Microstructural Evolution during Post Deposition Annealing of Pulsed Laser Deposited Fe(100-x) Pdx Thin Films
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0980-II03-08
Microstructural Evolution During Post Deposition Annealing of Pulsed Laser Deposited Fe(100-x) Pdx Thin Films Andreas Kulovits, John Leonard, and Jorg Wiezorek Mech. Eng. & Mat. Sci., University of Pittsburgh, 848 Benedum Hall, Pittsburgh, PA, 15261 ABSTRACT Thin films of different composition FeXPd1-X, X= 50, 60, were deposited by pulsed laser deposition (PLD) on amorphous SiO2 and Si3N4. We characterized the microstructural evolution of different order/disorder phase-transformations during post-deposition annealing relative to the as-deposited state in terms of morphology, grain size, texture and presence of chemical order using SEM, XRD and TEM. VSM measurements were used to monitor magnetic properties. Differences in the microstructural parameters are attributed to different solid state transformations of FCC to L10 ordering and concomitant phase separation of α–Fe vs. FCC to L10 ordering upon heat treatment. Relationships of the different phase transformation products to properties are discussed. INTRODUCTION FePd belongs to the family of intermetallics with interesting magnetic properties that undergoes a FCC to L10 ordering transformation [1]. In contrast to FePt the Fe rich compositions, for Fe-Pd an L12 ordered Fe3Pd phase does not exist, but rather phase separation into α–Fe and L10 ordered FePd occurs (Fig. 1). A careful study of the Fe rich
Figure 1: Binary FePd phase diagram including schematic extensions of metastable phase fields, marked in dotted lines
part of the FePd phase diagram shows that many different stable and metastable phase transformation modes are possible. For example, thermo-elastic martensite forms upon quenching a Fe34Pd66 alloy from the FCC phase field to room temperature [2]. To optimize magnetic or other properties of these alloys the phase transformation behavior during processing has to be understood. For this reason numerous investigators have been studying these alloys in bulk as well as thin film form [3-5]. For polycrystalline thin film preparation usually magnetron sputtering, is used [6]. Here pulsed laser deposition (PLD) has been used to obtain thin films of the compositions Fe50Pd50 and Fe60Pd40. PLD uses a high-energy laser to irradiate a target, producing a plasma that subsequently impacts the film substrate. Ablation rates for different materials are typically very similar, resulting in reproduction of target compositions in PLD films. Thus, possible high deposition rates and the excellent compositional control for alloy and complex multi-element compound thin films are considered the main advantages of PLD. Here the microstructure evolution of PLD thin films FeXPd1-X, X= 50, 60, deposited at room temperature and elevated substrate temperature have been compared and rationalized. Furthermore, the effects of subsequent annealing on microstructure and properties have been investigated. EXPERIMENTAL Fe50Pd50 and Fe60Pd40 targets have been produced form high-purity elemental starting materials using vacuum arc melting in a purified Argon gas atmosphere.
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