Mn-Induced Thermal Stability of L10 Phase in Fept Magnetic Nanoscale Ribbons.

Alina Daniela Crisan,Ioan Dan,Dan Pantelica,Aurel Leca,Ovidiu Crisan

doi:10.3390/nano10071278

Abstract

Magnetic nanoscale materials exhibiting the L10 tetragonal phase such as FePt or ternary alloys derived from FePt show most promising magnetic properties as a novel class of rare earth free permanent magnets with high operating temperature. A granular alloy derived from binary FePt with low Pt content and the addition of Mn with the nominal composition Fe57Mn8Pt35 has been synthesized in the shape of melt-spun ribbons and subsequently annealed at 600 °C and 700 °C for promoting the formation of single phase, L10 tetragonal, hard magnetic phase. Proton-induced X-ray emission spectroscopy PIXE has been utilized for checking the compositional effect of Mn addition. Structural properties were analyzed using X-ray diffraction and diffractograms were analyzed using full profile Rietveld-type analysis with MAUD (Materials Analysis Using Diffraction) software. By using temperature-dependent synchrotron X-ray diffraction, the disorder–order phase transformation and the stability of the hard magnetic L10 phase were monitored over a large temperature range (50–800 °C). A large interval of structural stability of the L10 phase was observed and this stability was interpreted in terms of higher ordering of the L10 phase promoted by the Mn addition. It was moreover found that both crystal growth and unit cell expansion are inhibited, up to the highest temperature investigated (800 °C), proving thus that the Mn addition stabilizes the formed L10 structure further. Magnetic hysteresis loops confirmed structural data, revealing a strong coercive field for a sample wherein single phase, hard, magnetic tetragonal L10 exists. These findings open good perspectives for use as nanocomposite, rare earth free magnets, working in extreme operation conditions.

Highlights

There is nowadays a sustained research interest for developing new magnetic materials without rare earth elements (RE), while taking into account the critical raw materials shortage of these materials and their contaminating effects on the environment
By using temperature-dependent synchrotron X-ray diffraction, the disorder–order phase transformation and the stability of the hard magnetic L10 phase were monitored over a large temperature range (50–800 ◦C)
CoInncolurdsieorntso assess the effect of Mn addition on the structural stability of L10 FePt phase, a Fe57Mn8Pt35 granular alloy has been synthesized in the shape of melt-spun ribbons and subsequently anneaIlnedoradte6r00to◦aCssaensds t7h0e0 e◦fCfefcot ropf rMomnoatidndgittihone foonrmthaetiosntruocftusirnagl lestapbhialistey Lo1f0Lt1e0trFaegPotnaplh, ahsaer,da mFae5g7nMenti8cPpt3h5agsrea.nAumlarixaollfouynhcoasnvbeenetniosnyanltahnedsiczleadssiinc cthhearsahcatepreizoaftimoneltte-cshpnuinquriebsbhoanssbaenendesmubpsleoqyuedenfotlry caonmnpeoalseitdioantal6,0s0tru°Cctuarnadl a7n0d0 m°Cagfnoertipcraonmaolytsinisgotfhtehefoarsm-caatsitoanndofansinnegalleedphsaamsepLle1s0. tPertoratogno-ninald,uhcaerdd Xm-raagyneemticispsihoanses.pAecmtroixscoofpuynwcoansveemntpiolonyaeldanindocrladsesrictochaassreascstetrhizeactoiomnptoescihtinoinqauleesffheacstsbienentheemteprlnoayreyd for compositional, structural and magnetic analysis of the as-cast and annealed samples

Summary

Introduction

There is nowadays a sustained research interest for developing new magnetic materials without rare earth elements (RE), while taking into account the critical raw materials shortage of these materials and their contaminating effects on the environment. We have previously shown that Mn addition in small amounts (36 at%) creates better stability of L10 phase, and it promotes the occurrence of both binary FePt and ternary FeMnPt L10 phases, making the alloys highly coercive [6,8]. Manoharan et al [11] studied the magnetic and structural properties of highly ordered epitaxial Fe50−xMnxPt50 thin films and found a significant increase in the coercivity for a Mn content of 12 at%. They attributed the increase in coercivity to the tetragonal distortion, since they obtained a c/a ratio larger than the expected value for ferromagnetically-ordered Mn atoms in the Mn sublattice of the L10 phase. A mix of unconventional characterization methods, such as proton induced X-ray emission (PIXE) and high-temperature synchrotron radiation diffraction (HTSRD), and conventional methods, such as powder X-ray diffraction and SQUID magnetometry, were employed in order to derive the structure and magnetic properties and to prove the structural stability of the L10 phase

Experimental

Results and Discussions

Conclusions