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Title: Internal dipolar field and soft magnons in periodic nanocomposite magnets

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Magnetism and Magnetic Materials
Additional Journal Information:
Journal Volume: 433; Journal Issue: C; Related Information: CHORUS Timestamp: 2017-10-04 15:56:56; Journal ID: ISSN 0304-8853
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Citation Formats

Belemuk, A. M., and Chui, S. T. Internal dipolar field and soft magnons in periodic nanocomposite magnets. Netherlands: N. p., 2017. Web. doi:10.1016/j.jmmm.2017.02.051.
Belemuk, A. M., & Chui, S. T. Internal dipolar field and soft magnons in periodic nanocomposite magnets. Netherlands. doi:10.1016/j.jmmm.2017.02.051.
Belemuk, A. M., and Chui, S. T. Sat . "Internal dipolar field and soft magnons in periodic nanocomposite magnets". Netherlands. doi:10.1016/j.jmmm.2017.02.051.
title = {Internal dipolar field and soft magnons in periodic nanocomposite magnets},
author = {Belemuk, A. M. and Chui, S. T.},
abstractNote = {},
doi = {10.1016/j.jmmm.2017.02.051},
journal = {Journal of Magnetism and Magnetic Materials},
number = C,
volume = 433,
place = {Netherlands},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.jmmm.2017.02.051

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  • Here, we present a simple analytical model to estimate the magnetization (σ s) and intrinsic coercivity (Hci) of a hard/soft nanocomposite magnet using the mass fraction. Previously proposed models are based on the volume fraction of the hard phase of the composite. But, it is difficult to measure the volume of the hard or soft phase material of a composite. We synthesized Sm 2Co 7/Fe-Co, MnAl/Fe-Co, MnBi/Fe-Co, and BaFe 12O 19/Fe-Co composites for characterization of their σs and Hci. The experimental results are in good agreement with the present model. Therefore, this analytical model can be extended to predict themore » maximum energy product (BH) max of hard/soft composite.« less
  • The time evolution of magnons subject to a time-dependent microwave field is usually described within the so-called 'S-theory', where kinetic equations for the distribution function are obtained within the time-dependent Hartree-Fock approximation. To explain the recent observation of 'Bose-Einstein condensation of magnons' in an external microwave field [Demokritov et al., Nature (London) 443, 430 (2006)], we extend the S-theory to include the Gross-Pitaevskii equation for the time-dependent expectation values of the magnon creation and annihilation operators. We explicitly solve the resulting coupled equations within a simple approximation where only a single condensed mode is retained. We also re-examine the usualmore » derivation of an effective boson model from a realistic spin model for yttrium-iron garnet films and argue that in the parallel pumping geometry (where both the static and the time-dependent magnetic field are parallel to the macroscopic magnetization) the time-dependent Zeemann energy cannot give rise to magnon condensation.« less
  • Metal amorphous nanocomposites (MANCs) are promising soft magnetic materials (SMMs) for power electronic applications offering low power loss at high frequency and maintaining a relatively high flux density. While applications in certain motor designs have been recently modeled, their widespread application awaits scaled manufacturing of MANC materials and proliferation of new higher speed motor designs. A hybrid motor design based on permanent magnets and doubly salient stator and rotor is reported here to develop a compact (a factor of 10 smaller than currently possible in Si steels), high-speed (>1 kHz, electrical), high-power (>2.5 kW) motor by incorporating low loss (<10more » W/kg at 1 kHz) MANCs such as recently reported Fe-Ni-based alloys. A feature of this motor design is flux focusing from the permanent magnet allowing use of lower energy permanent magnet chosen from among non-rare earth containing compositions and attractive due to constraints posed by rare earth criticality. A 2-D finite element analysis model reported here indicates that a 2.5 kW hybrid motor may be built with a permanent magnet with a 0.4 T remanence at a rotor speed of 6000 rpm. At a magnetic switching frequency of 1.4 kHz, the core loss may be limited to <3 W by selecting an appropriate MANC SMM. The projected efficiency exceeds 96% not including power loss in the controller. Under full load conditions, the flux density distributions for the SMM stay predominantly <1.3 T, the saturation magnetization of optimized FeNi-based MANC alloys. As a result, the maximum demagnetizing field in the permanent magnet is less than 2.2 × 10 5 A/m sustainable, for example, with a high-grade hard ferrite magnet.« less
  • The influence of multiple elastic scattering on the magnon parametric excitation in low-dimensional magnets is studied. The multiple-scattering results in the strong backscattering of magnons. This backscattering can interfere with the parametric excitation because both phenomena involve pairs of magnons with opposite momenta. It is shown that the influence of the backscattering on the threshold of parametric excitation in two-dimensional systems is proportional to the logarithm of the size, even if it exceeds the inelastic mean free path. The possibilities of experimental observation of the effect are discussed.
  • We present results for the magnetic-field, temperature, and neutron-polarization dependence of the small-angle neutron scattering intensity in the soft magnetic iron-based nanocomposite Nanoperm (Fe{sub 89}Zr{sub 7}B{sub 3}Cu). An unusual 'clover-leaf-shaped' intensity distribution on the detector is attributed to the dipolar stray fields around the nanosized iron particles, which are embedded in an amorphous magnetic matrix of lesser saturation magnetization. The dipole field induces spin disorder, correlating the spin misalignment of neighboring particles and matrix over several particle spacings. The clover-leaf-shaped anisotropy is observed over a wide range of applied magnetic field and momentum transfer. It persists up to several hundredmore » degrees Kelvin above the Curie temperature of the matrix phase, indicating that some degree of magnetic coupling persists even when the matrix is paramagnetic.« less