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

Nanometer scale hard/soft bilayer magnetic antidots

The effect of arrays of nanometer scale pores on the magnetic properties of thin films has been analyzed. Particularly, we investigated the influence of the out-of-plane magnetization component created by the nanopores on the in-plane magnetic behavior of patterned hard/soft magnetic thin films in antidot morphology. Its influence on the coupling in Co/Py bilayers of few tens of nanometer thick is compared for disordered and ordered antidots of 35-nm diameter. The combination of magneto-optical Kerr effect (MOKE) and first-order reversal curve (FORC) technique allows probing the effects of the induced perpendicular magnetization component on the bilayer magnetic behavior, while magnetic force microscopy (MFM) is used to image it. We found that ordered antidots yield a stronger out-of-plane component than disordered ones, influencing in a similar manner the hard layer global in-plane magnetic behavior if with a thin or without soft layer. However, its influence changes with a thicker soft layer, which may be an indication of a weaker couplingThis work was financially supported by the i-Link project “Magnetic antidots,” funded by Consejo Superior de Investigaciones Científicas (CSIC, Spain) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Brazil). We also acknowledge additional funding from Spain, through MINECO (ref.: MAT2014-59772-C2-1-P), Comunidad de Madrid (ref: Nanofrontmag) and CSIC (ref.: 201460E014), from CAPES Brazilian funding agency, and from the E.C. through a FP7-ICT project (Grant No. 318144). The authors thank Raquel Álvaro (from IMM-CSIC) for the planarization of the initial templates.Peer reviewe

Magnetic structure of nanometer scale magnetic antidot arrays

Trabajo presentado en la conferencia Fuerzas y Túnel (FyT2016), celebrada en Girona del 5 al 7 de septiembre de 2016.Magnetic antidot arrays are groups of ordered holes patterned on a continuous magnetic film. They can be used as magnonic crystals with potential application in microwave devices [1], for magnetically-active plasmonics [2], and for biosensing applications [3]. We have followed two different routes to obtain magnetic antidots on Co, Permalloy (Py), and Co/Py films with different characteristics. Focused ion beam allowed obtaining hexagonal or square lattice antidot arrays with long-range order (hole diameter d=55nm, periodicity p=150-300nm) [4], whereas oblique deposition onto nanoporous alumina templates was used to obtain arrays with only hexagonal short-range order (d=40nm, p=105nm) [5]. The arrays were studied by magneto-optic Kerr effect, magnetic force microscopy (MFM) and micromagnetic simulations. It is shown how the coercivity increases with the density of antidots and the magnetic anisotropy axes strongly depend on the array symmetry. The MFM images show the magnetic structure of the arrays to be commensurate to their morphology, with domain walls (DW) pinned by the holes and in some cases super-DW separating linear domains (see Fig.).Funding from CSIC (i-Link0783), MINECO (MAT2014-59772-C2-1), Comunidad de Madrid (Nanofrontmag), FAPESP (Brazil), Basal and Fondecyt (Chile) and EU (318144 and 272470).N

Investigation of magnetic coupling in FePt/spacer/FePt trilayers and in nanometer scale Cobalt/Permalloy magnetic antidots

Trabajo presentado en el 5th Magnetism Spring Meeting, celebrado en Madrid, el 23 de mayo de 2018Peer reviewe