dc.description.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. |
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