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Hexagonal Ba(Ti1-xFex)O3-δ (x = 1/6, 1/3) ceramics treated with post annealing are specifically synthesized to explore the origin mechanism of the unusual ferromagnetism in the doped system. X-ray diffraction refinements and transmission electron microscope experiments reveal that their structures are incommensurately modulated owing to simultaneous oxygen vacancies at both O1 and O2 sites. Consequently, coexisting weak ferrielectricity and weak ferromagnetism are presented at room temperature. Analysis on their leakage current plot reveals that their conduction follows trap-filled limit model. In combination with the magnetism studies on 5 mol% Fe-doped crystals [Phys. Rev. B 83, 144407 (2011)], the reduction of ferromagnetism with an increase of conductivity suggests that dynamic exchanges of trapped electrons among the bound magnetic polarons attribute to the intrinsic ferromagnetism. [ABSTRACT FROM AUTHOR]

CoPt hard magnetic films were produced by loading aqueous solution of CoPt mixture salt into PAF and employing hydrogen reduction at elevated temperature. The AFM images reveal that the pores of PAF substrate are partially covered with CoPt particles.

The structure and magnetic properties of multilayer magnets with a hard phase (HP1=Nd13.5Dy1.5Fe68Co10B7 or HP2=Nd14Dy1Fe68Co10B7) and soft phase Fe, prepared by sputtering and subsequent heat treatment, have been investigated. For Si/Ti(20 nm)/[HP1(2.0 nm)/Fe(0.5 nm)]×200/Ti(10 nm) multilayer film, transmission electron microscopy results show that Fe disperses in amorphous NdDyFeCoB alloy. After annealing at 575 °C for 5 min, the hard Nd2Fe14B phase typically with grains of about 50 nm and some amount of α-Fe coexist in the film. The grain size of the hard and soft phases can be controlled by the proper thickness of the layer and the period. A coercivity of 7.7 kOe and a ratio Mr/Ms of 0.74 are achieved in the multilayer Si/Ti(20 nm)/[HP2(2 nm)/Fe(0.5 nm)]×200/Ti(10 nm). A good squareness of the hysteresis loop (measured even at 200 K) is observed, due to the effective exchange coupling between the magnetically soft and hard nanograins in the film. A pinning-type mechanism dominates the magnetization reversal process. In addition, the effect of the effective anisotropy, the grain size, and interfaces between the magnetically hard and soft phases on the exchange coupling is discussed. [ABSTRACT FROM AUTHOR]

A simple synthetic procedure involving the pyrolysis of Fe and Pt acetylacetonates mixed in trioctylamine results in the formation of alloy clusters with an average cluster around 4.2 nm and narrow size distribution. When the clusters are dispersed onto silicon wafers and heated under the protection of forming gas or nitrogen, the fcc structured clusters transform into hard magnetic FePt clusters with L10 chemical order. Coercivity values as high as 23 kOe are reached after rapid thermal annealing at 750 °C for 5 min. [ABSTRACT FROM AUTHOR]

Dy1-xPrx(Fe0.35Co0.55B0.1)2 (0<=x<=1) Laves compounds with a cubic MgCu2-type structure were synthesized by arc melting and subsequent annealing. The lattice parameter of the Laves compounds linearly increases, while the Curie temperature TC decreases with increasing Pr content. The saturation magnetization Ms at 5 K or 295 K for the Dy1-xPrx(Fe0.35Co0.55B0.1)2 alloys decreases to reach a minimum, then increases with increasing Pr content. The composition for magnetic moment compensation is about x=0.55 at 295 K and x=0.65 at 5 K, respectively. The magnetostriction λ∥ or λ⊥ at room temperature was investigated either parallel or perpendicular to the applied field using a standard strain gauge technique. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of multilayer magnets containing a hard phase [HP≡;(Nd0.95Dy0.05)(Fe,Co,Nb,B)5.5] and a soft phase (SP≡Fe and Fe65Co35) have been investigated. For the nanocomposite multilayer of Si(substrate)/Ti(30 nm)/ [HP(x nm)/SP(y nm)]n/Ti(30 nm), the remanence enhancement has been observed at different thickness and volume fractions of hard- and soft-phase layers. The remanence increases and the coercivity decreases with the addition of soft phase, in comparison with the results of the single-layer film. For the multilayer of Si(substrate)/Ti(30 nm)/[HP(15 nm)/Fe(5 nm)]n/Ti(30 nm) annealed at 575 °C for 30 min, the coercivity of the multilayer reaches a maximum at n=20. Effects of the layer thickness and volume fraction of hard- and soft-phase layers on magnetic properties and exchange coupling in the multilayer films have been observed. [ABSTRACT FROM AUTHOR]

FePt L10-structured clusters were synthesized by hydrogen reduction of FesNO3d3.9H2O and H2PtCl6.6H2O mixtures within the pores of alumina. They were released by dissolving the alumina matrix and capped with organic surfactants. After a series of chemical treatments, clusters with an average diameter of about 11 nm were precipitated. The clusters were drop casted onto ordered nanoporous arrays. Clusters reaching the bottom of the pores formed an ordered magnetic array. The corresponding magnetic film exhibits distinct anisotropic behavior caused by the external magnetic field. [ABSTRACT FROM AUTHOR]

In exchange-coupled two-phase permanent magnets, the length scale of soft phase is limited to about twice of the domain-wall width of the hard phase. To optimize the energy product, it is important to realize this length experimentally. In this work, we investigate the Sm-Co/Co hard/ soft multilayers with varying thickness of soft phase layers. On rapidly annealing, the multilayered hard-soft structure forms. Transmission electron microscopy micrography confirms that the multilayer structure is retained after the annealing. Single-phase-like hysteresis loops are obtained for samples with Co layers up to 13 nm thick. This behavior indicates that the soft phase is well exchange coupled to the neighboring SmCoz hard phase. An optimal energy product of 16.6 MGOe has been obtained. Longer annealing time results in more diffusion at the interface and yields two-phase-like hysteresis behavior. Direct current demagnetization measurement shows exchange-spring behavior of the samples annealed for longer time. Micromagnetic simulations with varying interface exchange coupling have been performed to compare with the experimental results. [ABSTRACT FROM AUTHOR]

Nanochannels of porous alumina films were used as nanoreactors for the reaction of hydrogen gas with a mixture of Fe nitrate and Pt chloride. This results in the formation of of FePt clusters within the nanochannels. Both the sizes of the clusters and the coercivity the cluster assembly increase with the increase of annealing temperature. In order to reduce excessive agglomeration at high temperature, carbon was introduced by chemical vapor deposition and FePt:C composites in nanoscale channels were created. When FePt clusters were synthesized with carbon and heat treated at high temperatures, cluster sizes were much smaller than those without carbon, suggesting that the introduced carbon serves effectively to block the agglomeration of clusters. The coercivity of the FePt:C composite containing the smaller clusters is as high as 29.0 kOe. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

FePt and Fe3O4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometry. Loading the templates with an Fe chloride and Pt chloride mixture, followed by hydrogen reduction at 560 °C, leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. An Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe3O4 tubes. The versatility of the method indicates that materials with a wide range of parameters can be produced. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The relationship between the phase evolution, nanostructure, exchange coupling, and magnetic properties of Nd[sub 8.4]Fe[sub 86]Mo[sub l.1]B[sub 4.5] magnets prepared by melt spinning (MS) and mechanical milling (MM) are studied by x-ray diffraction, Mössbauer spectroscopy, positron lifetime measurements, high resolution transmission electron microscopy observations, and magnetization measurements. The maximum magnetic energy product (BH)[sub max] for MM magnets annealed at 650 °C or below are notably higher than those of the corresponding MS samples due to the larger amount of the Nd(Fe,Mo)[sub 7] present in the MS samples. [ABSTRACT FROM AUTHOR]

Presents a study that examined the structure and magnetic properties of neodymium-iron-titanium alloys and their nitrides. Methodology; Analysis of the magnetic coercivities of the samples; Examination of the dependence of the magnetic properties on the composition of the samples.