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

A comprehensive study of the magnetic properties (magnetostriction, magnetic susceptibility, Curie temperature) andthermal 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 ofthe sample were used: along and across the tape (longitudinal and transverse samples). Measurements of magnetization and thermalexpansion were carried out in the temperature range 90 – 300 K in fields up to 6.5 kOe. To determine the change in the length ofthe sample under the influence of a magnetic field or in connection with a change in temperature, we used the method of wireconstantan strain gauges connected according to the DC bridge circuit. The sensitivity of the setup to the relative change in thelength of the sample was 8·10-7. The basis for determining the Curie temperature was the temperature dependence of the initialmagnetic susceptibility obtained by the induction method.It is shown that the linear magnetostriction constant and the Curie temperature decrease with increasing nickelconcentration. The nonlinear character of the Tc(x) dependence indicates an active participation of Ni atoms in the exchangeinteraction in alloys containing boron, in contrast to alloys with phosphorus. The volume (forced) magnetostriction was detectedand 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 notqualitatively change, the saturation magnetostriction increases with decreasing temperature in the range 300 – 100 K. Theindependence of the character of the curves ( ) ( ) s  l l T on x indicates that the predominance of the single-ion mechanism of theformation 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 coefficientmonotonically increases with increasing nickel concentration, which correlates with a decrease in volume magnetostriction