Session T17: Magnetic Alloys and Multilayers

8:00 AM–11:00 AM, Thursday, March 21, 2013
Room: 319

Sponsoring Unit: GMAG
Chair: Masatoshi Onoue, Northwestern University

Abstract ID: BAPS.2013.MAR.T17.4

Abstract: T17.00004 : Unusually sharp paramagnetic phase transition in thin film Fe$_{3}$Pt invar

8:36 AM–8:48 AM

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  Jasper Drisko
    (University of Maryland)

  John Cumings
    (University of Maryland)

Invar alloys, typically 3d transition metal rich systems, are most commonly known for their extremely low coefficients of thermal expansion (CTE) over a wide range of temperatures close to room temperature. This anomalous behavior in the CTE lends Invar to a variety of important applications in precision mechanical devices, scientific instruments, and sensors, among others. Many theoretical models of Invar have been proposed over the years, the most promising of which is a system described by two coexisting phases, one high-spin high-volume and the other low-spin low-volume, that compete to stabilize the volume of the material as the temperature is changed. However, no theory has yet been able to explain all experimental observations across the range of Invar alloys, especially at finite temperature [1]. We have fabricated thin films of a Fe$_{3}$Pt Invar alloy and investigate them using Lorentz Transmission Electron Microscopy (TEM). 23nm films are deposited onto SiN membrane substrates via radio-frequency magnetron sputtering from a pure Fe target decorated with Pt pieces. We observe novel magnetic domain structures and an unusually sharp phase transition between ferromagnetic (FM) and paramagnetic (PM) regions of the film under a temperature gradient. This sharp transition suggests that the FM-to-PM transition may be first order, perhaps containing a structural-elastic component to the order parameter. However, electron diffraction reveals that both the FM and PM regions have the same FCC crystal structure. \\[4pt] [1] Kakehashi, Y., \textit{Phys. Rev. B.} \textbf{38}, 474 (1988).

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