Thickness dependence of structure and magnetic properties of annealed [Fe/Pt]n multilayer films

Abstract

The L10 FePt phase material has potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. The heat treatment of [Fe/Pt]n multilayer films is one approach to form the L10 FePt phase at a lower processing temperature, which is highly desirable for its applications. This paper reports the influence of film total thickness (8–100 nm) on the structure and magnetic properties of annealed [Fe/Pt]n multilayer films. A novel technique based on hollow cone dark field transmission electron microscopy is used to determine the L10 phase fraction and grain size in the annealed films. It was found that the L10 phase fraction and grain size, ordering, and magnetic properties are strongly dependent on the total film thicknesses. An L10 FePt phase fraction close to 100% is achieved for a thick [Fe/Pt]n multilayer film (100 nm) annealed at 400 °C for 1 h, while a value of only 36% is achieved for a thin film (8 nm) annealed at the same condition. In this work the L10 FePt phase nucleation density is also presented. These results suggest that the L10 phase formation is nucleation limited, and that the subsequent growth of L10 phase grains also strongly influences the structure and magnetic properties of the annealed films.

Experimental measurements of the heats of formation of Fe3Pt, FePt, and FePt3 using differential scanning calorimetry

“…% for B and C, and > 10.5 at. % for B and E) The source of this difference in the transformation enthalpy for films C and D may be the diffusion of Fe into Pt to form the A1 FePt phase, [80][81][82][83][84][85] but occurring such that the calorimetry experiments are not able to directly measure the heat release associated with this diffusion, but can detect the "missing" heat. This diffusion occurs at all interfaces, but its impact on the measured enthalpy is magnified when more interfaces are present as has been seen in Ni/Al multilayer films where the diffusion region was estimated to be 4 nm thick.…”

“…The solid solution phase considered was (cFe,Pt), i.e., the face centered cubic, or A1 FePt, 60 which has been previously reported for annealed, sputter deposited Fe/Pt multilayers and for ball milled Fe-Pt samples. [80][81][82][83][84][85] The phases present at each stage of reaction are listed in Table II. To determine the volume percents of the phases present in the films annealed to the highest annealing temperature (725 C), the XRD intensities were corrected using the Lorentz, polarization, and Debye Waller factors in addition to a sample size correction factor, as detailed elsewhere. 86 The XRD patterns showed that the phases were 111 h i fiber-textured.…”

Nanomaterials by design: a review of nanoscale metallic multilayers

“…For instance, magnetic L1 1 CoPt and L1 0 FePt nanocrystalline and metastable alloys have been prepared from Co/Pt [406] and Fe/Pt [402,[407][408][409] systems, respectively, while TiNi alloys have been obtained from Ti/Ni multilayers [133,410]. The fast formation of ordered phases was made possible due to the existance of shorter diffusion paths between the coupled metals, which were made available by using individual layer thicknesses in the order of only a few nanometers (0.2-3 nm) [405,408,409,411].…”