Magnetic field-induced ferroelectricity in S = 1/2 kagome staircase compound PbCu 3 TeO 7

Ni 3 V 2 O 8 is an archetypical multiferroic material with a kagome staircase structure of S = 1 (Ni 2+ ) 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 PbCu 3 TeO 7 with Cu 2+ ( S = 1/2) spins that exhibits two Néel temperatures at T N1 = 36 K and T N2 = 24 K, and a magnetic field ( H )-induced electric polarization ( P ) below T N2 . 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/m 2 below T N2 . 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/m 2 , 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 T N1 and an incommensurate, proper screw-type spin order occurs in the ac -plane below T N2 . 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.