Magnetic properties and heat expansion of a binary Fe-Ni amorphous alloys

Abstract

A comprehensive study of the magnetic properties (magnetostriction, magnetic susceptibility, Curie temperature) and
thermal expansion of amorphous alloys of the (Fe1-xNix)78Si9B13 system of five compositions was carried out.
The samples were cut from a strip 30 μm thick and had a rectangular shape. Two variants of orientation of the long side of
the sample were used: along and across the tape (longitudinal and transverse samples). Measurements of magnetization and thermal
expansion were carried out in the temperature range 90 – 300 K in fields up to 6.5 kOe. To determine the change in the length of
the sample under the influence of a magnetic field or in connection with a change in temperature, we used the method of wire
constantan strain gauges connected according to the DC bridge circuit. The sensitivity of the setup to the relative change in the
length of the sample was 8·10-7. The basis for determining the Curie temperature was the temperature dependence of the initial
magnetic susceptibility obtained by the induction method.
It is shown that the linear magnetostriction constant and the Curie temperature decrease with increasing nickel
concentration. The nonlinear character of the Tc(x) dependence indicates an active participation of Ni atoms in the exchange
interaction in alloys containing boron, in contrast to alloys with phosphorus. The volume (forced) magnetostriction was detected
and estimated from the linear portions of the curves  l l (H) in fields above the saturation field. Bulk magnetostriction, like linear,
is positive and also decreases with increasing nickel content in the alloy.
Measurements of the dependence  l l (H) at different temperatures showed that the character of the curves does not
qualitatively change, the saturation magnetostriction increases with decreasing temperature in the range 300 – 100 K. The
independence of the character of the curves ( ) ( ) s  l l T on x indicates that the predominance of the single-ion mechanism of the
formation of magnetostriction in Ni-substituted iron-based alloys of the studied compositions is preserved.
Thermal expansion curves recorded in the range 90 – 300 K do not show anomalies, the linear expansion coefficient
monotonically increases with increasing nickel concentration, which correlates with a decrease in volume magnetostriction