Exchange Spring Type Magnet Realized in FePt/Fe Multilayers Deposited by Magnetron Sputtering
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J4.3.1
Exchange Spring Type Magnet Realized in FePt/Fe Multilayers Deposited by Magnetron Sputtering Yousong Gu, Dayong Zhang, Xiaoyuan Zhan, Zhen Ji, Xiaolan Zhen, Yue Zhang* Department of Material Physics, University of Science and Technology in Beijing Beijing 100083, People’s Republic of China ABSTRACT Series of FePt/Fe multilayers with different layer thicknesses have been deposited on Si substrates by magnetron sputtering and post annealing at different temperatures and durations. The structure, surface morphology, composition, and magnetic properties of the deposited films have been characterized by XRD, SEM, EDX and VSM. It is found that after annealing at temperatures above 500˚C, FePt phase undergoes a phase transition from disorder fcc into ordered fct structure, and become a hard magnetic phase. For [FePt/Fe]n multilayer with varying Fe layer thickness, lattice constants and grain sizes change with Fe layer thickness and annealing temperature. The coercivities of [FePt/Fe]n multilayers decrease with Fe layer deposition time, and the energy product (BH)max shows a maximum with Fe layer thickness. Optimization on layer thickness leads a high (BxH)max value of 15.2MGOe for [FePt(8min)/Fe(4min)]8. The effects of quick annealing and Ag underlayer on the structure and magnetic properties were also studied. INTRODUCTION Exchange spring magnet is often found in exchange coupled nano-composites with hard/soft magnetic phases. It is an interesting subject of study in obtaining improved permanent magnets by employing nanotechnology and the concept of material design[1,2]. Energy product (BxH)max is an obvious benchmarks of this kind of structures and it is predicted by theoretically calculation that the energy product can be as high as 1 MJ/m3[3]. Recently, considerable attentions have been focused on the magnetic properties of Fe-Pt alloys for its very high magnetocrytalline anisotropy energy (Ku≈7×106J/m3), high coercivity, good corrosion resistance and large energy product (BH)max [4]. It is widely studied for application as high density recording media [5]. The magnetic properties of FePt phase is strongly effected by ordering and structure[6]. The growth method, post annealing parameters, doping and under or capping layer can also effect the structure and magnetic properties [7-8]. Exchange spring type materials with FePt are also very good candidates for permanent magnet with theoretically predicted energy product of 90MGOe in FePt/Fe [9]. However, its magnetic properties strong depend on the composition and microstructure [10]. Hence, structural modification is very important for this kind of materials. A energy product as high as 50MGOe has been obtained in rapidly annealed nanoscale Fe/Pt multilayers[11]. By self-assembly of nano *
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J4.3.2
particles and subsequent annealing, exchange coupled FePt/Fe3Pt nanoparticles showed a high energy product of 20.1MGOe [12]. In this work, [FePt/Fe]n multilayers were deposited by magnetro
