Effect of Mn addition on the thermal stability and magnetic properties of rapidly-quenched L10 FePt alloys. (October 2015)

• Record Type: Journal Article
• Authors: Crisan, O.; Crisan, A.D.; Mercioniu, I.; Pantelica, D.; Pantelica, A.; Vaucher, S.; Nicula, R.; Stir, M.; Vasiliu, F.
• Is Part Of: Intermetallics. Volume 65(2015:Oct.)
• Page Start: 81
• Page End: 87
• Publication Date: 2015-10
• Subjects: Magnetic alloys -- Magnetic properties -- Nanocrystalline structure -- Thermal stability -- Electron microscopy -- X-ray diffraction; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2015.06.008
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: Nano-composite magnets with L 10 structure derived from binary FePt alloys and prepared as melt-spun ribbons are of current interest due to their higher operating temperature and the ability to be cast as a two-phase magnet with exchange spring magnetic properties, as both soft and hard magnetic phase may emerge from the same metastable precursor, i.e. the disordered cubic A1 phase. The present paper studies the effect of Mn addition on the thermal stability and phase structure, on the abundance of the hard magnetic phase and relative proportion of the soft ones, on the microstructure of the alloy as a function of temperature and on the overall magnetic properties. The interplay of the various magnetic sublattices in the ordering of the L 10 phases as a consequence of introducing antiferromagnetically coupled Mn atoms in the alloy composition is discussed and interpreted in terms of microstructural changes induced by this addition as revealed by high resolution transmission electron microscopy and X-ray diffraction. The temperature evolution of the phase composition and structural parameters is monitored using synchrotron radiation powder diffraction, while the compositional aspects are investigated using proton-induced X-ray emission and energy dispersive X-ray spectroscopy. Magnetic measurements reveal the magnetic parameters of interest (coercivity, remanence, Curie temperature, saturation magnetization), as well as the exchange-coupled two-phase nature of these magnets and provide information that hints at possible spin reorientation transitions in the Mn-containing planes of the L 10 superlattice. Highlights: Formation of L 10 FeMnPt hard-magnetic single-phase directly in the as-cast state. Specific alternating hard/soft nanostructure stable to 600 °C without grain growth. Strongly anisotropic thermal expansion. Soft-to-hard magnetic transition below ambient temperature. Full exchange-coupling (single magnetic phase behavior).