Mixed ground state in Fe-Ni Invar alloys

We investigate the ground state properties of Invar alloys via detailed study electronic structure Fe1−xNix (x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9) employing x-ray photoelectron spectroscopy (XPS). While all exhibit soft ferromagnetic behavior with Curie temperature much higher than room temperature, results for invar alloy, Fe0.6Ni0.4 anomalous behavior. Moreover, magneto-resistance alloy becomes highly negative while end members possess positive magneto-resistance. The core level spectra emergence a distinct new feature below 20 K other Fe-Ni no dependence down to 10 K. Interestingly, shallow (3s, 3p) Fe and Ni reveal stronger deviation at low temperatures compared deep levels (2s, 2p) indicating crystal field effect. It appears that there is large precipitation antiferromagnetic γ′ phase possessing magnetic moment (0.5μB) on within α phase. discovery magneto-resistance, magnetization unusual features in provide an evidence mixed alloys.