Influence of substrate temperature and post annealing on morphology and magnetic properties of pulsed laser deposited Fe
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Influence of substrate temperature and post annealing on morphology and magnetic properties of pulsed laser deposited Fe50-Ni50 films. Sally A. Ibrahim1, Svitlana Fialkova1, Kwadwo Mensah-Darkwa1, Sergey Yarmolenko1, and Dhananjay Kumar1 1 North Carolina A&T State University, 1601 E. Market St. Greensboro, North Carolina, 27411, U.S.A. ABSTRACT As the need for smaller data storage devices in the market continues to grow, the study of new combinations of self-assembled magnetic nanoparticles/films is greatly needed. In this research, Fe50-Ni50 films were synthesized using a Pulsed Laser Deposition technique. The films were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and physical properties measurement system (PPMS). Films were deposited from Fe-Ni alloy target (50%-50% composition), deposition was conducted in vacuum, at substrate temperatures varying from liquid nitrogen temperature -196°C to 600°C. The films were annealed in a vacuum chamber at 600°C for 1 hour. The study reveals that the substrate temperature has significant effect on the structure of the films and their magnetic properties. It was shown that additional thermal treatment improved the quality of films in terms of narrow grain size distribution. Magnetic properties were also found to improve significantly after post annealing process. INTRODUCTION Magnetic thin films have been utilized in many applications such as sensors, actuators and magnetic recording media (such as hard drives, CDs, DVDs and USB flash drives) [1, 2]. Researchers have been concentrating in increasing the storage capacity of these devices to compete with the miniaturization demands of the market. The FeNi alloys are considered good candidates for magnetic recording media because of its economic competence compared to FePt and FeCo which are noble and need complex processing. Previous studies on ZnO/Co multilayers deposited by pulsed laser deposition and annealed at elevated temperatures caused the thin films to transform from the amorphous phase to crystalline ZnO/Co phase. Formation of CoO and ZnCo2O4 which are antiferromagnetic along with the ferromagnetic metallic crystalline Co allowed FM-AFM coupling and therefore widening of the hysteresis loop [3]. The coercivity calculated from the hysteresis loop is an important parameter that indicates the resistance to demagnetization which is preferred in data storage devices. Soft magnetic alloys such as FeNi need manipulation to increase their coercivity[4]. In this study Fe50Ni50 thin films are fabricated by pulsed laser deposition at different substrate temperatures. The samples were then annealed in a vacuum chamber at 600°C for 1 hour. The as deposited and annealed thin films were characterized using SEM, AFM and PPMS to study the effect of post annealing on their magnetic properties.
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EXPERIMENT Fe50Ni50 alloy was prepared at University of Nebraska. Fe and Ni metal powders with 50% weight were mixed for 30 minutes in a sealed ball milling container. The powders were then melted using a
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