Temperature-induced mixed magnetic states in FeRh@FeO composite nanoparticles

Reducing the size of a material with a first-order magnetic phase transition to the nanoscale results in a significant change in its physical properties. An example of this behaviour is the FeRh alloy. According to magnetometry results, the nanoparticles of this alloy do not show a transition from the antiferromagnetic to the ferromagnetic state near room temperature. In this work we have measured the magnetic properties and the Mössbauer effect for FeRh@FeO composite nanoparticles at different temperatures. An analysis of the results allows us to conclude that superparamagnetic relaxations dominate the formation of the magnetic structure of the nanoparticles. For particle sizes near 10 nm, the antiferromagnetic state is possible near helium temperatures. Further heating contributes to the formation of superparamagnetic behaviour. •Magnetic phase transitions in FeRh nanoparticles have been revealed.•The role of magnetization relaxation in the formation of magnetic ordering is demonstrated.•The electronic structure near iron atoms is characterized.•The effect of iron oxide on the surface of FeRh particles on the magnetic properties has been studied.