Magnetism of Pt0.67Fe0.33Alloy

Abstract

PtFe alloys show a rich variety of magnetism with changing of Fe concentration and atomic configuration due to the competitive ferromagnetic and antiferromagnetic spin correlations. The PtFe alloys containing 18–40 at.% of Fe show the cubic Cu3Au type atomic order for which corners and face centers of fcc unit cell are occupied by Fe and Pt atoms, respectively and excess Fe atoms occupy the face center position. Vinokurova et al. studied the magnetism of Pt1 XFeX alloys with 0:3 < X < 0:35 and reported that the alloys show a ferromagnetic–antiferromagnetic (F–A) phase transition below TC. 3) The motivation of the present work is to investigate the magnetic phase transition of Pt1 XFeX alloys with these Fe concentration range. In this letter, we report the susceptibility and neutron diffraction data for a Pt0:67Fe0:33 alloy single crystal and propose a different model from the previous authors for the magnetism of Pt1 XFeX alloys with relevant Fe concentration range. A Pt0:67Fe0:33 alloy single crystal was grown by Bridgman method in a furnace with a carbon electrode under the Ar gas atmosphere. The SQUID system at Materials Characterization Central Laboratory in Waseda University was used for the magnetic susceptibility measurement. Both of zero field cooled (ZFC) and field cooled (FC) processes were measured at the temperature range between 5K and 250K in the magnetic field of 500Oe. Neutron scattering experiments were performed using T1-1 triple axis spectrometer installed in a thermal guide of JRR-3M, JAERI, Tokai. Incident neutrons with wavelength of 0.246 nm were used together with a thick pyrolitic graphite filter to eliminate the higher order contaminations. Magnetic susceptibility data are shown in Fig. 1. Ferromagnetic response appears at around 200K, but decreases below 100K. Since the FC data do not trace the same path with the ZFC data below 100K, the alloy shows a re-entrant spinglass like behavior. These data are consistent with those of the previous authors. Neutron scattering measurements were carried out for two different states of the specimen. At first, magnetic scattering measurements were performed for the as-grown sample. After the measurements, the specimen was annealed at 1000 C for 24 h to develop the atomic order. Then, the similar measurements were performed using the annealed specimen. Temperature variations of the ferromagnetic peak intensities studied at 1 0 0 and 1 1 0 and that of the antiferromagnetic peak at 1/2 0 0 for the as-grown sample are given in Fig. 2. The ferromagnetic peaks 1 0 0 and 1 1 0 appear at around 200K and the intensities increase with decreasing temperature down to 100K, then decrease below this temperature. The antiferromagnetic peak 1/2 0 0 appears at 120K. The antiferromagnetic peak intensity monotonously increases with decreasing temperature. The experimental data for the annealed specimen obtained by the similar measurements are given in Fig. 3. Temperature variations of the magnetic peaks are qualitatively the same, but the antiferromagnetic peak intensity for the annealed sample is almost twice of that for the as-grown sample, despite that the ferromagnetic peak intensities are almost the same. Since the line widths of these magnetic peaks were the same for the samples before and after annealing, these data 0 0.005 0.01 0.015 0.02