Evolution of structural and magnetic properties of FePtCu alloy films on annealing of FePt/Cu multilayers

Thin films of ternary (FePt)100-xCux alloys were obtained by annealing of FePt (100 Å)/Cu (d Å) multilayers with d = 50 and 100 Å deposited by sputtering at room temperature on Si substrates. The evolution of structural and magnetic properties of these multilayers induced by isochronal and isothermal annealing in a vacuum has been studied using depth dependent characterization techniques. Isochronal annealing for 0.5 h at different temperatures (300 to 600 °C) showed very low interdiffusion at the interfaces with no signature of alloy phase formation. However, isothermal annealing of multilayers at 600 °C for longer times (1.5-6.5 h) showed significantly large interdiffusion accompanied by the formation of polycrystalline ternary alloy and iron silicide phases. The iron silicide formed at the substrate-film interface assists the growth of the L10 ordered ternary alloy phase, which showed different stoichiometry for different multilayers. The L10 phase formed with higher Cu content showed drastically different magnetic properties with a reduction in saturation magnetization and an increase in coercivity (∼6 kOe) at room temperature. The iron silicide formed on high temperature annealing showed ferromagnetic nature with a magnetization of ∼140 emu cm-3 at room temperature.

Interface induced magnetic properties of Gd/Co heterostructures

Antiferromagnetic coupling between rare-earth and transition metal ferromagnetic layers gives rise to various magnetic ground states in heterostructures of these materials. Interface structure and morphology tend to play important roles in magnetic properties of such systems. Interface induced magnetization in Gd/Co heterostructures has been studied using a combination of structural and magnetic characterization techniques. The interface morphology of the Gd/Co system was varied by growing Gd/Co multilayers using magnetron sputtering under different argon partial pressures. Interfacial properties were further modified by annealing the multilayers under high vacuum. The macroscopic magnetization measurements have been correlated with depth dependent structure and magnetic properties of multilayers studied using X-ray and polarized neutron reflectometry techniques. Secondary ion mass spectrometry measurements from both as-deposited and annealed samples also confirmed modification at the interfaces. It has been shown that the interface structure, together with roughness, leads to a unique low-temperature magnetic phase characterized by twisting of Gd and Co moments.