Magnetization dynamics in rare earth Gd3+ doped Mn0.5Zn0.5Fe2O4 magnetic fluid: Electron spin resonance study

• Published in: Journal of magnetic resonance (1997) 2012-12, Vol.225, p.46-51
• Main Authors: Parekh, Kinnari, Upadhyay, R.V.
• Format: Article
• Language: English
• Subjects: Electron paramagnetic resonance; Electron spin resonance; ESR; Ferrite; Freezing; Magnetic fluid; Magnetic fluids; Magnetic resonance; Magnetization; Rare earth metals; Spectra; Surface spin glass
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2012.10.001

[Display omitted] ► Zero field cooled spectra exhibit an isotropic resonance field shifts below 50K. ► Field cooled spectra show angle dependent hysteresis below 50K. ► Results point to the presence of surface spin glass structure at low temperature. ► Dc-susceptibility results show the presence of two different energy barriers. The electron spin resonance (ESR) technique has been applied to study the spin dynamics in broad temperature range for rare earth doped Mn0.5Zn0.5Fe1.9Gd0.1O4 (MZG5) magnetic fluid. Zero field cooled (ZFC) ESR spectra of MZG5 fluid exhibit an isotropic shift in the resonance field below 40K, while the field cooled (FC) ESR spectra show a deviation from sin2θ behavior and an angle dependent hysteresis, this unambiguously points to the dominating unidirectional freezing of surface spins below 40K. Above 60K, the resonance field exhibits sin2θ behavior, indicating the uniaxial anisotropy contribution of core spin. This indicates that surface spin freezing temperature is around 40K. The presence of surface spin freezing and the coupling between core and surface spins are further supported by cycle dependent FC ESR spectra measured at 20K, which show the systematic increase in resonance field (Hres) and intensity. The double peak behavior of blocking temperature distribution retrieved from ZFC-FC magnetization measurement is an additional corroboration of the existence of surface spin glass like layer.