Magnetic force microscopy of combined reaction-processed polycrystalline equiatomic bulk L1 0 FePd
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Timothy J. Klemmer Seagate Research, Pittsburgh, Pennsylvania 15222-4215 (Received 8 March 2008; accepted 20 October 2008)
In this work, the correlation between magnetic-domain structure and microstructure in combined reaction-processed equiatomic L10 FePd has been investigated using magnetic force microscopy. The microstructure consisted of approximately equiaxed grains with an average grain size of 1 mm and a grain size distribution ranging from below the theoretical critical domain size (Dcrit0.2–0.3 mm) up to approximately 5 mm in diameter. The domain structure was characterized as “mixed” in nature, consisting of smaller single-domain grains, larger multidomain grains, and a larger scale interaction domain structure encompassing many grains. The domain boundaries separating interaction domains tended to lie along grain boundaries, and it is proposed that the observed interaction domains should be considered in descriptions of the magnetization and magnetization reversal behavior of this material. In particular, pinning of interaction domain walls by intragranular features of the microstructure such as grain boundaries and single-domain grains could play a role in the measured coercivities.
I. INTRODUCTION
L10-ordered ferromagnetic intermetallics, such as FePd, FePt, and CoPt, are of technological interest due to large uniaxial magnetocrystalline anisotropies (K1 FePd 2 107 erg/cm3) and good mechanical properties.1 However, the intrinsic coercivity (Hci) and the remanent magnetization (Mr) depend strongly on the microstructure established during processing.2 By using thermomechanical processing, various morphologically different microstructures exhibiting planar crystal defects, including grain boundaries (GBs), antiphase boundaries (APBs), stacking faults (SFs), and microtwins (mTs), have been obtained in L10 FePd.1–6 Hence, L10 FePd provides a model system for fundamental studies of the interaction between magnetic-domain structure and microstructural features in narrow domain wall (d11.5 nm) bulk permanent magnet materials exhibiting large uniaxial magnetocrystalline anisotropy. The different microstructural morphologies result in intrinsic coercivities ranging from approximately 10 to 20 Oe for magnetically “soft” single-domain crystal a)
Address all correspondence to this author. Present address: Materials Science and Engineering Department, Carnegie Mellon University, PA 15213. e-mail: [email protected] b) Present address: GE (Lighting Technology), Willoughby, OH 44094. DOI: 10.1557/JMR.2009.0324 J. Mater. Res., Vol. 24, No. 8, Aug 2009
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samples, 200 to 500 Oe for conventionally processed polytwinned polycrystalline samples,1 500 to 1850 Oe for combined reaction processed (CRP) polycrystalline samples,2,3,5,7,8 and 2000 to 5000 Oe in nanostructured thin films and mechanically alloyed powder samples.4,6 The L10-type FePd alloys have served as a suitable material system for the study of domain-wall pinning by planar defects and microstr
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