Temperature dependance of magnetization and induced magnetic anisotropy of some Fe, Co and Ni-based amorphous ribbons

Abstract

Ferromagnetic amorphous ribbons of Fe-Si-B, Ni-Fe-B and Co-Fe-B-Si series have been prepared by rapid quenching technique and the amorphousity of the samples has been confirmed by X-ray diffraction technique. TIle kinetics of glass fonnation and crystallization as affected by a slight change in composition is studied by differential thennal analysis (DTA). It is observed that the thermodynamics of the amorphous ribbons in respect of tbe fonnation of glassy state and its stability is affected by the complexity of the composition. The magnetic ordering of Fe-based, Ni-based and Cobased amorphous ribbons is studied by measuring AC. and D.C. magnetization as functions of temperature. D.C. measurements are made by using a vibrating sample magnetometer and AC. initial permeability is measured, using a fumace in which the heating wire is wound in accordance with the bifiller technique. Coercivity, remanence, saturation magnetization and maximum permeability have been detennined as static magnetic propelties for Fe-based, Ni-based and Cobased specimens from the hysteresis loops obtained by Ballistic method: TIle dynamic characteristic such as the real and imaginary components of the complex penneability in AC. conditions have been measured as a function of the instantaneous value of a sine wave core current density by means of an adapted LCR bridge method. Initial penneability, frequency depeudence of complex penneability and relative quality factor have been measured in the frequency range O.5KHz to 13MHz for all the different compositions and for annealing effect of initial penneability. TIle measurements of saturation specific magnetization of Fe-based, Ni-based and Co-based amorphous ribbons have been measured by v.S.M. We h!ve correlated') the behaviour of magnetic moment in amorphous alloys containing 3d transition metals ' on the basis of rigid band model, assuming that the metalloid atoms contribute some of their S electrons and P electrons to fill the d band of the transition metal. TIJis accounts for the reduction of magnetization of all the amorphous ribbons with increasing metalloid content. The temperature dependence of magnetization, of amorphous system decreases faster with increasing temperature as compared to crystalline' materials. According to the mean field approximation, reduced magnetization versus reduced temperature graphs for different Fe-based, Ni-based and Co-based amorphous ribbons leads to fluctuation in the exchange interaction giving lise to a stmctural disorder. Induced magnetic anisotropy of amOlllhous ribbons having Fe-based, Ni-based and Co-based system have been measured for temperature and field dependence using torque magnetometer with proportional integrating differentiating compensation. TIle results of compositional dependence of initial permeability, coercive force and induced anisotropy are found to be mutually consistent for all the samples. TIle OI;gin the wliaxial anisotropy in these amorphous materials is assumed to be the stres~induced during the preparation. TIle temperature dependence of uniaxial anisotropy is caused by stress, relieving and decreases with the increase of temperature. 'nle corresponding curves of In[ ~)~~] versus In[ ;)~~] in amorphous ribbons with Fe-based, Ni-based and Co-based system follow straight lines arising from the disorder caused by randomly oriented easy axes. TIle values of the mqJonents arc different for the different samples. All amorphous ribbons have been investigated using Mossbauer spectroscopy. TIle Mossbauer measurements were perfonned with a conventional constant acceleration spectrometer at room temperature in transmission geometry, using "Co in a rhodium matrix. TIle velocity scale of a thin "Fe sample and the isomer shifts are given relative to the centroid of the spectrum. TIle isomer shifts of Fe-atoms in all the Fe, Ni and Co-based samples behave as tl;valent ions. TIle spectrum for the as prepared samples consists of six lines which are broadened as com~red with the Mossbauer spectrum of a pure '''Fe sample in the form of a thin foil. The curve for the experimental spectrum is obtained by using the best fit of the distribution of hyperfine fields. TIle consistency between the average magnetization measured by V.S.M. and the magnetic moment of the Fe-atom as estimated from the hyperfine field distribution confinns the collinearity of the magnetic ordering of the sample.