Probing magnetic order in LiMPO4, M = Ni, Co, Fe and lithium diffusion in LixFePO4

TL;DR

This study investigates magnetic ordering in LiMPO4 compounds and lithium diffusion in LixFePO4 using muon spin relaxation, revealing distinct magnetic behaviors and quantifying lithium diffusion parameters at various compositions and temperatures.

Contribution

It provides new insights into magnetic phase behavior in LiMPO4 and quantifies lithium diffusion characteristics in LixFePO4, combining magnetic and diffusion analyses.

Findings

LiNiPO4 exhibits different muon decay asymmetries in magnetic phases.

LiCoPO4 shows decreasing interlayer correlation near Neel temperature.

LixFePO4 demonstrates lithium diffusion with an activation barrier of ~100 meV.

Abstract

Muon spin relaxation measurements are reported on three members of the LixMPO4 series. The magnetic properties of stoichiometric samples with M = Ni, Co, Fe, were investigated at low-temperature. In LiNiPO4 we observe different forms of the muon decay asymmetry in the commensurate and incommensurate antiferromagnetic phases, accompanied by a change in the temperature dependence of the muon oscillation frequency. In LiCoPO4 the form of the muon decay asymmetry indicates that the correlation between layers decreases as the Neel temperature is approached from below. LiFePO4 shows more conventional behaviour, typical for an antiferromagnet. Measurements on LixFePO4 with x = 0.8, 0.9, and 1 show evidence for lithium diffusion below ~250 K and muon diffusion dominating the form of the relaxation at higher temperature. The thermally activated form of the observed hopping rate suggests an activation barrier for lithium diffusion of ~ 100 meV and a diffusion constant of D_Li ~ 10^-10 - 10^-9 cm2/s at room temperature.