Magnetic properties of Sn-substituted Ni-Zn ferrites synthesized from nano-sized powders of NiO,ZnO, Fe_2O_3, and SnO_2

A series of Ni_(0.6-x/2)Zn_(0.4-x/2)Sn_xFe_2O_4(x = 0.0, 0.05, 0.1, 0.15, 0.2, and 0.3)(NZSFO) ferrite composities have been synthesized from nano powders using a standard solid state reaction technique. The spinel cubic structure of the investigated samples has been confirmed by x-ray diffraction(XRD). The magnetic properties such as saturation magnetization(M_s),remanent magnetization(M_r), coercive field(H_c), and Bohr magneton(μ) are calculated from the hysteresis loops. The value of M_s is found to decrease with increasing Sn content in the samples. This change is successfully explained by the variation of A-B interaction strength due to Sn substitution in different sites. The compositional stability and quality of the prepared ferrite composites have also been endorsed by the fairly constant initial permeability(μ') over a wide range of frequency. The decreasing trend of μ' with increasing Sn content has been observed. Curie temperature TChas been found to increase with the increase in Sn content. A wide spread frequency utility zone indicates that the NZSFO can be considered as a good candidate for use in broadband pulse transformers and wide band read-write heads for video recording. The composition of x = 0.05 shows unusual results and the possible reason is also mentioned with the established formalism.     

Phase transition of nano-sized amorphous tungsten to a crystalline state

We study thermal-physical characteristics of nano-sized amorphous tungsten and of its oxide. It is shown that a nano-size amorphous metal gets into a nano-size crystalline state after heating up to temperatures much lower than the half-temperature of melting, which is typical for all nano-size amorphous materials. Phase transition of amorphous nano-size WO₂ into crystalline state occurs in the temperature range 350–520°C, while the same transition in case of W takes place in the range 1000–1370°C. The energy released at crystallization of nano-size amorphous metal amounts to 170±25 J/g coinciding practically with the value of specific melting heat of usual tungsten. Such a high additional energy of nano-size amorphous metals above the energy of nano-size crystalline metals is their main peculiarity which widens essentially the range of their practical applications.     

Synthesis and thermal transformations of zinc-substituted magnetites

In the present study, zinc-substituted magnetites of the Fe_3???X Zn _X O₄ type were prepared by co-precipitation in the range 0 ≤?X?≤ 1 and, further, annealed in free atmosphere, at 800° for 3 h. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy. The results showed that the annealed samples were oxidized and converted into Fe₂O₃ and ZnFe₂O₄, in relative amounts that varied with X.     

Magnetic properties of aerosol synthesized iron oxide particles

Fine iron oxide particles have been prepared by an aerosol technique. The particles are spherical with a mean size of 0.1 μm. Heat treatment in air or nitrogen at various temperatures for various times leads to a variety of phase mixtures of -Fe₂O₃, γ-Fe₂O₃ and Fe₃O₄. The magnetic properties of these various samples are presented.     

Magnetic properties of transition metal superlattices

The magnetic coupling between Fe layers separated by spacer layers consisting of up to two atomic planes of 3d transition metal elements (Sc, Ti, V, Cr, Fe, Co, Ni and Cu) has been studied systematically by using two complimentary theories based on cluster and band structure methods. The Fe layers are found to be ferromagnetically coupled in all cases except for Cr where this coupling alternates from ferro- to anti-ferromagnetic depending on whether the spacer layers are odd or even. Furthermore the spacer layers involving Sc, Ti and V are anti-ferromagnetically coupled to Fe while Co and Ni layers are coupled ferromagnetically.     

Magnetic properties of ferrites synthesized by low temperature technique

Spinel ferrites have attracted a great deal of attention due to their application potential. These ferrites are attractive as well as from the theoretical point of view. Magnetic properties of the bulk materials differ drastically from the nano-sized materials. Often high temperature sintering is used to synthesize the nano-sized materials via solid state reaction route. This method yields bulk ferrites. For nano-sized materials low temperature sintering is required as basic requirement. Copper zinc ferrites have been synthesized by hydrothermal process which employs the decomposition of the hydroxides precursor at about 100°C. These samples were characterized by X-ray diffractometer (XRD), vibrating sample magnetometer (VSM),electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. The average particle size in these sintered samples measured by XRD is found to vary from 10 to 150 nm. The XRD shows the formation of single phase spinel structure in all the samples. EPR gives the single asymmetric line at g ~ 2 with a line width of several hundred gauss. VSM displays non-saturating hysteresis loops and Mössbauer spectra show two sets of sextet related to two distinct sites of iron: site-A and site-B.     

Magnetic properties and morphology of Ni nanoparticles synthesized in gas phase

We report on the size, structure and magnetic properties of Ni nanoparticles fabricated with a free-jet sputtering nanoparticle source. It is found how the pressure of the inert gas and the diameter of the source nozzle can control the particle size and coercivity in a wide range. Measurements of the specific magnetic moment of Ni nanoparticles are reported. A particular growing regime is found at high pressures over 1.8 mbar observing a further aggregation process that leads to nanoparticle agglomerates with diameters larger than 100 nm with a low dispersion in size.     

Magnetic properties of transition metal substituted MnP

The magnetic properties of polycrystalline samples of Mn_1?tT_tP (T = V, Cr, Fe and Co for 0.00 ≦ t ≦ 0.50) are studied by magnetic susceptibility, magnetization and neutron diffraction measurements. The magnetic phase diagrams of the Mn_1?tT_tP phases exhibit paramagnetic, ferromagnetic, helimagnetic and spin glass regions depending on temperature and substitution (T, t). The concentrated spin glass regions observed in Mn_1?tV_tP and Mn_1?tCo_tP (0.30 ≦ t ≦ 0.50) are believed to result from the disorder in the metal sublattice. The variation of the magnetic moment of the ordered Mn_1?tT_tP phases with the substitution (T, t) is discussed.     

Magnetic phases of amorphous transition metal-metalloid alloys

Hysteresis loop and ac susceptibility measurements were performed on three series of amorphous alloys: (A_wB_1-w)₇₅P₁₆B₆Al₃, where (A, B) are (Fe, Ni), (Co, Ni) and (Fe, Mn). Upon cooling, low w alloys undergo paramagne t to spin glass transitions. Alloys with higher w first experience a Curie transition to a ferromagnetic state, and then a spin freezing transition to a spin glass state. the T dependence of the width of the ac hysteresis loop is used to determine the spin freezing transition temperature. A magnetic phase diagram is presented for each alloy series and the value of w required for ferromagnetism, w_C, is determined. When measured in the presence of small constant fields, the ac susceptibility of alloys with w just above w_C has maxima near both transition temperatures. The field and temperature dependences of the peaks are explained by scaling arguments, used to determine the critical exponent δ for the Curie transition, and suggest that a similar scaling law holds for the ferromagnet to spin glass transition.     

Magnetic anisotropy of deposited transition metal clusters

We present results of magnetic torque calculations using the fully relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one can derive amongst others the magnetic anisotropy energy (MAE). It was found that this approach is numerically much more stable and also computationally less demanding than using the magnetic force theorem that allows to calculate the MAE directly. Although structural relaxation effects were not included our results correspond reasonably well to recent experimental data.     

Structural, magnetic and hyperfine characterization of zinc-substituted magnetites

Nanosized Fe_3???x Zn _x O₄ powders were synthesized by co-precipitation and characterized by total chemical analysis, X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy. The results showed that, for x?≤?0.15, the as-prepared samples are mostly zinc-substituted magnetites but have maghemite as a minor phase. For x?≥?0.30, only the Fe_3???x Zn _x O₄ solid solution is found. Increasing the zinc content from the end concentration x?=?0, increases the lattice parameter but smaller become the mean crystalline diameter and the magnetic susceptibility. In addition, the magnetic hyperfine fields of the iron sites in the spinel structure, A and B, decrease up to collapse at x?≤?0.90.     

Magnetic properties of BiFeO3 micro-cubes synthesized by microwave agitation

In this article, we present results of field cooled (FC) and zero field cooled (ZFC) magnetization measurements and investigation of aging and memory effect in bismuth ferrite (BFO) multiferroic micro-cubes obtained by means of simple microwave synthesis procedure. It is found that difference between FC and ZFC magnetizations appear at the temperature of freezing of ferromagnetic domain walls. The decay of the magnetic moment versus time described by power-law relation and the absence of memory effect are caused by domain growth mechanism rather than by the spin-glass phase. The negligible value of remnant magnetic moment indicates that BFO compound exhibits low concentration of ferromagnetic domains and can be close to ferromagnetic to spin-glass transition.     

Magnetic response of ferromagnet-superconductor bilayers

Magnetic measurements on a ferromagnet/insulator/superconductor (La_2/3Ca_1/3MnO₃/SrTiO₃/YBa₂Cu₃O_7−x) structures were performed with the field applied parallel to the plane of the film. We observed an evidence of a modification of the ferromagnetic domain structure in the magnetic layer induced by the superconducting transition in the neighboring superconducting YBa₂Cu₃O_7−x layer.     

Magnetic properties of barium ferrite synthesized using a microemulsion mediated process

Ultrafine barium ferrite particles have been synthesized using a microemulsion mediated process. The aqueous cores (typically 10–25 nm in size) of water-in-oil microemulsions were used as constrained microreactors for the precipitation of precursor carbonates of Ba²⁺ and Fe³⁺. These precursors (5–15 nm in size) when heated at 950°C, transformed to the hexagonal ferrite BaFe₁₂O₁₉ as confirmed by X-ray diffraction. This barium ferrite powder had an intrinsic coercivity of 5089 Oe and a saturation magnetization of 60.1 emu/g.     

Magnetic anisotropies of late transition metal atomic clusters

We analyze the impact of the magnetic anisotropy on the geometric structure and magnetic ordering of small atomic clusters of palladium, iridium, platinum, and gold. We have employed a noncollinear implementation of density functional theory where the spin-orbit interaction has been included self-consistently. The size of the clusters ranges from two to five, six, or seven atoms, depending on the element. Our results highlight the relevance of the spin-orbit interaction in the magnetic properties of small atomic clusters made of fourth- and fifth-row elements.     

Magnetic properties of hydrothermally synthesized BiFeO3 nanoparticles

BiFeO₃ nanoparticles with diameters in the range 65–90 nm were prepared using a hydrothermal technique. Low-temperature magnetic measurements showed ferromagnetic behavior of the samples below a certain temperature. The magnetization values were drastically reduced in the case of samples having larger diameters. This was explained as arising due to a reduction of the number of uncompensated spins associated with Fe³⁺ ions as particle diameter was increased. A surface spin disorder is believed to be responsible for this property.     

Magnetic surface anisotropy of transition metal ultrathin films

In order to study the magnetic anisotropy of transition metal ultrathin films, we have performed tight-binding calculations including spin-orbit coupling. Beside the anisotropy energy these calculations also yield the orbital moment, which turns out to be much more anisotropic than in bulk materials. The effects of interfacial mismatch and roughness are discussed within phenomenological models. We also briefly review experimental results on the magnetic surface anisotropy (MSA) in transition metal ultrathin films. In some cases such as Au/Co/Au(111) sandwiches the MSA wins the competition with the shape anisotropy arising from the magnetostatic energy: below a critical thickness this leads to aperpendicular spontaneous magnetization. We show the effects of this crossover on the hysteresis loops and on the magnetoresistance, and the effects of interface roughness on the critical thickness.