The Sm-Fe-V based 1:12 bulk magnets

International audienceA bulk magnet based on Sm-Fe-V with the ThMn12 crystal structure has been fabricated for the first time by hot-compaction of mechanically milled powders with a density of 92% of the theoretical density. The isotropic magnet exhibits a maximum coercivity of 1.06 T with a magnetization of 0.59 T, a remanent magnetization of 0.42 T and a (BH)max of 28 kJ m−3 at 3 T applied field. The Curie temperature is found to be 330 °C and the temperature coefficients of remanent magnetization and coercivity are 0.14% C−1 and 0.39% C−1, respectively. Minor hysteresis loops indicate a coercivity mechanism similar to that of the nanocrystalline Nd-Fe-B magnets. The isotropic magnet was hot-deformed up to 75% of its height, and the best magnetic properties obtained were μ0M3T = 0.63 T, μ0Mr = 0.45 T, μ0Hc = 0.88 T and (BH)max = 33 kJ m−3. A small texture perpendicular to compaction direction was detected when the amount of vanadium was reduced, and the deformation temperature was increased from 800 to 1000 °C

Intrinsic magnetic properties of SmFe12−xVx alloys with reduced V-concentration

International audienceIn this work, we present experimental and theoretical results on SmFe 12−x V x (x = 0.5-2.0) alloys with the ThMn 12 (1:12) structure as possible candidates for rare earth-lean permanent magnets. The compound with x = 2 has been previously reported to have a Curie temperature of 330 • C, saturation magnetization of about 80 Am 2 /kg, and anisotropy field around 9 T. We have synthesized the SmFe 11 V compound with a nearly pure 1:12 phase; the x = 0.5 compound couldn't be synthesized. The stability of the x = 1 compound was also confirmed theoretically by calculations of their formation enthalpies using first principles. The newly synthesized SmFe 11 V compound has a Curie temperature of 361 • C and saturation magnetization of 115 Am 2 /kg (1.12 T). The anisotropy field has been obtained in magnetically-oriented fine powders, and is around 11 T. These parameters make SmFe 11 V a good candidate for a new kind of high energy, rare earth-lean permanent magnets

Denitrogenation process in ThMn12 nitride by in situ neutron powder diffraction

ThMn12 nitrides are good candidates for high performance permanent magnets. However, one of the remaining challenges is to transfer the good properties of the powder into a useful bulk magnet. Thus, understanding the denitrogenation process of this phase is of key importance. In this study, we investigate the magnetic and structural stability of the (Nd0.75, Pr0.25)1.2Fe10.5Mo1.5Nx compound (x=0 and 0.85) as function of temperature by means of neutron powder diffraction. Thermal dependence of the lattice parameters, formation of a-(Fe, Mo), as well as the nitrogen content in the nitrides are investigated by heating the compounds up to 1010 K. The decomposition takes place mainly via the formation of the a-(Fe, Mo) phase, which starts at around 900 K, whereas the nitrogen remains stable in the lattice. Additionally, we show that the magnetic properties of the nitrides [M(4T)=90 Am2/kg and Hc=0.55 T] are maintained after the thermal treatments up to 900 K. This study demonstrates that the ThMn12 nitrides with the Mo stabilizing element offer good prospects for a bulk magnet provided an adequate processing route is found

MAGNETIC PROPERTIES OF MELT-SPUN AND SINTERED Fe-Nd-B MAGNETS AT ELEVATED TEMPERATURES

Les propriétés magnétiques d'aimants Nd-Fe-B préparés par trempe sur rouleau et frittés ont été mesurés entre 20 et 350°C. La coercitivité de tous les échantillons décroit très rapidement lorsque la température augmente et devient extrêmement faible à des températures bien inférieures à la température de Curie qui est proche de 300°C. La variation thermique de l'aimantation M sous champ, en températures croissantes et décroissantes, a été étudiée. Elle correspond au comportement de la courbe de première aimantation ainsi qu'à la dépendance en champ de coercitivité.The magnetic properties of melt-spun and sintered Fe-Nd-B magnets have been measured in the temperature range of 20 - 350°C. The coercivity of all samples decreases drastically with increasing temperature and is very small at temperatures considerably lower than the Curie temperature which is around 300°C. The effects of temperature on magnetization during the heating and cooling cycles of the M vs T experiment have been studied and found to be consistent with the initial magnetization behavior and field dependence of coercivity

Fundamental and magnetic-hardening studies of nanocrystalline and nanocomposite magnets. Final technical report

In this project the authors study new nanocrystalline and nanocomposite structures that have high potential for permanent-magnet development. These materials, which can be synthesized to have either very high or intermediate coercivities, have many applications in electric power, transportation, and information-storage industries. There is great interest in further development of understanding and application of these materials. Brief discussions are given for the following research highlights: (A) Fundamental electronic, magnetic and micromagnetic studies; (B) Intrinsic and magnet hardening studies of carbides and alloys; and (C) Nanostructured and nanocomposite films

LOW-FIELD MAGNETIC PROPERTIES OF Fe-Nd-BASED PERMANENT MAGNETS

Des mesures thermomagnétiques en courant continu (champ appliqué : ~ 5 Oe) sur des aimants permanents Fe-Nd-B commerciaux aussi bien que sur des alliages rapidement refroidis sont présentés pour illustrer quelques proprietés magnetiques caractéristiques à des températures comprises entre 30 et 900°C. Des études préliminaires de Spectroscopie Electronique Auger (AES) sur 1'homogénéité de composition et sur les effets d'oxydation pendant le chauffage des aimants commerciaux, surtout Neomax, sont égalment présentées.Low field (in applied fields ~ 5 Oe), dc-thermomagnetic measurements on Fe-Nd-B based technical permanent magnets as well as rapidly quenched alloys are presented to elucidate the salient features of their magnetic properties in the temperature range 30 to 900°C. From Auger Electron Spectroscopic (AES) analyses preliminary studies on the compositional homogeniety as well as the effects of oxidation during the heating of these commercial magnets, Neomax in particular , are also presented

Patterned magnetic thin films for ultra high density recording

The areal bit density of magnetic disk recording has increased since 1990 60% per year and even in the last years 100%. Extrapolation of these rates leads to recording parameters not likely to be achieved without changes in the present way of storing hard disk data. One of the possible solutions is the development of so-called patterned magnetic media. Such media will also shift the superparamagnetic limit positively in comparison with the present thin film media. Theoretically, a bit density in the order of Tbits/in 2 may be possible by using this so-called discrete magnetic recording scheme. The patterned structures presented in this paper consist of a regular two-dimensional array of single domain dots with large uniaxial magnetic anisotropy and have been prepared from CoNi/Pt multilayers with strong intergranular exchange coupling and large perpendicular magnetic anisotropy. For the preparation of the patterned media, a patterning process based on Laser Interference Lithography method (LIL) and Ion Beam Etching has been developed. This technology provides the possibility to pattern 2-D arrays of submicron dots smaller than the critical size for the transition from multi to single domain. The smallest prepared dot sizes are 60 nm with a center-to-center dot spacing of 200 nm and thickness of 30 nm. The magnetic characterization of these dots showed that they are single domain with reasonable coercivity and good thermal stability. Micromagnetic simulations show that the single domain state is the lowest energy state for dots with a diameter below 75nm, which confirms the experimental observations

A new concept in magnetic force microscope cantilevers

In this paper, a new design of dedicated magnetic force microscope (MFM) cantilever is presented. In this design, the cantilever and the magnetic tip are realized in an integrated manufacturing process. The use of silicon micromachining techniques enables batch fabrication of several hundred cantilevers on a single Si wafer. The magnetic tip is prepared by deposition of magnetic material on a free standing silicon nitride layer. The width and thickness of the magnetic tip are defined by the thickness of the silicon nitride layer and the magnetic layer respectively. The length of the tip is lithographically defined. This enables us to realize very thin, high aspect ratio magnetic tips with excellent control over the tip dimensions