S.H. Liu

Effect of Annealing Process on Residual Strain/Stress Behaviors in FePt Thin Films

We have characterized the dependence of residual strain/stress on annealing process (post- and in-situ annealing) in single-layer FePt films prepared by sputtering onto amorphous glass substrates. A remarkable difference of evolutions in residual strains between post-andin-situ annealed samples was observed by Sin2 ψ method using synchrotron radiation. The onset of ordering temperature for both series samples is almost identical (~ 350 °C), verified by x-ray diffraction. Crystalline domain size, measured by x-ray peak breadths, of FePt films indicates a difference between these two series samples, which is associated with evolution of residual strain. We believe that the dynamic stress relaxation is the major factor in discrepancy of the residual stress behavior, since the atomic mobility of adatoms during film deposition for in-situ annealing samples are much higher than that for post-annealed films. It is further deduced that residual strain mechanisms may influence the ordering behaviors and related microstructure of FePt films.

Ordering Transformation of FePt Thin Films by Initial Stress/Strain Control

The influence of initial stress/strain state on ordering of FePt is studied. The internal stress of FePt thin films deposited at room temperature can be successfully controlled in a wide range from compressive 0.95 GPa to 1.1 GPa tensile by adjusting sputter distance and inserting underlayer with different thickness. Ordering process is triggered by rapid thermal annealing at 350 for 15 min. Structural and magnetic results confirm that order transformation occurs within the stress range of . Highly stressed initial states (either compressive or tensile) suppress ordering in different ways. Large compressive stress increases the energy barrier of order reaction which results in volume expansion; strong tensile stress block the formation of phase by preventing the densification, a vital process prior to ordering, which creates intensive tensile stress. The results provide an insight into the ordering process in the aspect of evolution of internal stress/strain.

Effect of Annealing Process on Strain-Induced Crystallographic Orientation of FePt Thin Films

Dependence of the crystallographic orientation on annealing process (post- and in-situ annealing) of in the 40-nm-thick single-layered FePt films fabricated by magnetron sputtering onto glass substrates have been investigated. The progress of L10 ordering for both series of samples is nearly the same, verified by X-ray diffraction. For the post-annealing films, there is a dramatic change of crystallographic orientation from (111) to (001) planes with an increase of temperature from 350 °C to 700 °C. On the contrary, the orientation evolves from a (111) texture to isotropic state for the in-situ annealing samples in the same temperature range. The different atomic mobility during annealing leads to a discrepancy in the residual stress behavior and microstructure, which further causes the disparity of crystallographic orientation.

A comparison of the rapid-annealed FePt and FePd thin films: Internal stress, L1 0 ordering, and texture

Rapid thermal annealing (RTA) techniques have been widely used in materials engineering. Recently, use of RTA has also considered as an efficient way to control the crystal structure and microstructure of the magnetic materials. L1 0 FePt and FePd have been drawn much attention due their remarkable magnetocrystalline anisotropy (> 107 erg/cm3) [1]. Generally, as-prepared FePt and FePd thin films at ambient temperature are chemically disordered and soft magnetic properties. RTA has been used to improve ordering transformation and control crystal orientation as well as surface morphology of the L1 0 FePt films. However, there are few reports focusing on the L1 0 -FePd films annealed by RTA. In this work, we aim to investigate the difference in crystal structure and magnetic properties between FePt and FePd thin films using RTA. The preferred orientation, L1 0 ordering and initial stress of the FePd and FePt films were compared and discussed.