Charge-stripe order, antiferromagnetism, and spin dynamics in the cuprate-analog nickelate La4Ni3O8

We report results of a muon spin rotation (mu SR) study of the cuprate-analog nickelate La4Ni3O8, which undergoes a transition at 105 K to a low-temperature phase with charge-stripe and antiferromagnetic (AFM) order on square planar NiO2 layers. Zero-field mu SR shows that the AFM transition is abrupt, commensurate, and has a quasi-two-dimensional character below similar to 25 K. Comparison of observed muon precession frequencies with Ni dipolar field calculations yields Ni moments less than or similar to 0.5 mu(B). Dynamic muon spin relaxation above 105 K suggests critical slowing of Ni spin fluctuations, but is inconsistent with corresponding La-139 NMR results. Critical slowing and an abrupt transition are also observed in the planar cuprate AFM La2CuO4+delta, where they are taken as 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 when applied to the nickelate.