Annealing induced compositional changes in SmCo5/Fe/SmCo5 exchange spring trilayers and its impact on magnetic properties

• SmCo5 (25 nm)/Fe (8 nm)/SmCo5 (25 nm) trilayers were grown by sputtering.
• Effect of annealing on the interphase chemistry was investigated using RBS.
• Optimal interphase coupling with good phase chemistry was observed at 773 K.
• Enhanced Hc (814 kA/m) and (BH)max (243 kJ/m3) values were achieved at 773 K.

SmCo5/Fe/SmCo5 sandwich configurations have gained renewed interest when compared to the conventional SmCo5/Fe bilayers, as they exhibit enormous scope to impart high energy product values with strong magnetization reversal behavior. The compositional changes that occur in the intermediate soft layer upon annealing play a critical role in determining the phase chemistry, as well as magnetic performance of the trilayers and herein we address such a study. SmCo5/Fe/SmCo5 sandwich films with fixed layer thicknesses of SmCo5 (25 nm) and Fe (8 nm) were grown by sputtering on Cr buffered Si (1 0 0) substrates and subsequently, annealed at different temperatures: 673, 773 and 873 K. The effect of post-deposition annealing on the structure, composition and magnetic properties of the trilayer architecture was investigated by X-ray diffraction (XRD), Rutherford back-scattering (RBS) and super-conducting quantum interference device (SQUID), respectively. The XRD studies showed significant decrease in the lattice parameter values with increasing annealing temperature, which suggests an increase in the diffused Co-content in the Fe-intermediate layer. The XRD results were further validated by RBS measurements, which confirmed that both composition and thickness of the Fe-intermediate layer were strongly affected by the annealing temperature. The SQUID measurements demonstrated the existence of in-plane anisotropy and strong exchange coupling between the hard and soft layers for all the annealed sandwich films. The trilayer stack annealed at 773 K showed the best magnetic performance such as high coercivity (814 kA/m), remanence (944 kA/m) and energy product (243 kJ/m3).