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1 Apr 2012

Volume 111, Issue 7 (partial)

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back to top Soft Magnetic Materials

Effect of P addition on nanocrystallization and high temperature magnetic properties of low B and Nb containing FeCo nanocomposites

Rajat K. Roy, S. Shen, S. J. Kernion, and M. E. McHenry

J. Appl. Phys. 111, 07A301 (2012); doi:10.1063/1.3670056 (3 pages)

Online Publication Date: 6 February 2012

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The P content dependencies of the nanocrystallization behaviors and high temperature magnetic properties of the Fe54.6Co29.4Si2.8(B0.8−YPY)14Nb1Cu1 (Y = 0, 0.2, and 0.3) alloys have been investigated. Alloys were prepared by melt spinning and subsequently annealed in an argon atmosphere to induce nanocrystallization. P addition increases primary crystallization temperature (Tx1), thermal stability (ΔTx), and activation energy (QJMA) for secondary crystallization in as-cast alloys. The saturation induction (Bs) of 1.68 T for as-cast P free alloy decreases continuously with the addition of P. However, the soft magnetic properties are enhanced for P added alloys. The XRD pattern reveals that grain refinement increases with increasing P contents. Alloys annealed at 430 °C confirm primary nanocrystallization of α-FeCo in the amorphous matrix, while annealing at 550 °C causes secondary crystallization of other non-magnetic phases as well. The magnetic moment of as-cast and annealed alloys, measured by vibrating sample magnetometry (VSM), has minimum values at two temperatures, labeled Tc1, Tc2, prior to secondary crystallization, corresponding to the ferromagnetic transitions of as-quenched amorphous and residual amorphous phase, respectively. The stabilization of amorphous phase delays primary crystallization, resulting in increase of Tc1 for P-rich as-cast alloys.
Show PACS
75.75.Cd Fabrication of magnetic nanostructures
81.40.Gh Other heat and thermomechanical treatments
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Domain structure and magnetization loss in a toroidal core based on an Fe-based amorphous alloy

Daichi Azuma, Ryusuke Hasegawa, Shin Saito, and Migaku Takahashi

J. Appl. Phys. 111, 07A302 (2012); doi:10.1063/1.3670065 (3 pages)

Online Publication Date: 7 February 2012

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By utilizing a wide-view Kerr-effect magnetic domain observation system designed for domain observation on curved surfaces, domain images were taken on the surface of a toroidal core based on an Fe-based amorphous alloy. The results of the observation are discussed in terms of Bertotti’s eddy-current loss model, helping to clarify the concept of magnetic objects proposed by the model.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
78.20.Ls Magneto-optical effects

Structural studies of high-Ku metastable CoPt thin films with long-range order

Fu-Te Yuan, Jen-Hwa Hsu, Yi-Hung Lin, S. N. Hsiao, and H. Y. Lee

J. Appl. Phys. 111, 07A303 (2012); doi:10.1063/1.3670511 (3 pages)

Online Publication Date: 8 February 2012

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The symmetries of CoPt thin films in different phases, including disordered A1, ordered L11, and L10 were examined by making measurements along the (10.1) diffraction rod. The films were deposited by sputtering on MgO(111) substrates at different temperatures (Ta). The stacking sequence of close-packed atomic planes in 50 nm-thick samples with Ta ≥ 200 °C was identified as ABCABC, indicating that the distribution of defects in the film was random, so the symmetry was preserved with increasing Ta. In the RT-prepared film, a considerable amount of (∼62.9 vol.%) disordered CoPt with hexagonal symmetry was detected, vanishing as Ta increased. Defect-induced modification of symmetry was observed in the L11 film as its thickness was reduced to 10 nm. A pseudo-hcp component of around 7.1 vol.% was present in the film, as a result of the periodic distribution of defects. The defects in the structure may also explain the broadened magnetic alignment.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
77.55.F- High-permittivity capacitive films

Tuning of magnetization dynamics in sputtered CoFeB thin film by gas pressure

Feng Xu, Qijun Huang, Zhiqin Liao, Shandong Li, and C. K. Ong

J. Appl. Phys. 111, 07A304 (2012); doi:10.1063/1.3670605 (3 pages)

Online Publication Date: 9 February 2012

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The influences of sputtering gas pressure on the high-frequency magnetization dynamics of as-sputtered CoFeB thin films are studied with permeability spectra based on the Landau-Lifshitz-Gilbert (LLG) equation. Results show that with the pressure increasing, both the anisotropy field and resonance frequency have minimums, while the initial permeability shows a maximum. The damping factor deceases monotonously with the pressure increasing, similar as with the coercivity. The high tunability of the damping factor indicates that controlling sputtering gas pressure could be an effective method in tuning the magnetization dynamics. All these dependences on gas pressure are suggested to be related to the inner stress of these sputtered films.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
68.60.Bs Mechanical and acoustical properties

Magnetic behaviour of Ni0.4Zn0.6Co0.1Fe1.9O4 spinel nano-ferrite

Atul Thakur, Preeti Thakur, and Jen-Hwa Hsu

J. Appl. Phys. 111, 07A305 (2012); doi:10.1063/1.3670606 (3 pages)

Online Publication Date: 9 February 2012

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Nanoparticles of the spinel ferrite Ni0.4Zn0.6Co0.1Fe1.9O4, have been synthesized by a co-precipitation method. The x-ray diffraction patterns of the particles confirmed the formation of single-phase cubic spinel structure. The Langevin function fitting on M-H data at 300 K gives a log-normal particle size distribution with median diameter of 59.6 nm and standard deviation of 0.6. The isothermal dc magnetization studies have been performed using the superconducting quantum interface device and vibrating sample magnetometer in the temperature range of 5-300 K. These measurements show that the sample is superparamagnetic above the blocking temperature TB ∼ 253 K when an external magnetic field of 20 Oe is applied. The reduction in saturation magnetization in case of nanoparticles may be attributed to the fact that magnetic moments in the surface layers outside the core are in the state of frozen disorder. A doublet observed in the Mössbauer study also confirms the superparamagnetic behavior and nanocrystalline formation.
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81.16.-c Methods of micro- and nanofabrication and processing
75.30.Cr Saturation moments and magnetic susceptibilities
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Volume exchange in soft FeCo films of high magnetization

Christoph Mathieu, Hau-Jian Liu, Kristen S. Buchanan, and Venkateswara R. Inturi

J. Appl. Phys. 111, 07A306 (2012); doi:10.1063/1.3670975 (3 pages)

Online Publication Date: 10 February 2012

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Soft FeCo films of high magnetization are a well known integral part of today’s magnetic recording heads. Values for the volume exchange, an important parameter since it determines exchange length, domain wall width, and energy are, however, available for few compositions of FeCo in spite of the widespread use of these alloys. This paper presents results for volume exchange on Fe65Co35 determined by means of a detailed Brillouin light scattering study, one of a few methods that permit the measurement of exchange. A set of Fe65Co35 films of various thickness values was examined, and volume exchange was found to be 3.5 × 10–6 erg/cm, far higher than what is often assumed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Bulk nanocomposite using self-forming core/shell nanoparticles and its magnetic properties for high-frequency applications

Tomohiro Suetsuna, Koichi Harada, Toshihide Takahashi, and Seiichi Suenaga

J. Appl. Phys. 111, 07A307 (2012); doi:10.1063/1.3670977 (3 pages)

Online Publication Date: 10 February 2012

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A bulk nanocomposite composed of tightly packed self-forming core/shell nanoparticles of metal/oxide was fabricated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition were controlled in the nanocomposite, and their effects on the magnetic properties were investigated. The crystalline grain size of the nanoparticles, the packing ratio, and the composition strongly influenced the magnetic anisotropy field, magnetic coercivity, relative permeability, and loss factor at GHz bands. High permeability with a low loss factor of less than 1.5% at up to 1 GHz was obtained in the nanocomposite in which the nanoparticles with a crystalline grain size of approximately 15 nm were tightly packed.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
back to top Ferrites, Garnets, and Microwave Materials

Skin effect suppression for Cu/CoZrNb multilayered inductor

Noriyuki Sato, Yasushi Endo, and Masahiro Yamaguchi

J. Appl. Phys. 111, 07A501 (2012); doi:10.1063/1.3670061 (3 pages)

Online Publication Date: 6 February 2012

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The Cu/Co85Zr3Nb12 multilayer is studied as a conductor of a spiral inductor to suppress the skin effect at the 5 GHz range (matches IEEE 802.11 a standard) using negative-permeability in CoZrNb films beyond the ferromagnetic resonance frequency. The skin effect suppression becomes remarkable when the thickness of Cu in each period of the multilayer, tCu, is less than the skin depth of Cu at the targeting frequency. For the 5 GHz operation, tCu ≤ 750 nm. The resistance of the Cu/CoZrNb multilayered spiral inductor decreases as much as 8.7%, while keeping the same inductance of 1.1 nH as that of a similar air core. Accordingly, Q = 16. Therefore, the proposed method can contribute to realize a high-Q spiral inductor. We also study the potentially applicable frequency of this method. Given a soft magnetic material with Ms = 105 emu/cc and Hk = 5 Oe, the method can be applied at 700 MHz, the lowermost carrier frequency band for the 4th generation cellular phone system.
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84.32.Hh Inductors and coils; wiring
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
back to top Hard Magnetic Materials

The partitioning of Dy and Tb in NdFeB magnets: A first-principles study

X. B. Liu and Z. Altounian

J. Appl. Phys. 111, 07A701 (2012); doi:10.1063/1.3670054 (3 pages)

Online Publication Date: 6 February 2012

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Doping with Dy/Tb is a current solution to improve the coercivity and the operating temperature of NdFeB magnets, by increasing the magnetocrystalline anisotropy of the (Nd, Dy/Tb)2Fe14B (2:14:1) phase. The efficiency of Dy/Tb doping depends on the distribution of Dy/Tb in the multi-phase microstructure of the NdFeB magnet. To understand and control the Dy/Tb redistribution, the partitioning of Dy/Tb between 2:14:1 and Nd-rich phases has been studied by a first-principles density functional calculation. The total energy calculations indicate that Dy and Tb prefer to enter the 4f sites in the 2:14:1 phase. The substitution energies of Dy and Tb in 2:14:1 are negative and are −0.35 eV/atom and −0.33 eV/atom, respectively, as Nd is replaced with 25% of Dy/Tb, i.e., stabilizing the 2:14:1 structure. However, the substitution energies of Dy and Tb in NdO have large positive values. They are 0.83 eV/atom and 0.73 eV/atom for Dy and Tb, respectively, when 25% of Nd is replaced by Dy/Tb. The results indicate that Dy/Tb prefer to enter the 2:14:1 phase rather than the Nd-rich phase (NdO). This is the thermodynamic origin for the selective occupation of Dy and Tb in the 2:14:1 structure which enhances the magnetic anisotropy field.
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75.30.Gw Magnetic anisotropy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
61.72.U- Doping and impurity implantation
75.50.Vv High coercivity materials

Effect of intrinsic tensile stress on (001) orientation in L10 FePt thin films on glass substrates

S. N. Hsiao, S. H. Liu, S. K. Chen, F. T. Yuan, and H. Y. Lee

J. Appl. Phys. 111, 07A702 (2012); doi:10.1063/1.3670515 (3 pages)

Online Publication Date: 8 February 2012

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Single-layered FePt thin films were deposited on glass substrates and subsequently annealed at 800 °C for various times in a rapid thermal annealing (RTA) furnace. Near-fully-L10-ordered FePt films were obtained after RTA. The accumulation of the intrinsic tensile stress is mainly contributed by the densification reaction, which leads to the development of (001) preferred orientation. The relief of the tensile stress predominantly stems from the microstructural variation (from continuous to interconnected network state), resulting in a reduction of (001) texture. Enhanced perpendicular magnetic and crystalline anisotropy was obtained for the films annealed for 900 s, confirmed by a high Lotgering orientation factor of 0.99 and differential squareness of 0.5. The results provide direct evidence that intrinsic tensile stress prompts the (001) preferred orientation through suggested strain-induced grain growth.
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68.55.jm Texture
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.60.Bs Mechanical and acoustical properties
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Investigation of easy axis orientation of Nd–Fe–B melt-spun ribbons produced by hot rolling and influence of Ti–C addition

M. Takezawa, Y. Nakanishi, Y. Morimoto, J. Yamasaki, and M. Yagi

J. Appl. Phys. 111, 07A703 (2012); doi:10.1063/1.3670976 (3 pages)

Online Publication Date: 10 February 2012

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The c-axis orientation of Nd–Fe–B melt-spun ribbons caused by hot rolling and the influence of Ti–C addition were investigated. A small roll was placed on a steel wheel near a quartz tube in such a manner that the melt-spun ribbons were hot rolled immediately after quenching. X-ray diffraction patterns measured on both surfaces of the Nd–Fe–B–Ti ribbon indicate that the c-axis is oriented normal to the ribbon plane. The domain pattern of the Nd–Fe–B–Ti–C ribbon was observed with a Kerr microscope. Most of the grains exhibit a maze domain configuration, indicating that the c-axis is oriented normal to the ribbon plane. Furthermore, it was demonstrated that hot rolling and the addition of Ti–C promote c-axis orientation and high coercivity of Nd–Fe–B melt-spun ribbons.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
78.20.Ls Magneto-optical effects
75.60.Ch Domain walls and domain structure
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effects of substrate on structure and the magnetic properties of (001)-textured FePt films grown at low temperature

A. M. Zhang, Z. X. Chen, W. Q. Zou, B. Lv, J. J. Ge, H. L. Cai, J. Du, X. S. Wu, S. J. Zhang, and S. M. Zhou

J. Appl. Phys. 111, 07A704 (2012); doi:10.1063/1.3670986 (3 pages)

Online Publication Date: 10 February 2012

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(001)-oriented FePt films are deposited, by magnetron sputtering at 300 °C, on LaAlO3 (001), SrTiO3 (001), and MgO (001) single crystal substrates. The tetragonal distortion, magnetic anisotropy, and the coercive force of the films vary with the substrate. The ordering process is very different with the substrate, which may affect the magnetic properties of the film. The magnetic coercivity decreases with increasing the ordering parameter and the tetragonal distortion, which may be ascribed to the lattice strain.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Magnetic properties and microstructure of Nd-Fe-B sintered magnets with DyHx addition

Y. H. Liu, S. Guo, X. M. Liu, D. Lee, and A. R. Yan

J. Appl. Phys. 111, 07A705 (2012); doi:10.1063/1.3671426 (3 pages)

Online Publication Date: 13 February 2012

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The effects of DyHx addition on magnetic properties and microstructure of Nd-Fe-B sintered magnets were investigated. In order to obtain the best magnetic properties, the effects of sintering temperature and annealing time on magnetic properties were also investigated. The results shown that the addition of DyHx can affect the microstructure, increase the intrinsic coercivity (Hcj), and improve the thermal stability of sintered Nd-Fe-B magnets. The remanence (Br) and Hcj showed different variation trends as sintering temperature changes. Within a reasonable range, sintering at higher temperature can get higher Br but lower Hcj. The Hcj was further increased by heat treatment and annealing time was extended.
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75.60.Nt Magnetic annealing and temperature-hysteresis effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.-y Defects and impurities in crystals; microstructure
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
back to top Magneto-Optic, Magnetoelastic, and Magnetocaloric Materials

Effect of Mn substitution for Fe on magnetic and magnetostrictive properties of SmFe2 compound

Y. Wang, W. J. Ren, Z. H. Wang, Y. Q. Zhang, J. Li, and Z. D. Zhang

J. Appl. Phys. 111, 07A901 (2012); doi:10.1063/1.3669914 (3 pages)

Online Publication Date: 3 February 2012

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The structural, magnetic, and magnetostrictive properties of Sm(Fe1−xMnx)2 (0 ≤ x ≤ 0.20) alloys have been investigated. The alloys are almost single phase cubic Laves Sm(Fe, Mn)2 when x ≤ 0.15. The lattice parameter increases and Curie temperature and the magnetization at 295 K decrease with increasing Mn content of the Sm(Fe1−xMnx)2 compounds. The spin-reorientation temperature for ⟨110⟩ to ⟨111⟩ of Sm(Fe1−xMnx)2 decreases from 200 K for x = 0 to 140 K for x = 0.15, indicating the increasing anisotropy of the Mn-substituted compounds. The magnetostriction coefficient λ111 of the Sm(Fe1−xMnx)2 compounds slightly decreases with Mn substitution and maintains a value larger than 1900 ppm for 0 ≤ x ≤ 0.15. The linear anisotropic magnetostriction λa = λ‖ − λ⊥ for the Sm(Fe1−xMnx)2 alloys decreases with increasing Mn content, which may be ascribed to the decrease of λ111 and the increased anisotropy.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Dk Alloys
75.30.Gw Magnetic anisotropy

Effects of Ni addition on the magnetostriction and microstructures of Fe70−xPd30Nix high-temperature ferromagnetic shape memory alloys

Yin-Chih Lin and Chien-Feng Lin

J. Appl. Phys. 111, 07A902 (2012); doi:10.1063/1.3669915 (3 pages)

Online Publication Date: 3 February 2012

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This study investigated the effects of adding a third alloying element, Ni, to create Fe70−xPd30Nix (x = 2, 4, 6, and 8 at. % Ni) ferromagnetic shape memory alloys. The Ni replaced a portion of the Fe. The magnetostriction and microstructures of Fe70−xPd30Nix high-temperature ferromagnetic shape memory alloys were studied in detail. Investigation of the magnetostriction and microstructures indicated that the greater Ni amount in the Fe70−xPd30Nix alloys caused the less saturation magnetostriction at room temperature (RT); it was also observed that it was more difficult to generate an annealed recrystallization. However, greater Ni addition into the Fe70-xPd30Nix (x = 6 and 8 at. % Ni) alloys, the L10 + L1m twin phase decomposition into stoichiometric L10 + L1m + αbct structures could be suppressed when the alloys were aged at 500 °C for 100 h. The result was that the Fe70−xPd30Nix (x = 6 and 8 at. % Ni) alloys maintained a high magnetostriction and magnetostrictive susceptibility (Δλ‖s/ΔH) after the 500 °C/100 h aged treatment. This magnetic property of the Fe70−xPd30Nix (x = 6 and 8 at. % Ni) alloys is suitable for application in a high temperature (T > 500 °C) and high frequency environment.
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75.80.+q Magnetomechanical effects, magnetostriction
75.30.Cr Saturation moments and magnetic susceptibilities
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
61.66.Bi Elemental solids
61.66.Dk Alloys
62.20.fg Shape-memory effect; yield stress; superelasticity

Giant magnetostriction in tetragonally distorted antiperovskite manganese nitrides

T. Shimizu, T. Shibayama, K. Asano, and K. Takenaka

J. Appl. Phys. 111, 07A903 (2012); doi:10.1063/1.3670047 (3 pages)

Online Publication Date: 6 February 2012

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The discovery of giant magnetostriction exceeding 2000 ppm in Mn3CuN has stimulated the research of manganese antiperovskites from the perspective of forced magnetostriction. We discovered that Mn3SbN exhibits a large magnetostriction of up to 450 ppm in the tetragonally distorted ferromagnetic phase below the Curie temperature TC = 360 K. The magnitude of magnetostriction is enhanced by up to 1000 ppm without reduction of TC by partial replacement of the constituent elements. The present results are examined in terms of ferromagnetic shape memory effects.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Phase instability of magnetic ground state in antiperovskite Mn3ZnN: Giant magnetovolume effects related to magnetic structure

T. Hamada and K. Takenaka

J. Appl. Phys. 111, 07A904 (2012); doi:10.1063/1.3670052 (3 pages)

Online Publication Date: 6 February 2012

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We verified the intimate relation between magnetism and volume in Mn3ZnN. The sample sintered at 900 °C is characterized by the Γ5g triangular antiferromagnetic (AF) state with larger volume below 170 K. However, for the sample sintered at 700 °C, the re-entrant phase transition appears at 80 K and the ground state is a different AF state with smaller volume. These results indicate that the ground state of Mn3ZnN is sensitive to the disorder in the N site and that the magnetic structure drastically alters magnetovolume effects. More detailed consideration is necessary beyond the conventional scheme, which incorporates only the amplitude of the magnetic moment.
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75.80.+q Magnetomechanical effects, magnetostriction
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Direct calorimetric measurements of isothermal entropy change on single crystal W-type hexaferrites at the spin reorientation transition

M. LoBue, V. Loyau, F. Mazaleyrat, A. Pasko, V. Basso, M. Kuepferling, and C. P. Sasso

J. Appl. Phys. 111, 07A905 (2012); doi:10.1063/1.3670062 (3 pages)

Online Publication Date: 6 February 2012

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We report on the magnetic field induced isothermal entropy change, Δs(Ha, T), of W-type ferrite with CoZn substitution. Entropy measurements are performed by direct calorimetry. Single crystals of the composition BaCo0.62Zn1.38Fe16O27, prepared by the flux method, are measured at different fixed temperatures under an applied field perpendicular and parallel to the c axis. At 296 K one deduces a value of K1 = 8.7 × 104  J m−3 for the first anisotropy constant, which is in good agreement with the literature. The spin reorientation transition temperature is estimated to take place between 200 and 220 K.
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75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
81.10.Dn Growth from solutions

The compressive stress effect on the magnetostriction and magnetization for Sm-Dy-Fe composites

Bowen Wang, Zhihua Wang, Yanming Hao, Ling Weng, Wenmei Huang, and Weili Yan

J. Appl. Phys. 111, 07A906 (2012); doi:10.1063/1.3670066 (3 pages)

Online Publication Date: 7 February 2012

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Sm0.88Dy0.12Fe2 rod composites were fabricated under a compaction pressure of 800 MPa along the rod direction and in a magnetic field of 200 kA/m along the direction, perpendicular to the rod axis. It is found that the magnetostriction λ|| parallel to the rod direction is almost unchanged with increasing the compressive stress up to 20 MPa and shows a large unsaturated magnetostriction value of −620 × 10−6 at 600 kA/m. The magnetostriction λ⊥ perpendicular to rod axis increases with increasing the compressive stress when the magnetic field is larger than 300 kA/m. The variation of the magnetostriction and magnetization with compressive stress has been discussed. This result is very important to application of Sm-Dy-Fe composites.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys

Behavior of magnetic field–annealed Galfenol steel

Michael Brooks, Eric Summers, J. B. Restorff, and M. Wun-Fogle

J. Appl. Phys. 111, 07A907 (2012); doi:10.1063/1.3670067 (3 pages)

Online Publication Date: 7 February 2012

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An attractive feature of the Galfenol alloy system is the ability to impart enough uniaxial anisotropy into the alloy such that no pre-load mechanism is required to attain saturation magnetostriction. Stress annealing is typically employed to generate this anisotropy. Recent published results indicate that magnetic field annealing could generate sufficient anisotropy to provide full magnetostriction with no prestress, which will suffice for the majority of applications. The magnetic field annealing apparatus used in these experiments applies a constant 1 T magnetic field at a temperature between 300 °C and 700 °C in a 7.6 cm square × 15.2-cm-long cavity. The magnetic behavior of field-annealed Galfenol is compared to stress-annealed samples. Field-annealed Galfenol rods behave differently than stress-annealed rods. While the saturation strain values are equivalent, the magnetic field required to saturate the Galfenol is much less, 60 Oe versus 200 Oe, in the field-annealed state. This behavior is also exhibited in the flux density versus field. Both curves have a significant impact on device design. The type (mechanical or magnetic) and magnitude of stored energy largely determines the optimum magnetic bias point and impacts operational efficiency.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Nt Magnetic annealing and temperature-hysteresis effects
75.30.Gw Magnetic anisotropy

Magnetocaloric effect in La0.5Pr0.5Fe11.5Si1.5 compounds with a combined addition of Co and C

Jun Shen and Jin-Liang Zhao

J. Appl. Phys. 111, 07A908 (2012); doi:10.1063/1.3670598 (3 pages)

Online Publication Date: 9 February 2012

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The influence of a combined addition of Co and C on the magnetocaloric effect in the La0.5Pr0.5Fe11.5Si1.5 compound is investigated. The addition of Co and C can adjust Curie temperature (TC) to around room temperature. Although the magnetic entropy change (ΔSM) of La0.5Pr0.5Fe11.5−xCoxSi1.5C0.2 decreases with the increase of x, the maximum hysteresis loss at TC reduces remarkably from 23.6 J/kg for x = 0 to close to zero for x = 0.2. For x = 0.8, the maximum value of ΔSM is −11.6 J/kg K with an RC value of 386 J/kg around TC = 295 K for a magnetic field change of 0-5 T. Our result reveals that a large ΔSM and a small hysteresis loss can be simultaneously achieved in NaZn13-type LaPrFeSi compounds with a combined addition of Co and C.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Reduction of hysteresis loss and large magnetocaloric effect in the C- and H-doped La(Fe, Si)13 compounds around room temperature

H. Zhang, B. G. Shen, Z. Y. Xu, X. Q. Zheng, J. Shen, F. X. Hu, J. R. Sun, and Y. Long

J. Appl. Phys. 111, 07A909 (2012); doi:10.1063/1.3670608 (3 pages)

Online Publication Date: 9 February 2012

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The effects of the interstitial C and H atoms on the phase formation, the hysteresis loss, and magnetocaloric effects of the NaZn13-type La(Fe, Si)13 compounds are investigated. It is found that the annealing time to obtain a 1:13 structure is significantly reduced from 40 days for LaFe11.7Si1.3 to a week for LaFe11.7Si1.3C0.2. The introduction of C and H atoms can adjust Curie temperature to around room temperature and leads to the decrease in magnetic entropy change (ΔSM) and magnetic hysteresis loss due to the weakening of itinerant-electron metamagnetic transition. Large −ΔSM of 19.0 J/kg K at room temperature without hysteresis loss for LaFe11.7Si1.3C0.2H1.7 is obtained for a field change of 5 T.
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75.30.Sg Magnetocaloric effect, magnetic cooling
61.72.jj Interstitials
81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetocaloric materials with first-order phase transition: thermal and magnetic hysteresis in LaFe11.8Si1.2 and Ni2.21Mn0.77Ga1.02 (invited)

K. P. Skokov, V. V. Khovaylo, K.-H. Müller, J. D. Moore, J. Liu, and O. Gutfleisch

J. Appl. Phys. 111, 07A910 (2012); doi:10.1063/1.3670987 (6 pages)

Online Publication Date: 10 February 2012

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This is a report on a comparative study of thermal and magnetic hysteresis in LaFe11.8Si1.2 and Ni2.21Mn0.77Ga1.02 polycrystalline samples near their first-order phase transitions by measurements of magnetization and direct measurements of the adiabatic temperature change, ΔTad(H). Based on the obtained M(T) and M(H) dependencies, H-T diagrams were constructed for both alloys and used to explain the ΔTad(H) dependencies. For low thermal hysteresis and a sharp transition in the temperature dependence of magnetization (LaFe11.8Si1.2), the field dependencies of ΔTad(H) are governed by the phase boundary between ferromagnetic and paramagnetic states. For large thermal hysteresis and a broad transition width in temperature (Ni2.21Mn0.77Ga1.02), the phase boundary has little impact on ΔTad(H). It is also shown that, in the phase transition region, ΔTad measured upon the first application of magnetic field (virgin ΔTad(H) leg) can differ from that measured upon subsequent runs of the field. This can lead to an overestimation of the magnetocaloric effect, if only the virgin leg of ΔTad(H) is considered.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.20.En Metals and alloys
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetovolume effect in Ho2Fe17-xMnx compounds

J. L. Wang, A. J. Studer, S. J. Kennedy, R. Zeng, S. X. Dou, and S. J. Campbell

J. Appl. Phys. 111, 07A911 (2012); doi:10.1063/1.3671422 (3 pages)

Online Publication Date: 13 February 2012

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The structural and magnetic properties of seven compounds in the Ho2Fe17-xMnx series (x = 0-5) have been investigated. The spontaneous magnetization Ms at 10 K exhibits a minimum at x ≈ 3.8 while the 3d-sublattice magnetization MT is found to decrease at ∼ −3.4 μB/per Mn atom compared with the rate of ∼−2.0 μB/per Mn atom expected from a simple dilution model. All of the Ho2Fe17-xMnx compounds exhibit anisotropic thermal expansion below their Curie temperatures leading to the presence of strong magnetovolume effects and Invar-type behavior below TC. An approximately zero volume thermal expansion has been detected between 10 K and 270 K for Ho2Fe17. The maximum magnetic entropy changes for Ho2Fe17-xMnx with x = 0 and 2.0 are 3.2 J kg−1 K−1 around TC ∼ 336 K and 2.7 J kg−1 K−1 around TC ∼ 302 K, respectively, for magnetic field change of B = 0-5 T.
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81.05.Bx Metals, semimetals, and alloys
65.40.De Thermal expansion; thermomechanical effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
back to top Biomedical and Molecular Magnets

Magnetic properties and microstructures of iron oxide@mesoporous silica core-shell composite for applications in magnetic dye separation

Weichang Hao, Yang Xi, Jingwei Hu, Tianmin Wang, Y. Du, and X. L. Wang

J. Appl. Phys. 111, 07B301 (2012); doi:10.1063/1.3670049 (3 pages)

Online Publication Date: 6 February 2012

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In this report, hollow mesoporous silica (HMS) and iron oxide-hollow mesoporous silica (FexOy@HMS) core-shell composite were prepared by a one-step facile fabrication method. Transmission electron microscopy, X-ray diffraction, N2 adsorption–desorption isotherms, and vibrating sample magnetometer were used to characterize the morphology, microstructure, and magnetic properties of the HMS and core-shell composite. The magnetic separability of FexOy@HMS core-shell composite was tested in Rhodamine B (Rh.B) dye solution. The results indicate that the core-shell composite can absorb Rh.B dyes molecules effectively up to 90.1%.
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75.75.Cd Fabrication of magnetic nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.43.Gt Powders, porous materials
68.43.Mn Adsorption kinetics
68.43.Nr Desorption kinetics
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