Magnetic resonance of zinc- and copper-ferrite ionic magnetic fluids: temperature effects

Abstract Magnetic resonance was used to investigate ionic magnetic fluids based on ZnFe 2 O 4 and CuFe 2 O 4 nanoparticles. Temperature and angular variation measurements were performed with field-frozen samples, using an X-band spectrometer. The resonance line shape analysis indicates the presence of four components, irrespective of the temperature and sample orientation. Intermediate values of the anisotropy field were associated to dimers, while low and high values of the anisotropy field were associated to large- and small-sized monomers, respectively. The temperature dependence of the resonance field associated to each resonance line allowed quantitative investigation of the surface anisotropy component. Positive as well as negative surface anisotropy components, as obtained from the temperature dependence of the resonance field, are reported.