Magnetic hardening in rapidly quenched Fe-Pr and Fe-Nd alloys

We report studies of high-field magnetization and thermomagnetic effects in rapidly quenched and heat treated alloys based on Fe-Pr and Fe-Nd. Coercivities up to ~40 kOe and large energy products result from the precipitation of a finely dispersed crystalline phase. Studies of varying the alloy composition and heat treatment are reported. Journal of Applied Physics is copyrighted by The American Institute of Physics

Structural and magnetic properties of Co-V nanoparticles

We have investigated the structural and magnetic properties of Co1-xVx nanoparticles (NPs) with composition x = 0.25 (stoichiometric) and 0.29 (under-stoichiometric) prepared by the cluster-beam deposition (CBD) technique. Our data shows that the as-made Co1-xVx NPs are a mixture of the high-temperature phase (HTP) and the low-temperature phase (LTP) of Co3V and the particles are superparamagnetic at room temperature (RT) with blocking temperatures (TB) of 90 and 137 K for x = 0.25 and 0.29, respectively. This behavior contrasts with the bulk which are paramagnetic down to 4.2 K. When the Co75V25 NPs are annealed at 573 K, they undergo a phase separation into a mixture of phases and become ferromagnetic at room temperature with Curie temperature (Tc) of 515 K

Electron transport in Tb- and Pr-based metallic glasses

Electrical resistivity measurements are reported on several metallic glasses based on Pr and Tb, and Ga and various transition metals as the glass formers. In general negative temperature coefficients were observed and these are discussed in terms of the extended Ziman theory and the tunneling or localization theory. Low temperature structure in the resistivity can be understood with the coherent exchange scattering model of Asomoza et al. Journal of Applied Physics is copyrighted by The American Institute of Physics

Microstructural characterization of L10 FePt/MgO nanoparticles with perpendicular anisotropy

L10 FePt nanoparticles with perpendicular magnetic anisotropy were fabricated on a heated MgO substrate by using an atomic deposition technique. The microstructure of the FePt nanoparticles was studied by transmission electron microscopy and high resolution transmission electron microcopy. The as-made L10 FePt nanoparticles are isolated and have a faceted morphology with a bimodal distribution of particle size as small as 2.5 nm. A semicoherent atomic interface between the FePt nanoparticles and the MgO substrate is observed. The room temperature coercivity of these FePt nanoparticles was measured via both superconducting quantum interference device and magneto-optical Kerr effect techniques and found to be as high as 6.7 kOe

Effect Of Nb And Cu On The Crystallization Behavior Of Understoichiometric Nd–Fe–B Alloys

In this work, we present a complete study of the influence of Nb and Cu addition on the crystallization behavior of Nd-lean Nd-Fe-B melt-spun alloys. Alloys with compositions Nd10-x-yFe84B6NbxCuy (x = 1, y = 0 and x = 0.5, y = 0.5) were melt-spun at different wheel speeds (15-40 m s(-1)) to obtain samples in amorphous, highly disordered and nanocrystalline structures. The crystallization process, induced by different heat treatments, was studied by means of differential thermal analysis and x-ray powder thermodiffraction. Magnetic properties of as-made and heat-treated ribbons were measured by magnetometry. The as-made amorphous samples showed a crystallization to the 2: 14: 1 hard magnetic phase at T-1 similar to 350 degrees C. Doping with Nb results in an increase of T1, and addition of Cu lowers T1. This behavior is explained in terms of an inhibition of grain growth by Nb and a nucleation enhancement by Cu additions. During the crystallization process, a secondary phase (identified as a bcc-Fe-rich phase) is formed. The amount of such a phase increases with the annealing temperature. Coercivity increases upon annealing reaching maxima at 700-750 degrees C. This can be explained in terms of competition between the two phases formed: the 2: 14: 1 hard phase and the soft bcc-Fe-rich phase. The highest coercivity of the Nd-lean samples is observed when the microstructure is appropriate and both phases are exchange-coupled.This work has received funding from the DOE BES-DE-FG02-90ER45413 and the European Union MSCA grant agreement No 691235 (INAPEM). Technical and human support provided by SGIker (UPV/EHU, GV/EJ and ESF) is gratefully acknowledged

Hardness of porous nanocrystalline Co-Ni electrodeposits

The Hall-Petch relationship can fail when the grain size is below a critical value of tens of nanometres. This occurs particularly for coatings having porous surfaces. In this study, electrodeposited nanostructured Co-Ni coatings from four different nickel electroplating baths having grain sizes in the range of 11-23 nm have been investigated. The finest grain size, approximately 11 nm, was obtained from a coating developed from the nickel sulphate bath. The Co-Ni coatings have a mixed face centred cubic and hexagonal close-packed structures with varying surface morphologies and different porosities. A cluster-pore mixture model has been proposed by considering no contribution from pores to the hardness. As the porosity effect was taken into consideration, the calculated pore-free hardness is in agreement with the ordinary Hall-Petch relationship even when the grain size is reduced to 11 nm for the Co-Ni coatings with 77±2 at% cobalt. The present model was applied to other porous nanocrystalline coatings, and the Hall-Petch relationship was maintained. © 2013 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht. © KIM and Springer

Nanostructured Melt-Spun Sm(Co,Fe,Zr,B)7:5 Alloys for High-Temperature Magnets

High coercivity, the highest for Cu-free 2 : 17 Sm-Co ribbons, has been obtained in as-spun (= 211 kOe) and short time annealed (= 232 kOe) samples of Sm(CobalFe Zr B)7 5 alloys, with varying B, Zr, and Fe content (= 0-0 06, = 0-0 16, = 0 08-0 3) and wheel speed. In as-spun samples, the TbCu7 type structure and in annealed samples the Th2Zn17 and CaCu5 type structures is observed, plus fcc Co as minority phase is observed. Reduced remanence () is higher than 0.7. High-temperature magnetic measurements show very good stability above 300 C with coercive field as high as 5.2 kOe at 330 C. For annealed Sm(CobalFe0 3Zr0 02B0 04)7 5, very good loop squareness and high maximum energy product of 10.7 MGOe have been obtained. Increasing Zr content results in less uniform microstructure of annealed ribbons.Comment: IEEE Transactions on Magnetics, Vol. 39, No. 5, pages 2869 - 2871, September 200

Applying high‐throughput computational techniques for discovering next‐generation of permanent magnets

The uncertainty in rare‐earth market resulted in worldwide efforts to develop rare‐earth‐lean/free permanent magnets. In this paper, we discuss about this problem and analyse how advances in computational and theoretical condensed matter physics could be essential in the development of a new generation of high‐performance permanent magnets via high‐throughput computational technique for material design. Additionally, we show that an adaptive genetic algorithm based methodology could be a useful tool for finding new magnetic phases. In particular, we apply such approach to Fe0.75Sn0.25 compound recovering well‐known experimental results and also finding new low‐energy magnetic metastable structuresNOVAMAG project, under Grant Agreement No. 686056, EU Horizon 2020 Framework Programme for Research and Innova-tion (2014-2020). Authors also acknowledge the Spanish Super-computing Network (RES) and CESVIMA for providing super-computational resources under Ref. QCM-2016-2-003