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

Magnetic resonance was used to investigate ionic magnetic fluids based on Z nFe2O4 and CuFe2O4 nanoparticles. Temperature and angular variation measure ments were performed with field-frozen samples, using an X-band spectromete r. The resonance line shape analysis indicates the presence of four compone nts, irrespective of the temperature and sample orientation. Intermediate v alues of the anisotropy field were associated to dimers, while low and high values of the anisotropy field were associated to large- and small-sized m onomers, respectively. The temperature dependence of the resonance field as sociated to each resonance line allowed quantitative investigation of the s urface anisotropy component. Positive as well as negative surface. anisotro py components, as obtained from the temperature dependence of the resonance field, are reported. (C) 2001 Elsevier Science B.V. All rights reserved.