Structure and magnetic properties of nanogranular composites CoFeZr-alumina

The 5 to 15 μm thick nanocomposite films (Coo.45Fe0.45Zr0.10)x(Al2O3)1-x with 30 < x < 65 at.% sputtered in a chamber evacuated with pure Ar gas were studied using Mössbauer spectroscopy, magnetization, complex magnetic permeability, and magneto-force microscopy (MFM) measurements. In particular, the films with x < 40 at.% displayed superparamagnetic state at room temperature (the lack of sextets in Mössbauer specta, non-hysteresis character of the magnetization curves, invariability of real μ’ and imaginary μ’’ parts of magnetic permeabilities with x and high resistivity. Near the percolation threshold ( x ≈ 40 - 45 at.%) Mössbauer specta displayed features of the ferromagnetic sextet and the values of μ’ and μ’’ increased, approaching the maximum, as x increasing due to the decrease of inter-particle distances. Moreover, effects of dipole-dipole and exchange interactions of the nanoparticles resulted in the nucleation of the magneto-ordered granules (magnetoclusters) including a few metallic nanoparticles. The MFM allowed to visualizing the presence of magnetic labyrinth-like magnetic contrast that was formed by the metallic nanoparticles near the percolation threshold. At x > 45 at.% the films behave like the “bulk” ferromagnetic sample with occasional inclusions of dielectric phase. 1. INTRODUCTION At present time high interest is given to granular composite materials, which consist of metallic nanosized particles randomly distributed within a dielectric matrix, because they represent nearly ideal systems for the study of nanostructured materials with a big change of their composition. For the first time, such materials (named as cermets) were manufactured at the beginning of seventies of the last century and during that decade the main concepts concerning the electrical and magnetic properties of composites were stated [1-5]. The interest of these materials was renewed in the nineties, of the previous century, because of their possible applications in the magnetic field sensors and as magnetic recording media. The study of magnetic properties of iron, cobalt or nickel nanoparticles embedded into a dielectric matrix has shown [6] that reduction of volume fraction of the metallic phase below the percolation threshold xC resulted in metallic granules becoming a singledomain and the nanocomposite as a whole displays superparamagnetic properties at room te

Volume One (Birgit Krohn Albums)

The first of Birgit Krohn\u27s three albums containing printed and manuscrip] music, much of which was likely collected during her time at Nikka Vonen\u27s school for girls in Dale, Norway.https://scholarexchange.furman.edu/krohn-album1/1000/thumbnail.jp

Электрические свойства черного мышьяка

R(T, B) of the natural black arsenic (b-As) polycrystal was studied. It was shown that the polycrystalline b-As sample contains the b-As phase and also the traces of its oxide, as well as grey arsenic and arsenolite (As2O3). The behavior of the relative magnetoresistance of the b-As crystal was described by the relation MR(B) = bBn + cBm, where the coefficients b and c and the exponents n and m were also affected by the mechanisms of magnetoresistance formation and temperature. At the temperatures below 10 K, MR(B) shows the presence of a competition between negative (with b &lt; 0 and n ≈ 0.5) and positive (with c &gt; 0 and m ≈ 1) contributions. Above 10 K, only the PMR effect was presented. For the PMR effect, at 10 &lt; T &lt; 100 K it is observed that the values of b &gt; 0, n ≈ 1 and c → 0. Above 100 K, it is observed that the values of b, c &gt; 0 and n ≈ 1 and 1.30 &lt; m &lt; 1.47. The observed behavior of the R(T, B) dependences is associated with strong inhomogeneity and/or disorder of the investigated black arsenic crystal.Исследована структура, а также зависимости электрического сопротивления R(T) от температуры поликристалла природного черного мышьяка (b-As). Образцы b-As содержали как фазу черного мышьяка и следы его окисла, так и фазу серого мышьяка и арсенолита (As2O3). Поведение относительного магнетосопротивления MR(B) кристалла b-As при постоянной температуре описывалось соотношением MR(B) = bBn+ cBm, где коэффициенты b и с, а также показатели степени n и m определялись механизмами формирования магнетосопротивления и зависели от температуры. При температурах ниже 10 К зависимость MR(B) показывает наличие конкуренции отрицательного (при b &lt; 0 и n ≈ 0,5) и положительного (при с &gt; 0 и m ≈ 1) вкладов. При температуре T &gt; 10 К наблюдался только ПМР эффект, для которого в диапазоне 10 &lt; T &lt; 100 К величины b &gt; 0, n ≈ 1 и с → 0. При Т &gt; 100 К величины b, с &gt; 0, n ≈ 1 и 1,30 ≤ m ≤ 1,47. Наблюдаемое поведение зависимостей MR(B) в широком диапазоне температур обусловлено сильной неоднородностью и неупорядоченностью структуры исследуемого кристалла черного мышьяка

Equivalent Circuits for FeCoZr-Al2O3 Nanocomposite Films Deposited in Argon and Argon-Oxygen Atmospheres

The investigation of the equivalent circuits for granular nanocomposite films was performed according to the method of the impedance spectroscopy. The films, consisted of the Fe0.45Co0.45Zr0.10 ferromagnetic alloy nanoparticles embedded into amorphous dielectric alumina matrix, were deposited in pure argon or argon and oxygen mixture. The temperature dependences of active and reactive components in the equivalent circuits for the (Fe0.45Co0.45Zr0.10)x(Al2O3)(1-x) nanocomposite films are compared and analyzed. The presence of the inductive part in the equivalent circuits for the samples deposited in Ar gas below and beyond percolation threshold is shown. It is revealed that the equivalent circuits of the (Fe0.45Co0.45Zr0.10)x(Al2O3)(1-x) nanocomposites produced in argon + oxygen gas mixture show more strong inductive contribution than ones sputtered in pure argon

Gigantic Magnetoresistive Effect in n-SiSiO2Ni Nanostructures Fabricated by the Template-Assisted Electrochemical Deposition

The study of the carrier transport and magnetotransport in n-Si/SiO2/Ni nanostructures with granular Ni nanorods embedded into the pores in SiO2 was performed over the temperature range 2 – 300 K and at the magnetic field induction up to 8 T. In n-Si/SiO2/Ni nanostructures at temperatures of about 25 K a huge positive MR effect is observed. Possible mechanisms of the effect is discussed

Magnetotransport in Nanostructured Ni Films Electrodeposited on Si Substrate

The study of electrical resistivity  and magnetoresistance MR in nanogranular Ni films was performed over the temperature range 2 - 300 K and at the magnetic field induction B up to 8 T. The Ni layers having a thickness of about 500 nm were prepared by electrodeposition on n-Si wafers. According to an X-ray diffraction study, a strongly textured face-centered cubic structure was formed in the as-deposited films with an average grain sizes of about 10 - 70 nm. Experiments have demonstrated that the magnetic field and temperature dependences of the MR effect in Ni films shown two main peculiarities: (1) dependencies on the mutual orientations of vectors B, current and the film plane; (2) two contributions to the MR - negative anisotropic magnetoresistance and positive Lorentz-like MR

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