AC hopping conductance in nanocomposite films with ferromagnetic alloy nanoparticles in a PbZrTiO3 matrix

In this work, the temperature and frequency dependences of the real part of the admittance of annealed nanocomposite films containing Co45Fe45Zr10-based nanoparticles covered with native oxides and embedded in a doped PbZrTiO3 ferroelectric matrix were studied. The nanocomposites studied were deposited by ion sputtering a complex target in a mixed Ar/O2 atmosphere followed by a 15-min annealing process (with steps of 25 K) in air in the temperature range of 398 K < Ta < 573 K. The conductivity of the annealed samples was measured in the temperature range of 77 K< Tp < 373 K at frequencies of 50 Hz< f< 1 MHz. The observed r(f, T) dependences confirmed that the annealed samples displayed the effects of negative capacitance over the whole frequency and temperature ranges studied because of the pronounced oxidation of the nanoparticles. The r(f, T) dependences obtained are described using an earlier-developed AC hopping conductance model. Comparisons between experimental and simulation results allow the model parameters to be estimated, such as the activation energies of the hopping conductance and the lifetimes of the electrons in the nanoparticles

Spin-Dependent Electronic Transport in IrMn–Co/Pd Multilayered Systems

Relation between magnetoresistance and magnetization reversal in thin multilayered IrMn-Co/Pd films deposited both on planar and nanoporous substrates is in focus of the present work. Magnetic anisotropy, exchange coupling and mechanisms of magnetic resistivity are discussed

Enhanced Perpendicular Exchange Bias in Co/Pd Antidot Arrays

Magnetic nanostructures revealing the exchange bias (EB) effect have attracted much interest in recent years due to their promising applications in spintronics, magnetic sensing 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 HEB (up to 30%) and the coercive field HC (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

CVD graphene sheets electrochemically decorated with “core-shell” Co/CoO nanoparticles

The paper reports on the first successful fabrication of Co-graphene composites by electrochemical deposition of Co nanoparticles (NPs) on the sheets of twisted graphene. Characterization of the surface morphology and element mapping of twisted graphene decorated with Co NPs by transmission and scanning electron microscopy in combination with the energy-dispersive X-ray spectroscopy reveals the formation of isolated quasi-spherical oxidized Co NPs with the mean diameter h di _ 220 nm and core-shell structure. X-ray photoelectron spectroscopy indicates that the core of deposited NPs consists of metal Co while the shell is CoO. Composite Co-graphene samples containing core-shell NPs reveal an exchange bias field up to 160 Oe at 4 K as detected by vibrating sample magnetometry after the field cooling procedure

Ion Irradiation of Oxidized FeCoZr-CaF₂ Nanocomposite Films for Perpendicular Magnetic Anisotropy Enhancement

The paper is focused on the results of Xe ions irradiation of nanocomposite FeCoZr-CaF₂ films synthesized in the oxygen-containing atmosphere. Combined influence of nanoparticles partial oxidation and ion irradiation with different fluences on the crystalline structure, phase composition and magnetic anisotropy is analysed by X-ray diffraction, the Mössbauer spectroscopy and vibrating sample magnetometry. The origin of the detected progressive enhancement of perpendicular magnetic anisotropy as the result of films oxidation and irradiation is discussed in the context of formation of nanoparticles oxide shells and ion tracks along the films normal

Growth-induced non-planar magnetic anisotropy in FeCoZr-CaF2 nanogranular films: Structural and magnetic characterization

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

Correlated evolution of surface morphology, structure and magnetic properties of nanoporous Co/Pd films with perpendicular magnetic anisotropy

In this study, we consider the technological route to conserve perpendicular magnetic anisotropy in porous Co/Pd multilayer thin films deposited over porous anodized templates of TiO2 and Al2O3 with smoothed surface morphology. It is proved that these templates with large contribution on flat-surface interpore areas promote conservation of high magnetic anisotropy constants Keff up to 1.9×106 erg/cm3) and Mr/MS (up to 0.99) as well as magnetic hardening with twice increase of the coercive force HC (up to 2.7 kOe) indicating an excellent potential of the fabricated materials for various magnetic and spintronic devices

Ion-Induced Modification of Structure and Magnetic Anisotropy in Granular FeCoZr-CaF2 Nanocomposite Films

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.10th International Conference on Ion Implantation and other Applications of Ions and Electrons (ION), Jun 23-26, 2014, Maria Curie Skodowska Univ, Kazimierz Dolny, Polan

Enhancement of negative capacitance effect in (CoFeZr)(x)(CaF2)((100-x)) nanocomposite films deposited by ion beam sputtering in argon and oxygen atmosphere

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.International Symposium on Metastable, Amorphous and Nanostructured Materials (ISMANAM), Jun 30-Jul 05, 2013, Torino, Ital

Enhancement of negative capacitance effect in (CoFeZr)x(CaF2)(100-x) nanocomposite films deposited by ion beam sputtering in argon and oxygen atmosphere

The paper presents frequency f and temperature Tp dependences of phase shift angle teta, admittance sigma and capacitance Cp 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.% < x < 84.3 at.% in low-f region that H values were negative, while in the high-f region we observed the teta < 0. It was obtained that the f-dependences of capacitance module displayed minimum at the corresponding frequency when the teta(f) crossed its zero line teta = 0. It was also observed that the sigma(Tp) dependence displayed the occurrence of two minima that were related to the values of teta1 = 90 (the first minimum) and of teta2 = 90 (the second one). Some possible reasons of such behavior of (CoFeZr)x(CaF2)(100-x) nanocomposite films are discussed