Magnetic Order of Co 0.1 Pt 0.9 in Proximity of CoPt 3
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H Fig. I Schematic diagram of a scattering experiment using a beam of (X-rays) neutrons with spins aligned anti-parallel (spin-up) or parallel (spin-down) to the field, H, applied to the sample. Inset: diagram of the Coo IPto09-CoPt3 bilayer sample. Sample Characterization The susceptibility of a similarly prepared sample was measured with a vibrating sample magnetometer equipped with an liquid-N 2 flow cryostat. Kinks in the susceptibility curve measured as a function of temperature were observed at 540K and 240K. The kink at the higher of the two temperatures corresponded to the onset of ferromagnetic order in the CoPt 3 underlayer, i.e. its Curie temperature, Tc. The low temperature kink corresponded to the Curie temperature of the Coo IPt09 overlayer. The thickness of the Coo .Pto 9 and CoPt3 films, and the roughness of the air-film, CoO 1Pt0 .9-CoPt and film-substrate interfaces were measured with X-ray reflectometry. Reflectometry involves measuring the intensity of the radiation specularly reflected by a smooth sample through an angle, 2(x (see Fig. 1), and comparing this intensity to the intensity of the radiation illuminating the sample. The ratio, called the reflectivity- R, is measured as a function of momentum transfer, Q--4tsin((x)/X, where ;, is the wavelength of the radiation. The X-ray reflectivity of the sample was measured using X-rays with a wavelength k=1.54178A, selected from a spectrum with a graphite monochromator. X-rays were produced by an 18kW rotating anode X-ray generator at the Los Alamos Neutron Science Center (LANSCE). The X-ray beam was collimated with a pair of slits located between the monochromator and sample. The intensity of the incident X-ray beam was monitored using a scintillation detector and a Mylar sheet, which scattered a small portion of the X-ray beam into the detector. The intensity of the incident X-ray beam was needed in order to measure the exposure of the sample to the beam. The position and intensity of the reflected X-ray beam were measured with a Xe-filled position sensitive detector (PSD). The intensity profile measured as a function of angle off the sample surface by the PSD was a Gaussian-shaped peak on a smooth background. The integrated intensity of the peak after removal of the background was the reflectivity of the sample at Q, which was determined by selecting the angle of incidence- the angle, ot, between the incident X-ray beam and its projection on the sample surface. The profile was assembled by incrementing a, and repeating the measurement and integration procedure. The reflectivity profile taken for the sample at 296K is shown in Fig. 2. X-ray reflectivity measurements were also taken at 81 and 248K with the aide of a Displex closed-cycle He cryostat equipped with Be-domes. The three X-ray reflectivity profiles were not statistically different.
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X-ray reflectivity of bilayer sample taken at 296K
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