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Magnetic nanostructures revealing the exchange bias (EB) effect have attracted much interest in recent years due to their promising applications in spintronics, magneticsensing and recording devices with various functionalities. In this paper, we report on the perpendicular exchange bias effect in a multilayered thin film composed of [Co/Pd] ferromagnetic multilayers exchange-coupled to an antiferromagnetic IrMn. The film was deposited on a porous anodized titania template. Influences of the films' surface morphology as well as the order of layers deposited on the EB effect were studied. The enhancements of the EB field H-EB (up to 30%) and the coercive field H-C (two times) were achieved in the nanoporous films relative to their continuous film counterparts, which could be attributed to the specific morphology of the porous surfaces., QC 20190328

For the first time, nanoporous Al2O3 templates with smoothed surface relief characterized by flattened interpore areas were used in the fabrication of Co/Pd and Co/Pt multilayers (MLs) with strong perpendicular magnetic anisotropy (PMA). Alternating gradient magnetometry (AGM) revealed perfectly conserved PMA in the Co/Pd and Co/Pt porous MLs (antidot arrays) with a ratio of remanent magnetization (Mr) to saturation magnetization (MS) of about 0.99, anisotropy fields (Ha) of up to 2.6 kOe, and a small deviation angle of 8° between the easy magnetization axis and the normal to the film surface. The sufficient magnetic hardening of the porous MLs with enhanced coercive field HC of up to ∼1.9 kOe for Co/Pd and ∼1.5 kOe for Co/Pt MLs, as compared to the continuous reference samples (∼1.5–2 times), is associated with the pinning of the magnetic moments on the nanopore edges. Application of the Stoner–Wohlfarth model for fitting the experimental M/MS(H) curves yielded clear evidence of the predominantly coherent rotation mechanism of magnetization reversal in the porous films., QC 20171207

The paper reports on the results of structural analysis and magnetometry of granular nanocomposite films FeCoZr-CaF2 irradiated with Xe and Kr ions at different fluences. The observed effect of enhanced perpendicular magnetic anisotropy characterizing pristine films is discussed with respect to the irradiation regimes and structural changes of the films originating from the impact of ions.

The paper presents frequency f and temperature T-p dependences of phase shift angle Theta, admittance sigma and capacitance C-p for the as-deposited and annealed (CoFeZr)(x)(CaF2)((100-x)) nanocomposite films deposited by ion-beam sputtering of a compound target in a mixed argon-oxygen gas atmosphere in vacuum chamber. The studied films presented metallic FeCoZr cores covered with FeCo-based oxide shells embedded into oxygen-free dielectric matrix (fluorite). It was found for the metallic phase content within the range of 52.2 at.% LT = x LT = 84.3 at.% in low-f region that Theta values were negative, while in the high-f region we observed the Theta LT 0 degrees. It was obtained that the f-dependences of capacitance module displayed minimum at the corresponding frequency when the Theta(f) crossed its zero line Theta = 0 degrees. It was also observed that the sigma(T-p) dependence displayed the occurrence of two minima that were related to the values of Theta(1) = 90 degrees (the first minimum) and of Theta(2)= -90 degrees (the second one). Some possible reasons of such behavior of (CoFeZr)(x)(CaF2)((100-x)) nanocomposite films are discussed. (C) 2013 Elsevier B.V. All rights reserved.

The present paper investigates dependencies of DC/AC conductances on metallic-to-dielectric phase ratio x, temperature T and frequency f in granular nanocomposite films containing FeCoZr nanoparticles embedded into oxygen-free CaF2 matrix. The specific admittance/conductance dependences on x/T/f for the studied films around the percolation configuration was found to be in agreement with their phase structure which was strongly dependent on the composition of gas atmosphere at deposition. The character of temperature/frequency dependences of AC/DC conductance indicates the predominance of electron tunneling (hopping) over the barriers between metallic nanoparticles in carrier transport. (C) 2012 Elsevier B. V. All rights reserved.

The relation between nanoscale structure, local atomic order and magnetic properties of (FeCoZr)(x)(CaF2)(100-x) (29 LT = x LT = 73 at. %) granular films is studied as a function of metal/insulator fraction ratio. The films of a thickness of 1-6 mu m were deposited on Al-foils and glass-ceramic substrates, by ion sputtering of targets of different metal/insulator contents. Structural characterization with X-ray and electron diffraction as well as transmission electron microscopy revealed that the films are composed of isolated nanocrystalline bcc alpha-FeCo(Zr) alloy and insulating fcc CaF2 matrix. They grow in a columnar structure, where elongated metallic nanograins are arranged on top of each other within the columns almost normal to the substrate surface. Mossbauer spectroscopy and magnetometry results indicate that their easy magnetization axes are oriented at an angle of 65 degrees-74 degrees to the surface in films with x between 46 and 74, above the electrical percolation threshold, which is attributed to the growth-induced shape anisotropy. Interatomic distances characteristic for metallic state of alpha-FeCo(Zr) nanograins were revealed by X-ray Absorption Spectroscopy. The results show a lack of surface oxidation of the alloy nanograins, so the growth-induced orientation of nanograins in the films cannot be attributed to this effect. The study is among the first to report a growth-induced non-planar magnetic anisotropy in metal/insulator granular films above the percolation threshold and to reveal the origin of it. (C) 2014 AIP Publishing LLC.

The paper summarizes features in magnetic states of nanocomposite films like superparamagnetic relaxation, exchange interactions, enhanced magnetic anisotropy, originating from their granular nanostructure and related to various combinations of metallic (FeCo(Zr) alloy) nanoparticles and insulating (Al2O3, PbZrTiO3, CaF2) matrix as well as films deposition regimes.

Temperature and magnetic field dependences of electrical conductivity are systematically studied in granular films (Fe45Co45Zr10)(x)(Al2O3)(100-x) (28 LT = x LT = 64) containing crystalline metallic alpha-FeCo-based nanoalloy cores encapsulated in an amorphous oxide shell embedded in an amorphous Al2O3 matrix. Formation of metallic core-oxide shell nanogranules is confirmed by transmission electron microscopy (TEM) and HRTEM. The structure of core and shell is governed with the difference in the oxidation states of Fe and Co ions investigated with EXAFS, XANES and Mossbauer spectroscopy. A considerable negative magnetoresistance (MR) effect of spin-dependent nature is observed in the whole range of x values. Its increase with decreasing temperature is correlated with the magnetic saturation of superparamagnetic metallic nanogranules. The enhanced MR effect in core-shell granular films is related to the percolation of oxide shells and their influence through spin filtering processes. A considerable high field MR at low temperatures and the resulting deviation of MR and squared magnetization are attributed to a magnetic randomness and/or strong magnetic anisotropy of the magnetic oxide shell.