Abstract
Ni3V2O8 is an archetypical multiferroic material with a kagome staircase structure of S = 1 (Ni2+) spins whose complex interplay between spin ordering and ferroelectricity has been studied for more than a decade. Here, we report a new kagome staircase compound PbCu3TeO7 with Cu2+ (S = 1/2) spins that exhibits two Néel temperatures at TN1 = 36 K and TN2 = 24 K, and a magnetic field (H)-induced electric polarization (P) below TN2. Pyroelectric and magnetoelectric current measurements in magnetic fields up to 60 T reveal that for H||c of ~ 8.3 T, a spin-flop transition induces a transverse P||a with a magnitude of 15 µC/m2 below TN2. Furthermore, for a parallel configuration with P//H//a, two spin-flop transitions occur, the first at ~ 16 T with P//a of 14 µC/m2, and the second at ~ 38 T, where P disappears. Monte Carlo simulations based on 12 major exchange interactions uncover that a sinusoidal amplitude modulation of the spins occurs along the b-axis below TN1 and an incommensurate, proper screw-type spin order occurs in the ac-plane below TN2. The simulation results show that P//a under H//c stems from a spin-flop transition facilitating an ab-plane-type spiral order, while the two successive spin-flop transitions for H//a result in spiral spin orders in the ab- and bc-planes. Based on the experimental and theoretical results, we establish field-induced magnetic and electric phase diagrams for the two H directions, demonstrating that the distorted kagome staircase structure with competing intra–interlayer interactions and lifted frustration creates a plethora of different noncollinear spin textures of S = 1/2 spins that in turn induce electric polarization.
Highlights
Research activities on multiferroics and magnetoelectric (ME) materials have resumed since early 2000s because of the fundamental interests in the physics of strong coupling between spin and lattice degrees of freedom as well as the application potential for numerous low-power electronic devices.[1,2,3,4,5] In particular, magnetic ferroelectrics, in which ferroelectric polarization (P) is induced by spin order, have drawn lots of attention due to the intriguing complexity of the spin textures and magnetoelectric coupling mechanisms, as well as the ability to control 100% of the electric polarization with magnetic ordering
One route to creating ferroelectricity is via competing magnetic interactions that induce complex nontrivial spin orders
Ferroelectricity observed in quasi-onedimensional spin chain compounds MnWO4,6 Ca3Co1.04Mn0.96O6,7 and Lu2CoMnO68 can be explained by such complex spin orders induced by the competing nearest and next-nearest neighbor exchange interactions
Summary
Research activities on multiferroics and magnetoelectric (ME) materials have resumed since early 2000s because of the fundamental interests in the physics of strong coupling between spin and lattice degrees of freedom as well as the application potential for numerous low-power electronic devices.[1,2,3,4,5] In particular, magnetic ferroelectrics, in which ferroelectric polarization (P) is induced by spin order, have drawn lots of attention due to the intriguing complexity of the spin textures and magnetoelectric coupling mechanisms, as well as the ability to control 100% of the electric polarization with magnetic ordering. Ferroelectricity observed in quasi-onedimensional spin chain compounds MnWO4,6 Ca3Co1.04Mn0.96O6,7 and Lu2CoMnO68 can be explained by such complex spin orders induced by the competing nearest and next-nearest neighbor exchange interactions. Spontaneous P can be induced by the IDM mechanism.[22,23,24] recently known multiferroic compound KCu3As2O7(OD)[3] has a monoclinically distorted kagome structure, which allows long-range spin order with a cycloidal configuration.[37,38] to our knowledge, no ME or multiferroic behaviors have been found to date in the staircase kagome spin structure with S = 1/2 Cu2+ ions, which could open a new route to find exotic magnetic and multiferroic phenomena due to its unique opportunity of having quantum fluctuation, geometric spin frustration, and competing nearest- and nextnearest spin interaction all in one spin network. Our calculations suggest that the Pa generated by μ0Hc > 8.3 T and 16 T < μ0Ha < 38 T stems from a cycloid spin phase rotating in the ab-plane
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