Field-induced magnetic phases and electric polarization in LiNiPO4

TL;DR

This study investigates the magnetic phase transitions and electric polarization mechanisms in LiNiPO4 under magnetic fields along the c-axis, revealing the relationship between magnetic order and the magneto-electric effect.

Contribution

It provides the first detailed neutron diffraction analysis of the (H,T) phase diagram of LiNiPO4, linking magnetic phases to electric polarization behavior.

Findings

C magnetic order is essential for the magneto-electric effect.

High magnetic fields induce a transition from commensurate to incommensurate magnetic order.

Electric polarization arises from a field-induced reduction in magneto-elastic energy.

Abstract

Neutron diffraction is used to probe the (H,T) phase diagram of magneto-electric (ME) LiNiPO4 for magnetic fields along the c-axis. At zero field the Ni spins order in two antiferromagnetic phases. One has commensurate (C) structures and general ordering vectors (0,0,0), the other one is incommensurate (IC) with ordering vector (0,q,0). At low temperatures the C order collapses above 12 Tesla and adopts an IC structure with modulation vector parallel to (0,q,0). We show that C order is required for the ME effect and establish how electric polarization results from a field-induced reduction of the total magneto-elastic energy.