiral LRO without closing the spin gap 29 , possibly realizing the genuine spingapped vector-spin-chirality ordered state. Such vectorchiral ordered state can be realized under a weak Zeeman field 30,31 .…”

Magnetoelectric coupling without long-range magnetic order in the spin- 12 multiferroic Rb2Cu2Mo3OReynolds1, Mannig2, Luetkens3 et al. 2019Phys. Rev. B13040View full textAdd to dashboardCite

“…A common feature of these models is that a bulk electric polarization may emerge when interacting spins display a long-range ordered arrangement that breaks spatial inversion symmetry. Recently, the highly frustrated quantum spin system Rb 2 Cu 2 Mo 3 O 12 (RCMO) has been reported to display magnetic-field tunable ferroelectricity below ∼8 K, yet remarkably there is no evidence from bulk measurements for a concomitant transition denoting the onset of magnetic longrange order [11]. The system thus poses an enticing question: In the seeming absence of long-range magnetism, what is the physical origin of the magnetically tunable ferroelectricity?…”

“…1(a), the system has a monoclinic crystal structure with S = 1/2 Cu 2+ ions forming a quasi-one-dimensional ribbon chain network along the crystal b axis. Up to now single-crystal samples have not been successfully synthesized, and experimental studies of this system are performed on powder samples [11][12][13][14][15]. Early temperature * jonathan.white@psi.ch (T )-dependent magnetic susceptibility data evidenced RCMO to host strongly frustrated magnetic interactions that could be modelled according to a dominant nearest-neighbor ferromagnetic (FM) and next-nearest-neighbor antiferromagnetic (AFM) exchange interactions with a ratio J FM /J AFM ∼ −2.7 [13].…”

Emergent spin-1 Haldane gap and ferroelectricity in a frustrated spin- 12 ladder

“…In fact, the ferroelectricity associated with the vector spin chirality order may appear robustly in the vectorchiral Haldane dimer phase without the long-range spiral magnetism, if the spin gap is enhanced [23] so that it dominates over the interchain interactions. Indeed, Rb 2 Cu 2 Mo 3 O 12 provides a unique example of a fieldinduced ferroelectricity hosted by a nonmagnetic ground state with a spin gap [16,17]. In this Letter, we report arXiv:1803.07081v1 [cond-mat.str-el] 19 Mar 2018 combined experimental and theoretical evidence that in the quasi-1D cuprate Rb 2 Cu 2 Mo 3 O 12 , a Haldane-gap ground state formed by emergent spin-1 pairs of S = 1/2 Cu spins ( Fig.…”

“…with the g-factor g = 2. 16 [26] and the applied magnetic field B, where S σ, stands for an S = 1/2 spin at the site in the chain of edge-shared CuO 6 octahedra ( Fig. 1(e)) labeled by the index σ = ±.…”