In an earlier paper we have reported about prelimary results of evaporated CoNi/Pt multilayers [I] The main result at that time was a substantially lower Curie temperature for a C0 6o Ni4oIPt multilayer in comparison with the known Co/Pt having the same magnetic parameters. A study of the bulk magnetic phase diagrams shows a lowered Tc for adding Ni into Co. The problem by tailoring the composition for the Te is that one also have to consider the Kerr rotation because this value scales with the magnetic moment of the multilayer. Experimental CosoNiso/Pt ll1ultilayers have been sputtered at Par = 1.6•' 0-2 mbar after obtaining an Phack :::; 10-8 mbar. The target-substrate distance was 100 mm and the substrate temperature was ambient. Deposition rate used were 0.13 nmJs for the CoNi and 0.3 nmls for the Pt layer. A Pt seedlayer was used on a substratc of glass or Si(100). The MO characterization (polar Kerr rotation and ellipticity) was carried out at wave1enghts of 1.3-4.0 eV at a max field of 0.6 T. With a special stage temperature dependent KCl.,. Il1cnsurClUents from RT to 40QoC have been performed. Cross~section and plane view TEM samples have been prepared and studied with a Philips CM30-STEM microscope (see fig la). Domain observations were done with this microscope and MFM.
Two-dimensional (2D) ferromagnets with high Curie temperature (TC) are highly desirable due to their potential applications in spintronic devices. However, they are rarely obtained in experiments mainly due to the challenge of synthesizing high-quality 2D crystals, and their TC values are below the room temperature. By first-principles calculations, herein we design a family of stable 2D FenGeTe2 (4≤n≤7) ultrathin films that are similar to the reported Fe3GeTe2, which exhibit coexistence of itinerant and localized magnetism. Among them, 2D Fe3GeTe2 and Fe4GeTe2 are ferromagnetic metals with TC of 138 K and 68 K, respectively; 2D Fe5GeTe2, Fe6GeTe2 and Fe7GeTe2 ultrathin films are Néel’s P-types, R-type, R-type ferrimagnetic metals with TC of 320 K, 450 K and 570 K, respectively. The thickness induced magnetic phase transition is mainly originated from the competition between itinerant and localized states, which is also correlate well with the content of Fe3+ and Fe2+ ions. A valence/orbital dependent magnetic exchange model is proposed to clarify such interesting thickness and composition effect. Our results not only endow 2D Fe-Ge-Te ultrathin films as promising candidates for spintronics at room temperature, but also propose a universal mechanism to understand the magnetic coupling in complex magnetic systems.
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