Charge-stripe order, antiferromagnetism, and spin dynamics in the cuprate-analog nickelate La$_4$Ni$_3$O$_8$

TL;DR

This study uses muon spin rotation to investigate charge-stripe and antiferromagnetic order in La4Ni3O8, revealing an abrupt transition at 105 K with weak Ni moments and complex spin dynamics, contrasting with theoretical models.

Contribution

First muon spin rotation investigation of La4Ni3O8 revealing detailed magnetic order and spin dynamics, highlighting discrepancies with existing theoretical predictions.

Findings

Charge-stripe and AFM order appear at 105 K

Ni moments are estimated to be less than 0.5μB

Critical slowing of Ni spin fluctuations observed above transition

Abstract

We report a muon spin rotation ($\mu$SR) study of the cuprate-analog nickelate La$_4$Ni$_3$O$_8$, which undergoes a transition at 105 K to a low-temperature phase with charge-stripe and antiferromagnetic (AFM) order on square planar NiO$_2$ layers. Zero-field $\mu$SR shows that this transition is abrupt and that the AFM configuration is commensurate. Comparison of observed muon precession frequencies with Ni dipolar field calculations yields Ni moments $\lesssim 0.5\mu_B$. Dynamic muon spin relaxation above 105 K suggests critical slowing of Ni spin fluctuations, but is inconsistent with corresponding $^{139}$La NMR results. Critical slowing and an abrupt transition are also observed in the planar cuprate AFM La$_2$CuO$_{4+\delta}$, where they are evidence for weakly interplanar-coupled two-dimensional AFM spin fluctuations, but our $\mu$SR data do not agree quantitatively with theoretical predictions for this scenario.