  Neodymium nickelates have attracted research interest due to their strongly
correlated behaviour and remarkable magnetic properties. More importantly,
superconductivity has recently been confirmed in thin-film samples of Sr-doped
NdNiO2, bringing the layered rare earth nickel oxides into the research
spotlight. In this report, we present results on a series of NdNiO2 analogues,
NdxPr4-xNi3O8 (x = 0.1, 0.25, 1, 2, and 4) obtained by topotactic reduction, in
which we observe systematic changes in the magnetic behaviour. As the Nd3+
content increases, the initially large spin-freezing region with magnetic
frustration becomes smaller and gradually shifts to low temperatures, while the
magnetic response gradually increases. The muon-spin spectroscopy measurements
on Nd4Ni3O8 show that this phenomenon is likely due to the enhancement of spin
fluctuations in NdxPr4-xNi3O8, which weakens the spin frustration behaviour for
high Nd3+ contents and at low temperatures. These spin fluctuations can be
caused by both Nd and Ni ions and could be one of the factors determining the
occurrence of possible superconductivity.
