Effect of substrate temperature on the magnetic properties of epitaxial sputter-grown Co/Pt

Abstract

Epitaxial Co/Pt films have been deposited by dc-magnetron sputtering onto heated C-plane sapphire substrates. X-ray diffraction, the residual resistivity and transmission electron microscopy indicate that the Co/Pt films are highly ordered on the atomic scale. The coercive field and the perpendicular magnetic anisotropy increase as the substrate temperature is increased from 100-250C during deposition of the Co/Pt. Measurement of the domain wall creep velocity as a function of applied magnetic field yields the domain wall pinning energy, which scales with the coercive field. Evidence for an enhanced creep velocity in highly ordered epitaxial Co/Pt is found. 2Co/Pt multilayers have been studied for a number of years 1,2 , initially because of their potential as magneto-optical recording media 3 . Their attractive properties include perpendicular magnetic anisotropy (PMA) and a large polar magneto-optic Kerr effect (MOKE) at short wavelengths 4 . More recently Co/Pt has become an interesting system for the study of the physics of domain walls (DWs) [5][6][7][8] , and spin torque [9][10][11][12][13] . The PMA leads to the formation of narrow, nanometre-scale DWs, and the large polar Kerr effect is convenient for measuring the DW motion. However, DWs tend to pin at grain boundaries in the polycrystalline Co/Pt that is typically used in these studies 9 , and this is an issue not only for investigations of the fundamental physics of DWs but also for future devices which may depend upon reliable DW motion, such as racetrack memory 14 . Epitaxial Co/Pt, in which the density of grain boundaries is minimised, could provide a solution to this problem. Ideally, however, the method of multilayer deposition should be compliant with industrial processes.Sputtering is a convenient, cost-effective technique for thin film deposition and may be used to grow films epitaxially if a single crystal substrate is heated to an appropriate temperature.In order to obtain PMA in epitaxial Co/Pt, the films are required to grow in the (111)-orientation 15 , and (111) texture was first seen in sputtered Co/Pt in 1993 16 . While there have been studies of Co/Pt superlattices 17 and Pt/Co/Pt sandwiches 18 grown by sputtering, there has been no optimisation of sputtered epitaxial Co/Pt (111) for DW devices. Here we show how the substrate temperature may be used to tune the magnetic properties of epitaxial Co/Pt grown on sapphire.First, the growth of Pt on C-plane (0001) sapphire was optimised. A 60 nm Pt film was deposited at various substrate temperatures in the range 400-700C. High angle X-ray scans all had a clear peak between 39.5 and 40, indicating (111) structure (see Figure 1). The 3 peak was largest and the satellite peaks were best defined for a deposition temperature of 500C indicating that at this temperature the crystal quality of the film was highest. It was also found that overnight annealing of the sapphire substrate at 700 C improved film quality. X-ray reflectivity curves were measured from Pt films deposited both after a s...

Tuning spin–orbit torques at magnetic domain walls in epitaxial Pt/Co/Pt1−x Au x trilayers

“…We studied Pt(3 nm)/Co(0.8 nm)/Pt 1−x Au x (3 nm) trilayers with x = 0, 0.5, and 1 that were prepared by sputtering at high temperatures, as described previously [38,39]. The main points of the growth method are that a seed Pt layer was sputtered onto a C-plane sapphire substrate at 500 • C, followed by Co at a substrate temperature of 100 • C. The Pt 1−x Au x layer was grown by co-sputtering from Pt and Au targets at 100 • C, with the sputtering powers adjusted to keep the rate ∼ 1Å/s.…”

Magnetic properties and field-driven dynamics of chiral domain walls in epitaxialPt/Co/AuxPt1−xtrilayers

“…To avoid such ambiguities and in order to explore this systematically one has to grow such materials in a controlled way. Here we experimentally investigate epitaxial layers of Pt/Co/Au x Pt 1−x prepared by sputtering onto single crystal sapphire substrates 18 . Pt is a common pairing with Co that has strong PMA and DMI 16 , and is close to satisfying the Stoner criterion 19 , giving strong proximity magnetism.…”

Effect of interfacial intermixing on the Dzyaloshinskii-Moriya interaction in Pt/Co/Pt

“…• C, where a high degree of crystallographic ordering was found previously [28]. Films were grown with the base pressure in the range 1.1 × 10 −7 to 3.3 × 10 −7 Torr, measured immediately prior to deposition of the seed layer.…”

“…• C for optimum smoothness [28]. Measurements of the residual resistivity ratio (RRR) and the full width at half maximum (FWHM) of the x-ray diffraction rocking curves in previous work [28] showed that sputtering onto a C-plane sapphire substrate held at a temperature between 450…”