Fabrication and magnetic properties of hard/soft magnetostatically coupled FePt/FeNi multilayer microwires

3 pages, 5 figures.-- PACS: 75.70.Cn; 75.60.Ej; 75.50.Ww; 81.15.Pq; 68.65.Ac; 81.40.EfA family of multilayer microwires with hard/soft biphase magnetic behavior is here introduced. The microwires consist of a Fe63Pt27Si10 hard magnetic nucleus and a Fe20Ni80 soft outer shell separated by an intermediate insulating Pyrex glass microtube. The precursor FePtSi glass-coated microwire is fabricated by quenching and drawing technique, and its L10 hard magnetic phase is grown by postannealing treatment technique. The polycrystalline FeNi soft magnetic outer shell has been deposited by electroplating. The analysis of the low-field hysteresis loops of the FeNi soft phase after premagnetizing until near magnetic saturation provides information about the magnetostatic coupling between phases. The FeNi magnetization curve is shifted toward positive field when the FePt remanent magnetization is positive and vice versa. A systematic analysis of the magnetostatic coupling and the corresponding bias field arising from uncompensated poles of the premagnetized FePt hard phase has been performed. The strength of the bias field is shown to increase with the reduction of thickness of the FeNi layer. These magnetostatically coupled biphase systems are thought to be of large potential interest as sensing elements in sensor devices.The work has been developed under the Project No. MAT2004-00150 supported by the Spanish Ministry of Education and Science, MEC. J. T. acknowledges a FPU program fellowship from MEC.Peer reviewe

Local magnetization profile and geometry magnetization effects in microwires as determined by magneto-optical Kerr effect

The local magnetization profile along the length in magnetostrictive Fe-based magnetic microwires has been determined by magneto-optical Kerr effect. The study has been performed in microwires with different geometrical dimensions (i.e., diameter and length). The profiles of remanent magnetization and coercivity remain constant at the middle part for all microwires, whereas significant reduction of net magnetization accompanied by significant change of coercivity is observed when approaching their ends. This local region extends just few tens of micrometer for thin (around 1 μm diameter) wires and up to several hundreds of micrometer for thick (around 10 μm diameter) wires. That predicts that critical length to observe bistability goes from 50 μm to nearly 1 mm as diameter increases from 1 to 10 μm. Results are further interpreted considering the local distribution of magnetic charges at the ends which, arising to reduce stray fields, lead in some cases to inverted loops. © 2013 American Institute of Physics.Jingfan Ye acknowledges the support of the German DAAD under the programme “Research Internships in Science and Engineering (RISE-2011).” The work has been supported by the Spanish Ministry of Economy and Competitiviness under projects PLE2009-0057 and MAT2010-20798-C05-01.Peer Reviewe

Distinguishing nanowire and nanotube formation by the deposition current transients

AbstractHigh aspect ratio Ni nanowires (NWs) and nanotubes (NTs) were electrodeposited inside ordered arrays of self-assembled pores (approximately 50 nm in diameter and approximately 50 μm in length) in anodic alumina templates by a potentiostatic method. The current transients monitored during each process allowed us to distinguish between NW and NT formation. The depositions were long enough for the deposited metal to reach the top of the template and form a continuous Ni film. The overfilling process was found to occur in two steps when depositing NWs and in a single step in the case of NTs. A comparative study of the morphological, structural, and magnetic properties of the Ni NWs and NTs was performed using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry, respectively.M. P. Proença and C. T. Sousa are thankful to FCT for the doctoral and postdoctoral grants SFRH/BD/43440/2008 and SFRH/BPD/82010/2011, respectively. J. Ventura acknowledges the financial support through FSE/POPH. M Vázquez thanks the Spanish Ministry of Economia y Competitividad, MEC, under project MAT2010-20798-C05-01. J. P. Araújo also thanks the Fundação Gulbenkian for its financial support within the ‘Programa Gulbenkian de Estímulo à Investigação Científica’. The authors acknowledge the funding from FCT through the Associated Laboratory - IN and project PTDC/FIS/105416/2008.Peer Reviewe

Determination of closure domain penetration in electrodeposited microtubes by combined magnetic force microscopy and giant magneto-impedance techniques

The domain structure of electrodeposited Co90P10 microtubes exhibiting radial magnetic anisotropy and giant magneto-impedance effect has been characterized by combined magnetic force microscopy imaging and impedance measurements. It has been shown that the size of the closure domains increases with the CoP layer thickness. Furthermore, the depth of the closure domains has been quantitatively determined from the high frequency behavior.The authors want to thank Professor J. Miltat for helpful discussions. This work has been performed under Project No. CAM/07N/0033/1998. A. Asenjo would like to thank the CAM (Spain) for the postdoctoral fellowship. J. P. Sinnecker thanks the Brazilian agencies CNPq and FAPERJ for the financial support.Peer reviewe

Plasmon-enhanced magneto-optical activity in ferromagnetic membranes

Experimental and theoretical evidence of plasmon-enhanced Kerr rotation in purely ferromagnetic membranes with sufficiently small dimensions to be out of extraordinary optical transmission conditions (45 nm pore diameter, 90nm lattice constant), is reported in this work. It is shown that the spectral location of the enhanced Kerr rotation region varies as the refractive index of the material inside the pore is modified. A similar behavior is obtained if the pore radius changes while keeping the pore concentration unchanged. Those are clear signatures indicating that localized surface plasmon resonances propagating along the pores govern the magneto-optical response of the membraneWe acknowledge Spanish MICINN (Grant Nos. MAT2008-06765-C02-01/NAN, CSD2008-00023, and MAT2007-65420-C02-01), CSIC (Grant No. PIF 200560F0121 BIOPTOMAG), CM(Grant No. S-0505/MAT/0194 NANOMAGNET), and European Commission (Grant No. NMP3-SL-2008-214107-Nanomagma) for financial support.Peer reviewe

Magnetic hardening of Fe30Co70nanowires

3d transition metal-based magnetic nanowires (NWs) are currently considered as potential candidates for alternative rare-earth-free alloys as novel permanent magnets. Here, we report on the magnetic hardening of FeConanowires in anodic aluminium oxide templates with diameters of 20 nm and 40 nm (length 6 μm and 7.5 μm, respectively) by means of magnetic pinning at the tips of the NWs. We observe that a 3-4 nm naturally formed ferrimagnetic FeCo oxide layer covering the tip of the FeCo NW increases the coercive field by 20%, indicating that domain wall nucleation starts at the tip of the magnetic NW. Ferromagnetic resonance (FMR) measurements were used to quantify the magnetic uniaxial anisotropy energy of the samples. Micromagnetic simulations support our experimental findings, showing that the increase of the coercive field can be achieved by controlling domain wall nucleation using magnetic materials with antiferromagnetic exchange coupling, i.e. antiferromagnets or ferrimagnets, as a capping layer at the nanowire tips.We acknowledge funding from the European Community's Seventh Framework Programme (FP7-NMP) under grant agreement no. 280670 (REFREEPERMAG)

Novel magnetic nanostructures: nanopillars and patterned antidots

Resumen del trabajo presentado en el Simposio Nuevas fronteras y retos en Magnetismo de la XXXVIII Reunión Bienal de la Real Sociedad Española de Física, celebrada en Murcia (España), del 11 al 15 de julio de 2022Two different nanostructures are studied in this contribution: large-area nanopillar arrays fabricated by glancing angle deposition with magnetron sputtering (MS-GLAD) and magnetic thin films perforated with long-range order arrays of nanoholes prepared by focused ion beam (patterned antidots). MS-GLAD is an easy and versatile route to fabricate arrays of nanostructures in large areas in a single processing step. In our work, nanostructured films with vertical or tilted nanopillars composed by polycrystalline Fe and Fe2O3 have been fabricated depending on whether the substrate is kept rotating azimuthally during deposition or not, respectively [1]. The magnetic properties of these films can be tuned with the specific morphology. In particular, the growth performed through a collimator mask mounted onto a not rotating azimuthally substrate produces almost isolated well-defined tilted nanopillars that exhibit a magnetic hardening. The first-order reversal curves diagrams and micromagnetic simulations revealed that a growth-induced uniaxial anisotropy, associated with an anisotropic surface morphology produced by the GLAD in the direction perpendicular to the atomic flux, plays an important role in the observed magnetic signatures. Magnetic antidots are being studied for different applications, such as magnonic crystals for microwave devices, magnetically-active plasmonic media, magnetic biosensing, and magneto-resistance sensors. In our work, a top-down approach using focused ion beam has been employed to fabricate Co/Permalloy hard-soft bilayer antidot arrays [2]. The antidots have a 40 nm diameter and two symmetries are studied: square and hexagonal. A dependence of magnetic coercivity on the relative thicknesses of the magnetically hard (Co) and soft (Permalloy) layers is found; increasing Permalloy thickness results in lower magnetic coercivity. Furthermore, the long-range periodicity of these antidots results in higher magnetic coercivity and a stronger magnetic domain-wall pinning, compared to identical hard/soft bilayers of short-range order deposited on porous anodic alumina. Finally, magnetic force microscopy (MFM) imaging of the antidot arrays shows striking qualitative differences between the two symmetries: square symmetry arrays have inhomogeneous magnetic state and a high density of immobile super-domain walls, whereas hexagonal symmetry arrays show a homogeneous magnetic configuration.The service from the MiNa Laboratory at IMN. Funding from MINECO, Comunidad de Madrid, European Union, Fondecyt, Dicyt-Usach, São Paulo Research Foundation, Brazilian National Council for S., NSRF Greece-EU, NATO

Magnetic properties of spinel-type oxides NiMn2-xMexO4

New materials, based on the well-known spinel compound NiMn2O4, have been synthesized and characterized from the magnetic point of view. The manganese cation was partially substituted in the general formula NiMn2-xMexO4 , by nonmagnetic and magnetic elements, such as Me = Ga, Zn, Ni and Cr (0 x 1). Prior to the determination of their magnetic properties, the non-substituted spinel NiMn2O4 was carefully characterized and studied as a function of the oxygen stoichiometry, based on the influence of the annealing atmosphere and quenching rate. The ferrimagnetic character was observed in all samples, with a paramagnetic-to-ferromagnetic transition temperature Tc stabilized at 110 K, and well defined long-range antiferromagnetic interactions at lower temperatures, which depend on the applied field and the substitute concentrationAuthors from Chile and O.P. thank projects Fondecyt-Chile 1020066, 7020066 and 1050178. Authors from France and Brazil thank project CAPES/COFECUB 416/03. Authors from France thank Région Bretagne for financial supportPeer reviewe

Toward Rare-Earth-Free Permanent Magnets: A Combinatorial Approach Exploiting the Possibilities of Modeling, Shape Anisotropy in Elongated Nanoparticles, and Combinatorial Thin-Film Approach

The objective of the rare-earth free permanent magnets (REFREEPM) project is to develop a new generation of high-performance permanent magnets (PMs) without rare earths. Our approach is based on modeling using a combinatorial approach together with micromagnetic modeling and the realization of the modeled systems (I) by using a novel production of high-aspect-ratio (>5) nanostructrures (nanowires, nanorods, and nanoflakes) by exploiting the magnetic shape anisotropy of the constituents that can be produced via chemical nanosynthesis polyol process or electrodeposition, which can be consolidated with novel processes for a new generation of rare-earth free PMs with energy product in the range of 60 kJ/m3 < (BH)max < 160 kJ/m3 at room temperature, and (II) by using a high-throughput thin-film synthesis and high-throughput characterization approach to identify promising candidate materials that can be stabilized in a tetragonal or hexagonal structure by epitaxial growth on selected substrates, under various conditions of pressure, stoichiometry, and temperature. In this article, we report the progress so far in selected phases.This work is supported by European Commission (REFREEPERMAG project) grant number GA-NMP3-SL-2012-280670