Anomalies in the electronic, magnetic and thermal behavior near the Invar compositions of Fe-Ni alloys

TL;DR

This study investigates the structural, magnetic, and thermal anomalies in Fe-Ni alloys near Invar compositions, revealing phase structures, thermal expansion behavior, and magnetic interactions through various advanced characterization techniques.

Contribution

It provides new insights into the phase structures, thermal expansion coefficients, and magnetic interactions of Fe-Ni alloys near Invar compositions using synchrotron XRD, SQUID magnetometry, and XPS.

Findings

Invar composition (x=0.36) shows lowest CTE and single-phase fcc structure.

Mixed phase alloy (x=0.32) contains both bcc and fcc structures.

Magnetization decreases with cooling due to antiferromagnetic interactions.

Abstract

The structural and magnetic properties of Fe$_{1-x}$Ni$_x$~($x$ = 0.32, 0.36, 0.40, 0.50) alloys have been investigated using synchrotron based x-ray diffraction (XRD) technique with x-rays of wavelength 0.63658 \AA\ down to 50 K temperature, magnetic measurement using superconducting quantum interference device (SQUID) magnetometer and high resolution x-ray photoelectron spectroscopy (XPS) with monochromatic AlK$_\alpha$ radiation. The XRD studies suggest a single phase with fcc structure for $x$ = 0.36, 0.40, and 0.50 ~alloys and a mixed phase for $x$ = 0.32 alloy containing both bcc and fcc structures. The lattice parameter of the alloys exhibits a linear dependence on temperature giving rise to a temperature independent coefficient of thermal expansion (CTE). The lowest CTE is observed for $x$ = 0.36 Invar alloy as expected while $x$ = 0.50 alloy exhibits the highest CTE among the alloys studied. The CTE of the fcc component of mixed phase alloy is close to that of Invar alloy. The temperature dependence of magnetization of the alloys down to 2 K reveals an overall antiferromagnetic interactions within the ferromagnetic phase causing the magnetization decreasing with cooling. The field cooled and zero field cooled data show larger differences for the Invar compositions; this is also manifested in the magnetic hysteresis data at 2 K and 300 K.