Effect of substrate temperature on the crystallographic structure and first-order magnetic phase transition of FeRh thin
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this article, the effects of substrate temperature on the crystallographic structure and first-order magnetic phase transition in iron-rhodium (FeRh) thin films are investigated. It was found that for the as-deposited FeRh thin films, 350–400 °C is the optimal range of substrate temperature for obtaining B2 ordered FeRh thin films. After postannealing, it was shown that 400 °C is the optimized substrate deposition temperature for obtaining the best chemical/atomic ordering in postannealed FeRh thin films. Magnetization studies indicate that the as-deposited FeRh thin film with substrate temperature of 350 °C does not show a first-order antiferromagnetic (AFM)- to-ferromagnetic (FM) phase transition behavior during heating process and it gives a typical FM behavior whereas the as-deposited FeRh thin film deposited at 400 °C shows a broad first-order AFM-to-FM phase transition during heating and cooling processes. Both the postannealed FeRh thin films deposited at 350 and 400 °C give a clear first-order AFM-to-FM phase transition with a residual magnetization of about 50–100 emu/cc. The residual magnetization may possibly be caused by the disordered bcc (a) FM phase, B2 ordered (a9) FM phase or a near-surface/interfacial ferromagnetism in the ordered FeRh thin films. I. INTRODUCTION
Ordered B2-type (CsCl structure) iron-rhodium (FeRh) alloys have been subject of theoretical and experimental studies due to their interesting properties such as magnetocaloric effect,1 elastocaloric effect,2 giant magnetostriction3 and giant magnetoresistance4 occurring close to room temperature. These interesting characteristics in this alloy system are thought to arise due to a first-order magnetostructural phase transition from an antiferromagnetic (AFM) to ferromagnetic (FM) state when heating beyond a critical transition temperature (Ttr). This property has created great interest in thin films of this material to be used for temperature-dependent exchange coupling layers in heat-assisted magnetic recording5 and magnetic random access memory (MRAM) applications.6 The first-order magnetostructural phase transition is sensitive to FeRh composition and fabricating conditions, therefore there is a large variation in AFM-to-FM transition behavior reported in the literature.7–9 Early study on FeRh thin films was done by electron beam melting on amorphous substrates but the low amount of ordering and the compositional fluctuations of these films resulted in broad magnetic transitions.10 Recently, sharp magnetic transitions were demonstrated in evaporated films on MgO (001) single crystal substrates and sputtered films on glass substrates in a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.61 1042
J. Mater. Res., Vol. 28, No. 8, Apr 28, 2013
our studies.11,12 In addition, the first-order magnetostructural phase transition behavior of ordered FeRh alloy depends on the microstructure, temperature, external magnetic field and pressure greatly. During the process of deposition, diffusion is the main moving mode of sur
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