Formation of L1₀-ordered CoPt during interdiffusion of electron-beam-deposited Pt/Co bilayer thin films on Si/SiO₂ substrates by rapid thermal annealing

Abstract

Preparation of ordered CoPt on Si substrates is significant for expanding future applications of spintronic devices. In this study, ordered CoPt alloys including the L1 0 phase with a maximum coercivity of 2.1 kOe are formed in electron-beam-deposited 11.4 nm thick Pt/Co bilayer thin films on Si/SiO 2 substrates via interdiffusion during rapid thermal annealing (RTA). The effects of RTA temperature on the magnetic properties, crystal structures, cross-sectional elemental profiles, and surface morphologies of the films are analyzed by vibrating sample magnetometer (VSM), grazing incidence x-ray diffraction (GI-XRD), energydispersive x-ray spectroscopy (EDX), and scanning electron microscope (SEM), respectively. For the asdeposited film, polycrystalline Pt was confirmed by uniform Debye-Scherrer rings of Pt. At 200°C, interdiffusion between Co and Pt atoms in the film started to be observed by EDX elemental maps, and at 300°C, alloying of Co and Pt atoms was confirmed by diffraction peaks corresponding to A1-disordered CoPt. At 400°C, the in-plane coercivity of the film began to increase. At 700°C, ordered CoPt alloys were confirmed by superlattice diffraction peaks. At 800°C, a graded film containing L1 0 -ordered CoPt was found to be formed and a maximum coercivity of 2.1 kOe was observed by VSM, where the easy axis of magnetization was oriented along the in-plane direction. At 900°C, deformation of the ordered CoPt alloys was observed by GI-XRD, and the grain size of the film reached a maximum.

Nanostructure-induced L10-ordering of twinned single-crystals in CoPt ferromagnetic nanowires

“…Therefore, the c and a values for the L1 0 -CoPt nanowires were determined to be c ¼ 3.6804 A and a ¼ 3.7799 A, respectively, which agrees with values in the literature. 32,[50][51][52]68,70,91 The magnetic hysteresis loops (M-H curves) of the nanowires aer annealing at 650 C for 90 min are shown in Fig. 4.…”

“…Therefore, the c and a values for the L 1 0 -CoPt nanowires were determined to be c = 3.6804 Å and a = 3.7799 Å, respectively, which agrees with values in the literature. 32,50–52,68,70,91…”

“…The crystal structures of the nanowires were characterized by GI-XRD method using the synchrotron radiation at the BL-8B line of the Photon Factory, High Energy Accelerator Research Organization (KEK), Japan. [50][51][52] The measurements were performed using an X-ray diffractometer (R-Axis, Rigaku). A monochromic synchrotron X-ray beam at a wavelength of 1.05303 Å was irradiated onto the sample with grazing incidence angles.…”

“…44 We also reported the L1 0 -ordering of Co/Pt multilayer thin lms on thermally oxidized Si (Si/SiO 2 ) substrates by EB evaporation and annealing processes, which was characterized by scanning electron microscope (SEM), grazing incidence X-ray diffraction (GI-XRD), and vibrating sample magnetometer (VSM). [50][51][52] In Pt (6.6 nm)/Co (4.8 nm) bilayer thin lms, graded lms consisting of L1 2 -ordered CoPt 3 , L1 0 -CoPt, and L1 2ordered Co 3 Pt were formed during interdiffusion of the bilayer annealed at 800 C for 30 s by RTA in a vacuum. 50 Because the interdiffusion and L1 0 -ordering of CoPt were in progress owing to the short annealing time of 30 s RTA process and both L1 2 -CoPt 3 and L1 2 -Co 3 Pt do not usually show large H c , an H c in the graded lms was as small as 2.1 kOe.…”

“…[50][51][52] In Pt (6.6 nm)/Co (4.8 nm) bilayer thin lms, graded lms consisting of L1 2 -ordered CoPt 3 , L1 0 -CoPt, and L1 2ordered Co 3 Pt were formed during interdiffusion of the bilayer annealed at 800 C for 30 s by RTA in a vacuum. 50 Because the interdiffusion and L1 0 -ordering of CoPt were in progress owing to the short annealing time of 30 s RTA process and both L1 2 -CoPt 3 and L1 2 -Co 3 Pt do not usually show large H c , an H c in the graded lms was as small as 2.1 kOe. 50 In [Co (1.2 nm)/Pt (1.6 nm)] 4 multilayer thin lms, isolated round grains of singlephase L1 0 -CoPt were formed aer annealing in a vacuum at 900 C for approximately 60 min, which exhibited an improved H c of 2.7 kOe due to the sufficient interdiffusion by multilayered structure and extended annealing time.…”