Resistance anomaly near phase transition in confined ferromagnetic nanowires

In this paper we report the study of the resistance anomaly close to the ferromagnetic phase transition temperature T-C in Ni nanowires. The electrical resistance measurements on well characterized Ni nanowires of diameters down to 20 nm were carried out over an extensive temperature range (4-675 K), which encompasses the region close to T-C (reduced temperature vertical bar t vertical bar <= 10(-2)). The wires were grown in porous alumina templates by electrodeposition and the experiments were carried out by retaining the wires in the templates. The strain that is generated by retaining the wires in the templates was estimated and its effect was considered in the analysis. The data analysis done in the framework of critical behavior of resistance near T-C reveals that the critical behavior persists even down to the lowest diameter wire of 20 nm. However, there is a suppression of the critical behavior of the resistivity as characterized by the critical exponent alpha and the amplitude of the derivative d rho(T)/dT at T-C. We observed a considerable suppression of T-C (as determined from resistance data). The shift in T-C as well as the suppression of d rho(T)/dT are explained as arising from finite size effects.