Low-temperature magneto-transport properties of nanostructured alloys with disordered magnetic subsystems

Abstract

This work investigates how nanostructuring and controlled disorder govern low-temperature magnetotransport in Fe–Cr–Ni–B alloys with a deliberately disordered magnetic subsystem. Bulk alloys of nominal composition Fe₇₃Cr₁₀Ni₇B₁₀ were prepared by arc melting, high-energy ball milling, and short-time annealing between 450 and 550 degrees Celsius. The resulting microstructures were characterized by X-ray diffraction with profile analysis, scanning and transmission electron microscopy, and magnetization measurements under zero-field-cooled and field-cooled protocols. Electrical resistivity, magnetoresistance, and Hall effect were measured from 2 to 300 kelvin in magnetic fields up to 14 tesla using four-probe and five-contact configurations. The alloys form nanocrystalline Fe-based solid solutions with characteristic crystallite sizes increasing from about 18 to 38 nanometres as the annealing temperature rises, while microstrain and porosity decrease. Magnetization data reveal glassy freezing and unsaturated hysteresis, confirming a frustrated, disordered magnetic subsystem. All samples show high resistivity at room temperature, around 185 to 230 microohm centimetres, with low residual resistivity ratios and a crossover of the low-temperature exponent from approximately 1.3 to 1.9 as structural disorder is reduced. At 5 kelvin and 14 tesla, a sizable negative magnetoresistance of roughly 7, 5, and 3 percent is observed for the three annealing states, accompanied by metallic, electron-like Hall response. Together, these results demonstrate a clear correlation between nanostructure, magnetic disorder, and magnetotransport, and show that modest changes in crystallite size and microstrain provide an efficient handle to tune spin-disorder scattering in disordered magnetic alloys.