Volume 107, Issue 9, 01 May 2010
Index of content:
- PROCEEDINGS OF THE 11TH JOINT MMM-INTERMAG CONFERENCE, WASHINGTON, DC, 2010
- Soft Magnetic Materials and Domains
107(2010); http://dx.doi.org/10.1063/1.3334168View Description Hide Description
Results on the magnetic behavior of glass-coated amorphous wires with metallic nucleus diameters in the submicron range are reported for the first time. The magnetic behavior of nearly zero magnetostrictive submicron amorphous wires is different from that observed in amorphous microwires with typical dimensions and similar composition. Submicron wires are bistable, whereas typical microwires show an almost anhysteretic loop. Bistability of submicron wires is maintained even in a very thin surface layer, which was shown to display a helical magnetic anisotropy. The origin of this specific behavior is the shape anisotropy which becomes dominant at lower dimensions of the metallic nucleus. The study of submicron amorphous wires opens up the way for new applications of amorphous wires.
107(2010); http://dx.doi.org/10.1063/1.3334169View Description Hide Description
Amorphousironnanoparticles were synthesized using an aqueous reduction in iron(II) sulfate with sodium borohydride and sodium citrate. Various radio frequency (rf) exposure times were investigated in order to determine trends in nonclassical crystallization. RF times from 15 to 300 s revealed an increase in crystallite size from 5 to 60 nm, as determined by powderx-ray diffraction. Also, solvent optimization revealed that ethanol produced the largest trends for increasing crystallite size without total oxidation of the samples. Magnetic characterization by room temperature vibrating sample magnetometry and high resolution transmission microscopy was performed to verify magnetic properties and particle morphology.
107(2010); http://dx.doi.org/10.1063/1.3334170View Description Hide Description
Fe–Ni alloy nanoparticles were synthesized by polyol process using hydrazine as a reduction assist reagent. Particle size, crystallite size, and crystal phases varied with the type of polyol. The saturation magnetizations of the as-synthesized Fe–Ni particles synthesized in ethylene glycol (EG) and 1-heptanol were similar to the bulk and were 73 emu/g and 83 emu/g, respectively. On the other hand, the coercivities of the same were 41 and 123 Oe. The coercivity of the Fe–Ni particles synthesized in EG decreased to 27 Oe after heat treatment. Though the magnetic properties were very similar irrespective of the polyol used in this study, the Mössbauer spectroscopic measurements revealed that Fe–Ni particles with single permalloy phase was synthesized only when EG was used.
107(2010); http://dx.doi.org/10.1063/1.3334172View Description Hide Description
nanoparticles were synthesized by aqueous reduction in iron (II) sulfate and cobalt (II) sulfate using sodium borohydride and sodium citrate. The initial concentrations of iron and cobalt were varied while maintaining an overall metal concentration of 4.60 mM. Increasing the cobalt content from 0 to 100 at. % decreased the magnetization saturation from 152 to 48 emu/g, as determined by room temperature vibrating sample magnetometry. Annealing the samples at 450 and showed an increase in crystallite size. Powderx-ray diffraction and transmission electron microscopy was performed to determine the phases and morphology of the materials.
107(2010); http://dx.doi.org/10.1063/1.3334173View Description Hide Description
A systematic investigation of the influence of Al and V on the magnetoimpedance (MI) effect in melt-spun (, 1, 1.5, and 3) ribbons has been performed in the frequency range 500 kHz–13 MHz and under dc magnetic field up to 60 Oe. MI was measured using impedance analyzer employing contact and noncontact methods. MIs of 61% (contact method) and (noncontact method) were observed for the ribbon. Transverse and in-plane anisotropies were studied from the MI measurements and ferromagnetic resonance. Magnetic domain structure was studied in the ribbons through magnetic force microscopy. When the ribbon was rotated by 90° from the east-west direction, a 37% change in the MI was observed due to the earth’s magnetic field.
107(2010); http://dx.doi.org/10.1063/1.3334197View Description Hide Description
nanoparticles were synthesized in an induction plasma torch and oxidized isochronally at temperatures between room temperature (RT) and . The particles exhibited three stages of oxidation present at different temperatures. The initial oxide layer was nearly Co-free, beginning at 3 nm at RT, and Co appeared to oxidize separately from the iron.Iron cations were determined to be the mobile species during oxidation, yielding a progressively more Co-rich core as oxidation progressed, decreasing from an average diameter of 42 to 25 nm, while the oxide tripled in size. At , the particles exhibited a less dense core, and at the particles were observed to have changed morphology completely with some sintering, forming completely oxidized particles with an average diameter three times the as received size.
107(2010); http://dx.doi.org/10.1063/1.3334198View Description Hide Description
We report on new metastable -FeNi nanoparticles produced by mechanical alloying of melt-spun ribbon using a high energy ball mill followed by a solution annealing treatment in the -phase region and water quenching in of the face-centered cubic -phase. In the Fe–Ni phase diagram there is a strong compositional dependence of the Curie temperature,, on composition in the -phase. This work studies the stabilization of -phase nanostructures and the compositional tuning of in Fe–Ni alloys which can have important ramifications on the self-regulated heating of magnetic nanoparticles in temperature ranges of interest for applications in polymer curing and cancer thermotherapies. To date we have achieved Curie temperatures as low as by this method.
Preparation and structural characterization of FeCo epitaxial thin films on insulating single-crystal substrates107(2010); http://dx.doi.org/10.1063/1.3334200View Description Hide Description
FeCo epitaxialfilms were prepared on MgO(111), , and single-crystal substrates by ultrahigh vacuum molecular beam epitaxy. The effects of insulating substrate material on the film growth process and the structures were investigated. filmsgrow on MgO substrates with two type domains, Nishiyama–Wassermann (NW) and Kurdjumov–Sachs (KS) relationships. On the contrary, FeCo filmsgrown on and substrates include crystal in addition to the crystals with NW and KS relationships. The crystal consists of two type domains whose orientations are rotated around the film normal by 180° each other. The out-of-plane and the in-plane lattice spacings of and crystals formed on the insulating substrates are in agreement with those of the bulk (at. %) crystal with small errors ranging between and , showing that the strains in the epitaxialfilms are very small.
107(2010); http://dx.doi.org/10.1063/1.3334201View Description Hide Description
Precipitates in the form of grain growth inhibitors play an essential role in the production of grain-oriented electrical steels, as they promote the development of Goss texture during secondary recrystallization. However, the presence of precipitates in the final material can have a detrimental effect on loss and permeability, as they impede domain wall motion during the magnetization process. In previous work [K. Jenkins and M. Lindenmo, J. Magn. Magn. Mater.320, 2423 (2008)], a conventional grain-oriented electrical steel was presented that contained very fine precipitates, which did not damage the bulk magnetic properties. In this article the influence of precipitate size is investigated by comparing local Barkhausen noise measurements and electron backscatter diffraction analysis for a number of grain-oriented electrical steels, which are metallurgically similar except for the size and abundance of precipitates.
- Hard Magnetic Materials
107(2010); http://dx.doi.org/10.1063/1.3334458View Description Hide Description
The structure and magnetic properties were studied for bulk nanocrystallinesinteredmagnet produced by spark plasma sintering technique. X-ray diffraction patterns show that the sinteredmagnet exhibits crystal structures.Transmission electron microscopy(TEM) observation indicates the average grain size of the magnet of about 40 nm. Magnetic measurement shows that the coercivity reaches as high as 2.85 T; the saturation magnetization and the remanence are 0.71 and 0.5 T, respectively. The magnet exhibits good thermal stability with a coercivity of 0.9 T at 773 K and a coercivity coefficient of −0.15%/K.
Phase structure, magnetic properties, and magnetization behavior of nanocomposite made by mechanical alloying107(2010); http://dx.doi.org/10.1063/1.3334459View Description Hide Description
The nanocompositepermanent magnets are produced by mechanical alloying and subsequent annealing. The soft magnetic phases were introduced by two different processes. In the first process, the crushed as-cast powders were blended and milled with different weight percent of fine iron powders and in the second process, the crushed as-cast powders (SCZF) were milled directly. XRD analysis showed that the phase structure of annealed are consisted of phase and phase, while the composites of annealed SCZF are composed of and SmCo hard phases that varied with different Fe content. The best energy product of the annealed SCZF and are 11.3 MGOe (SCZF-3) and 10 MGOe , respectively, resulting from the very strong exchange coupling between the hard phase and the soft phase. According to the Henkel-plots of SCZF-3 and , a stronger intergrain exchange coupling effect was observed in SCZF-3 sample. The irreversible nucleation fields of SCZF-3 and are also studied in detail.
Effects of particle size and composition on coercivity of Sm–Co nanoparticles prepared by surfactant-assisted ball milling107(2010); http://dx.doi.org/10.1063/1.3334460View Description Hide Description
The (, 4, 5, 6, 8.5, and 10) magnetic nanoparticles with different composition have been prepared by surfactant-assisted ball milling technique. By controlling the settle-down time and the centrifugation conditions, the nanoparticles with different particle size and narrow size distribution were successfully obtained. It was observed that the SmCo nanoparticles become unstable with increasing Sm content. It was also observed that the coercivity of the nanoparticles increases with Co content and particle size, indicating a complex effect of the particle size and composition on magnetic hardening of the hard magnetic nanoparticles.
107(2010); http://dx.doi.org/10.1063/1.3334493View Description Hide Description
Composite magnets containing Sm–Co and Co phases were prepared from high-energy-milled Sm–Co and Sm–(Co,Fe,Mn) powders with the 1:5 and 2:7 stoichiometries blended with a micron-size Co powder. The blending was done via high-energy milling in argon or heptane; the blends were subsequently consolidated at and subjected to a 65% plastic deformation at . Both the premilling of Sm–Co component and the processing environment markedly influenced the microstructure and magnetic properties of the resulting composites. After blending in heptane, the composites made from the 1:5 and Co phases still contained these two phases in addition to the emerging 2:17 phase. Addition of oleic acid as a surfactant led not only to a more uniform and refined microstructure but also to a significant oxidation. After blending in argon, the composites made from the 1:5(2:7) and Co phases exhibited a two-phase structure with 80 nm Co inclusions embedded in a 2:17 matrix. Unfortunately, the newly formed 2:17 phase did not inherit the texture induced in the 1:5(2:7) precursors by the hot-deformation. Although the argon-blended composites were magnetically superior to the heptane-blended ones, they exceeded the maximum energy product of the single-alloy magnets with the same overall composition only when the powder had been used as a precursor. The highest properties obtained were 8.8 kG, 6.3 kOe, and 13.1 MGOe for the remanence, coercivity, and energy product, respectively.
107(2010); http://dx.doi.org/10.1063/1.3334494View Description Hide Description
The effect of Ta addition on the structure and magnetic properties of melt-spun ribbons has been investigated. The intrinsic coercivity increases dramatically from 1.9 kOe for Ta-free ribbon to 9.8 kOe for ribbon, while further increasing Ta results in little enhancement of the coercivity.XRD patterns reveal that ribbons crystallize in the pure -type structure for low Ta substitution of and a minor phase of appears when . According to Rietveldstructure refinement, the ternary alloying element Ta prefers to occupy the site of -type structure. The mechanism of the coercivity enhancement has been discussed based on crystal structure and microstructure.
Effects of substrate temperature and Cu underlayer thickness on the formation of epitaxial thin films107(2010); http://dx.doi.org/10.1063/1.3334539View Description Hide Description
epitaxialthin films were prepared on Cu(111) underlayers heteroepitaxially grown on single-crystal substrates by molecular beam epitaxy. The effects of substrate temperature and Cu underlayer thickness on the crystallographic properties of epitaxialfilms were investigated. The Cu atoms of underlayer diffuse into the film and substitute the Co sites in structure forming an alloy compound of . The ordered phase formation is enhanced with increasing the substrate temperature and with increasing the Cu underlayer thickness. The Cu atom diffusion into the film is assisting the formation of ordered phase.
The magnetization behavior and magnetic viscosity of ribbons with different temperature dependence of coercivity107(2010); http://dx.doi.org/10.1063/1.3334540View Description Hide Description
Two types of ribbons with different temperature dependence of coercivity are investigated in comparison at different temperatures. It is found that their magnetization behaviors and magnetic viscosity are distinctly different. The magnetization of sample A (with abnormal temperature dependence of coercivity) behaves as a single phase permanent magnet at room temperature, and then becomes similar to a nanocompositemagnet with the increase of temperature. However, sample B (with negative temperature coefficient of coercivity) is similar to a nanocompositemagnet at the whole temperature range. The magnetic viscosity is mainly determined by the irreversible magnetization for both ribbons, while there emerges an extra small peak of magnetic viscosity coefficient at low field and high temperature for sample B. The different content and distribution of Cu in the cell boundary phase are proposed to be responsible for the differences of temperature dependence of coercivity,magnetization, and magnetic viscosity behaviors of these two types of ribbons.
107(2010); http://dx.doi.org/10.1063/1.3334541View Description Hide Description
and epitaxialthin films with the -axis perpendicular to the substrate surface are successfully prepared on Cu underlayers heteroepitaxially grown on MgO(111) single-crystal substrates. The nucleation behavior of and crystals on Cu(111) underlayers were investigated. The and the films consist of two types of domains whose orientations are rotated around the film normal by 30° each other, whereas the film is a single crystal. The nucleation and the domain volume ratio seem to be controllable by adjusting the kind and the composition of transition metal elements.
107(2010); http://dx.doi.org/10.1063/1.3334542View Description Hide Description
Structure and magnetic properties were studied for bulk nanocrystallinemagnet synthesized by spark plasma sintering technique. X-ray diffraction results indicate both ingot and sinteredmagnet of alloy exhibit hexagonal type structure. The microstructure of the magnet is composed of type nanograins with an average size of 35 nm detected by transmission electron microscopy and selected area electron diffraction patterns. Magnetic measurement shows that the remanence of the magnet is higher at 573 K than at 300 K, indicating there is a positive remanence temperature coefficient in the magnet. The anisotropy field of alloy is 3.8 T, which is much higher than the of 2.3 T for the pure alloy. The coercivity of the sinteredmagnet increases from 0.25 to 0.354 T after optimal annealing.
107(2010); http://dx.doi.org/10.1063/1.3334543View Description Hide Description
The crystal structure and magnetic properties of melt spun (, Cr, and Mo;) ribbons have been investigated. Based on x-ray diffraction analysis, it is found that a pure -type structure is formed in the melt spun ribbons, while minor amount of additional 2:17 phase appears for the ( and Mo;) ribbons, implying that the elements in group (Cr and Mo) are inferior to the element in group (Ta) in stabilizing metastable 1:7 phase. The result, analyzed by Rietveld refinement method, shows that Ta, Cr, and Mo may occupy the 2e site of 1:7 phase, which leads to the enhancement of the magnetic anisotropy field of 1:7 phase, just like Ti, Zr, Hf, Nb, or V did. From the magnetic performance point of view, with increasing the content of doping element x from 0 to 0.6, the maximum coercivity of ribbons is enhanced from 1.9 kOe for binary to 11.3 kOe for , 6.6 kOe for , and 7.5 kOe for , respectively, while the remanent magnetization is all reduced for the above ternary alloy ribbons.
- Magneto-Optic, Magnetoelastic, and Magnetocaloric Materials
107(2010); http://dx.doi.org/10.1063/1.3335498View Description Hide Description
The thermal stability, magnetocaloric effect, and refrigeration capacity (RC) of Gd-based glassy ribbons have been investigated. A relatively wide supercooled liquid region (50–80 K) and large reduced glass transition temperature are found in glassy ribbons. The distinctive glass transition and sharp crystalline events as well as large values of and confirm the excellent glass forming ability of these alloys. The maximal magnetic entropy changes, , and RC values of the specimens are about 4.80–5.21 J/kg K and 700–800 J/kg under 50 kOe, respectively. These values are comparable to or even higher than that of some reported bulk metallic glasses. Moreover, the larger RC values are due to the broad peak , which is caused by the glassy structure. The large and RC values make the Gd-based glassy ribbons attractive candidates for magnetic refrigeration materials.