Abstract:
In the present work the detailed study of magnetic phase transition and critical point behavior,
magneto stricti on and temperature dependence of resistivity of the amorphous alloys Coso_xFexBloSilO
and Ni sO-xFe xB20with x= 2,4,6,8 and x= 20,30,40,50 has been carried out respectively.
Metallic glass ribbons of Co-Fe-B-Si and Ni-Fe-B alloys are prepared by melt spinning technique.
A review of theory of magnetic phase transition and critical point behavior of some iron - nickel
based amorphous materials is presented. The magnetic phase transition and critical phenomena of
COso-xFexBIOSiIOand Niso_xFexB2oalloys are investigated by using the experimental values of
magnetization as a function of magnetic field and temperature. Magnetization measurements on the
Coso-xFexBIOSiiOand Niso_xFexB2oalloy samples were carried out in the temperature range 301 to
716 K and in magnetic fields up to 4 Koe_ The critical exponents are deduced from magnetization
measurements. The ferromagnetic transition temperature (Te), and critical exponents (~, y and 8)
have been determined by using the magnetic state equations in the critical region_ The values of~,
y and 8 are discussed and compare~ with the results of various theoretical models. The data are
fitted to a magnetic equation of state characteristics of a second - order phase transition over a
rather wide range of temperature both above and below Te.
Magnetostriction of the above samples prepared by melt spinning technique have been measured
by resistance strain gauge technique at room temperature as a function of field and from liquid
nitrogen temperature to room temperature at constant malsnetic field. The linear saturation
magnetostriction of the amorphous Coso-xFexBIOSiiOwith x= 2,4,6,8 ribbons have been calculated
by rotating the magnetization vector from perpendicular position to parallel position of the
magnetization direction with respect to the direction of strain measurement. It is considered that the
direction of the field and the direction of magnetization practically coincide at maximum field. The
d•irection of the strain measurement is taken on the direction of the bonded strain gauge. The
saturation magnetostriction decreases as Co concentration increases and Fe-concentration
decreases. Here the observed magnetostriction has been calculated in terms of the theory explained
in chapter 5.The results are described in terms of domain motion and domain rotation that are
spontaneously strained.
