Temperature dependence of FMR and magnetization in nanocrystalline zinc ferrite thin films

Abstract

Single phase nano-crystalline zinc ferrite thin films were deposited by RF-magnetron sputtering on quartz substrate at room temperature (RT) in pure Argon environment and annealed (in air) at different temperatures. Temperature dependence of magnetization was studied on these films using both VSM and by observing FMR (in X band). Value of exchange stiffness constant (D) was obtained by fitting Bloch’s law to the low temperature magnetization data. The value of D decreased monotonously with the annealing temperature (TA) of the samples. A film annealed at TA = 523 K, exhibited the highest magnetization value. The FMR line width of the films decreased with increase in measurement temperature. At RT (∼293 K), the lowest value of line width (ΔH) was 15 kA/m and 13 kA/m in parallel and perpendicular configuration respectively for the sample annealed at TA = 623 K.

Effect of substrate temperature on magnetic properties of MnFe2O4 thin films

“…The value of 4πM eff is equal to the saturation magnetization after subtracting H k , where H k is the uniaxial anisotropy field. 18,19 The Lande's g-factor can be obtained from gyromagnetic ratio, 20 which in turn is obtained from solving Eq. (1) and (2) and was observed to vary between ∼ 2.1 to ∼ 2.3.…”

“…These values are fitted with Bloch's law (Eq. (3)) 19 where M S (0) is the saturation magnetization at zero K and B is the coefficient of T 3/2 . The Bloch's law is derived on the assumption that the reduction in the magnetic moment of the material with rising temperature is on account of excitation of spin waves.…”

“…The magnetization in nanocrystalline ferrite thin films normally is found to be different from bulk materials and is believed to be due to a changed cation distribution. 19,23,24 However, in case of the MnFe 2 O 4 films, any change in occupancy of Fe 3+ and Mn 2+ on A and B sites does not change the net magnetization. In spite of this, we observe an overall increase in the magnetization with increase in T S which is due to an increase in grain size.…”

Effect of thickness on magnetic and microwave properties of RF-sputtered Zn-ferrite thin films

“…Such a non saturation is a common occurrence in nano-crystalline ferrite thin films and powders. 8,[10][11][12][13][14] The spontaneous magnetization (4πM S ) values were calculated for our films by extrapolating the higher field part of M-H curves (between 30 kOe to 50 kOe) to zero magnetic field (shown in Fig.2a for t=360 nm film) and are reported in the paper. 10,11 Fig .2b shows the variation of magnetization (4πM S ) as a function of thickness for ASD and a few annealed films.…”

“…Such an asymmetry in FMR spectra have been reported to arise due to the surface inhomogeneity in the RF-sputtered ZnFe 2 O 4 thin films. 14 The values of effective magnetization (4πM eff ) and Lande's spectroscopy splitting factor (g) were calculated from the in-plane and perpendicular FMR field position using Kittel's equations. 16 From the analysis of FMR spectra, it is seen that the effective magnetization follows the same trend observed in the case of 4πM S as a function of thickness and T A .…”