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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); http://dx.doi.org/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.
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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); http://dx.doi.org/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); http://dx.doi.org/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); http://dx.doi.org/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.
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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); http://dx.doi.org/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); http://dx.doi.org/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); http://dx.doi.org/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)

Well-isolated L10 FePt–SiNx–C nanocomposite films with large coercivity and small grain size

K. F. Dong, H. H. Li, Y. G. Peng, G. Ju, G. M. Chow, and J. S. Chen

J. Appl. Phys. 111, 07A308 (2012); http://dx.doi.org/10.1063/1.3671430 (3 pages)

Online Publication Date: 14 February 2012

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FePt–SiNx–C films on TiN/CrRu/glass substrate with large coercivity, (001) texture, and small isolated grains were obtained by co-sputtering FePt, Si3N4, and C targets at 380 °C. It was found that when C was doped into the FePt–SiNx films, the out-of-plane coercivity increased while the small in-plane coercivity remained unchanged. Grain size decreased and grain size distribution became more uniform with increasing the C doping concentration. The x-ray photoelectron spectroscopy (XPS) depth profile showed a uniform depth distribution of Si in the FePt layer. The Si2p XPS spectrum implied the existence of Fe–Si bonds, indicating that SiNx was located at the FePt grain boundaries and was stable against diffusion to the surface, thus favoring grain isolation. Well-isolated FePt (001) granular films with coercivity higher than 21.5 kOe and an average grain size of 5.6 nm were obtained by doping 40 vol. % of SiNx and 20 vol. % of C.
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68.55.A- Nucleation and growth
61.72.Mm Grain and twin boundaries
81.15.Cd Deposition by sputtering
81.16.-c Methods of micro- and nanofabrication and processing
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
85.40.Ry Impurity doping, diffusion and ion implantation technology

Continuous-annealing method for producing a flexible, curved, soft magnetic amorphous alloy ribbon

Bruno Francoeur and Pierre Couture

J. Appl. Phys. 111, 07A309 (2012); http://dx.doi.org/10.1063/1.3671431 (3 pages)

Online Publication Date: 14 February 2012

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A method has been developed for continuous annealing of an amorphous alloy ribbon moving forward at several meters per second, giving a curved shape to the ribbon that remains flexible afterward and can be easily wound into a toroidal core with excellent soft magnetic properties. A heat pulse was applied by a compact system on a Metglas 2605HB1 ribbon moving forward at 5 m/s to initiate a thermal treatment at 460 °C, near crystallization onset. The treatment duration was less than 0.1 s, and the heating and cooling rates were above 10 000 °C/s, which helped preserve most of the alloy as-cast ductility state. Such high temperature rates were achieved by forcing a static contact between the moving ribbon and a temperature-controlled roller. A tensile stress and a series of bending configurations were applied on the moving ribbon during the treatment to induce the development of magnetic anisotropy and to obtain the desired natural curvature radius. The core losses at 60 Hz of a toroidal test core wound with the resulting ribbon are lower than the specific values reported by the alloy manufacturer. This method can be implemented at the casting plant for supplying a low-cost, ready-to-use ribbon, easy to handle and cut, for mass production of toroidal cores for distribution transformer kernels (core and coil only), pulse power cores, etc.
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81.05.Kf Glasses (including metallic glasses)
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Nt Magnetic annealing and temperature-hysteresis effects
81.05.Bx Metals, semimetals, and alloys

Magnetocrystalline anisotropy in FePt with L10 ordering and tetragonal distortion

Yohei Kota and Akimasa Sakuma

J. Appl. Phys. 111, 07A310 (2012); http://dx.doi.org/10.1063/1.3671436 (3 pages)

Online Publication Date: 14 February 2012

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We evaluate the magnetocrystalline anisotropy energy of L10 type FePt alloys with the lattice distortion and atomic disorder by using the first-principles calculation, which adopts the tight-binding linear muffin-tin orbital method in conjunction with the coherent potential approximation techniques. The calculated result indicates that the magnetocrystalline anisotropy energy is quite sensitive to the mentioned factors. In particular, it is drastically decreased with the degree of ordering compared with the expected value from the completely ordered structure. We will suggest that the improvement of the chemical ordering of the L10 crystal is one of the significant points to obtain a large magnetocrystalline anisotropy from FePt compounds.
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75.30.Gw Magnetic anisotropy
75.40.Mg Numerical simulation studies
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Be Transition metals and alloys

Effect of P to B concentration ratio on soft magnetic properties in FeSiBPCu nanocrystalline alloys

Fanli Kong, He Men, Tiancheng Liu, and Baolong Shen

J. Appl. Phys. 111, 07A311 (2012); http://dx.doi.org/10.1063/1.3672082 (3 pages)

Online Publication Date: 16 February 2012

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The effects of P to B concentration ratio on magnetic properties and microstructure in annealed Fe82.65Si2B14−xPxCu1.35 (x = 1−6) soft magnetic alloys prepared by melt spinning were investigated. The proper substitution of B with P was found to be effective in decreasing grain size in the alloys annealed at 793 K for 120 s. The coercive force Hc markedly decreases from 67.1 to 1.1 A/m and the saturation magnetic flux density Bs shows a slightly decreasing trend with increasing P content from x = 1 to 5. The nanocrystalline Fe82.65Si2B9P5Cu1.35 alloy, with an average grain size of 15 nm, shows a combination of high Bs and excellent soft magnetic properties.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
81.40.Gh Other heat and thermomechanical treatments

Soft magnetic properties of bulk FeCoMoPCBSi glassy core prepared by copper mold casting

Mingxiao Zhang, Fanli Kong, Anding Wang, Chuntao Chang, and Baolong Shen

J. Appl. Phys. 111, 07A312 (2012); http://dx.doi.org/10.1063/1.3672088 (3 pages)

Online Publication Date: 16 February 2012

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Bulk Fe66Co10Mo3.5P10C4B4Si2.5 glassy core of 10 mm in outer diameter, 6 mm in inner diameter, and 1 mm in thickness was successfully prepared by copper mold casting. The effects of annealing treatments on magnetic properties and microstructure of these cores were investigated. After an optimum annealing treatment, the resulting bulk glassy core exhibits good magnetic properties, i.e., high saturation magnetic flux density of 1.23 T, low coercive force of 1.0 A/m, high maximum permeability of 450 000, respectively. In addition, the glassy core also shows low core loss of 0.4 W/kg at 50 Hz and at maximum magnetic flux density of 1 T. The synthesis of bulk glassy core with excellent magnetic properties is encouraging for enlarging the application field of ferromagnetic bulk glassy alloys.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
81.10.Fq Growth from melts; zone melting and refining
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.40.Gh Other heat and thermomechanical treatments

Dual phase transformation and resultant magnetic properties in Fe3Pt thin films

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

J. Appl. Phys. 111, 07A313 (2012); http://dx.doi.org/10.1063/1.3672405 (3 pages)

Online Publication Date: 16 February 2012

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Fifty-nm-thick Fe75Pt25 thin films have been made on glass substrates by rf magnetron sputtering at room temperature, and subsequently annealed at 300 –700 °C (Ta) for 1 h. The as-deposited Fe3Pt film exhibits high magnetization of 1530 emu/cm3 and a disordered bcc structure, confirmed by high-resolution synchrotron radiation x-ray diffractometry. First-phase transformation from the bcc to disorder fcc structure occurs for samples annealed at 300 °C. With increasing of Ta up to 375 °C, the film displays a nearly disordered fcc phase with low magnetization of 1083 emu/cm3. The fcc phase changes to ordered L12 structure for samples with Ta ≥ 400 °C. The highly ordered L12 phase with magnetization of 1270 emu/cm3 and coercivity of 66 Oe was obtained in Fe3Pt film at 700 °C-annealing.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Analysis of heating effects (magnetic hyperthermia) in FeCrSiBCuNb amorphous and nanocrystalline wires

C. Gómez-Polo, S. Larumbe, J. I. Pérez-Landazábal, and J. M. Pastor

J. Appl. Phys. 111, 07A314 (2012); http://dx.doi.org/10.1063/1.3672850 (3 pages)

Online Publication Date: 16 February 2012

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The induction heating effects in amorphous and nanocrystalline wires, Fe73.5-xCrxSi13.5Cu1B9Nb3 (x = 3, 7, and 10), are analyzed in this work. In these alloys, the Curie temperature of the amorphous phase, TC, can be tailored through the Cr content of the alloy or the volume crystalline fraction after nanocrystallization. Four samples were selected; amorphous with x = 0 and 10 and nanocrystalline x = 7 with different crystalline fractions. The Curie temperature of the residual amorphous phase, TCa, was experimentally determined by the temperature dependence of the self-inductance of the samples. The analysis of the frequency dependence of the complex magnetic susceptibility enabled the estimation of the magnetic power losses in the samples. The heating effects on the wires were analyzed under the application of an ac magnetic field employing a home-made hyperthermia set-up. A single piece of a wire was immersed in a water bath (initial temperature from 291 K to 325 K) and subjected to the ac magnetic field. The specific absorption rate (SAR) was estimated through the initial slope of the temperature increase as a function of time. Maximum SAR values were obtained in the amorphous sample (x = 3) with the highest TC and enhanced magnetic power losses. In the nanocrystalline samples (x = 7), the detected heating effects above TCa are interpreted as a consequence of the magnetization process of the ferromagnetic grains. However, in spite of the low SAR displayed by the amorphous wire with TC ≈ 300 K (x = 10), interesting self-regulated characteristics are observed in this sample.
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87.85.Rs Nanotechnologies-applications
87.19.Pp Biothermics and thermal processes in biology
87.50.C- Static and low-frequency electric and magnetic fields effects
87.85.J- Biomaterials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials

Development of a composite material with high magnetic permeability and low loss factor for high frequency application

Debangsu Roy and P. S. Anil Kumar

J. Appl. Phys. 111, 07A315 (2012); http://dx.doi.org/10.1063/1.3672867 (3 pages)

Online Publication Date: 16 February 2012

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A flexible composite suitable for MHz frequency application has been developed by combining Fe3O4 and polyvinyl alcohol (PVA). The loss factor and the permeability have been evaluated. At an optimum weight percentage of Fe3O4 in the PVA matrix, the frequency at which the loss factor gives a minimum shifts to the MHz region. The loss factor has been found to be lower by one order of magnitude at 70 MHz compared to the presently used nickel zinc ferrite. The Henkel plot and the Cole-Cole plot have been obtained for the understanding of the high magnetic permeability and the low loss factor.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

In-situ investigation of phase formation in nanocrystalline (Co97.5Fe2.5)89Zr7B4 alloy by high temperature x-ray diffraction

Samuel J. Kernion, Paul R. Ohodnicki, and Michael E. McHenry

J. Appl. Phys. 111, 07A316 (2012); http://dx.doi.org/10.1063/1.3673433 (3 pages)

Online Publication Date: 16 February 2012

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Crystallization and phase evolution in an (Co97.5Fe2.5)89Zr7B4 amorphous alloy was studied by high temperature x-ray diffraction (HTXRD) and transmission electron microscopy (TEM). Co-based nanocomposite alloys have zero magnetostriction and a strong response to magnetic field annealing making them interesting for sensor and high frequency power applications. Amorphous alloys, synthesized by single roll melt-spinning, develop a nanocomposite structure after primary crystallization. After annealing at 540 °C for 1 h, TEM images and diffraction patterns confirm a grain size of 19 nm and the presence of at least two phases. HTXRD results show preferential body centered cubic (bcc) nucleation and formation of multiple phases at various stages of crystallization. Only the face centered cubic (fcc) phase remained at temperatures above 600 °C. On heating, the lattice parameter of the fcc phase increases at a rate higher than expected from thermal expansion. This is partially explained by an increase in the Fe-concentration in fcc crystallites.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.80.+q Magnetomechanical effects, magnetostriction
81.07.Bc Nanocrystalline materials
64.70.dg Crystallization of specific substances

Effect of attrition time on the microwave permeability of magnetic Fe-Si-Al flakes

Mangui Han (韩满贵), Difei Liang (梁迪飞), Jianliang Xie (谢建良), and Longjiang Deng (邓龙江)

J. Appl. Phys. 111, 07A317 (2012); http://dx.doi.org/10.1063/1.3673813 (3 pages)

Online Publication Date: 16 February 2012

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Fe-Si-Al particles with irregular shapes have been successfully milled into flaky shapes by attrition for 10, 20, and 30 h, respectively. The attrition time has very small effect on the static magnetic properties, but shows strong effects on the high frequency properties (permittivity and permeability). With increasing the attrition time, the values of permeability can be obviously enhanced, especially at lower frequencies. The high frequency permittivity values of flakes milled for 30 h are much larger than those of particles milled for 10 or 20 h. A multiple relaxation processes model has been used to study the permeability dispersion behaviors. Analysis show the variation of shape anisotropy could be the main cause for the observed changes in permeability dispersion behaviors. However, the electromagnetic wave absorption properties of composites filled with these flaky shape Fe-Si-Al particles are found deteriorated when the particles have been milled for longer time.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
81.20.Wk Machining, milling
77.22.Ch Permittivity (dielectric function)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Tailoring magnetocrystalline anisotropy of FePt by external strain

Pavel V. Lukashev, Nathan Horrell, and Renat F. Sabirianov

J. Appl. Phys. 111, 07A318 (2012); http://dx.doi.org/10.1063/1.3673853 (3 pages)

Online Publication Date: 16 February 2012

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We propose using strain assisted reduction in anisotropy of FePt to control magnetization reversal in the writing on the magnetic storage devices. Our first-principles calculations show 21% decrease of the magnetocrystalline anisotropy energy (MAE) with application of 1.5% tensile biaxial strain. The reduction of MAE is primarily due to the change of the c/a ratio and to some extent due to the increase in volume. We propose building bilayer (or heterostructure) of FePt and piezoelectric film. This system is expected to allow the control of anisotropy constant by applying electric field to the system. Finally, we discuss the possibility of forming medium using bi-layer of FePt and soft magnetic material with the gradient of anisotropy constant.
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75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys

Electrodeposition and magnetic properties of FeCo alloy films

Dong Zhou, Mingge Zhou, Minggang Zhu, Xu Yang, and Ming Yue

J. Appl. Phys. 111, 07A319 (2012); http://dx.doi.org/10.1063/1.3675063 (3 pages)

Online Publication Date: 16 February 2012

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FeCo alloys thin films have been successfully electrodeposited on Ag films. The morphology, structure, composition, and magnetic property of the FeCo films were characterized by scanning electron microscopy, x-ray diffraction, induction-coupled plasma spectrometry, vibrating sample magnetometer and network analyzer. The use of reverse pulse current in the process of electrodepostion can reduce the surface roughness obviously. The effects of anodic current density and thickness are studied. The results show that the film fabricated under appropriate conditions has low coercivity and excellent high-frequency magnetic property.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
68.35.bd Metals and alloys
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Unusual magnetization characteristics of Fe-Ni films with graded composition

Leszek M. Malkinski, Rahmatollah Eskandari, April L. Fogel, and Seonggi Min

J. Appl. Phys. 111, 07A320 (2012); http://dx.doi.org/10.1063/1.3675065 (3 pages)

Online Publication Date: 16 February 2012

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Thin films of Fe-Ni with graded composition have been deposited on a Si (001) substrate at room temperature by co-sputtering of Fe and Ni with variable rates of the constituting elements. The composition of the films was changing linearly across the thickness from Fe80Ni20 to Fe6Ni94. Five samples were studied with the thickness of 30, 50, 100, 150, and 200 nm. The hysteresis loops measured with the field applied in the film plane had square shape and the coercivity was varying from 11 to 22 Oe. However, the loops for the field perpendicular to the film plane displayed unusual shapes consisting of a double-step hysteresis loop at low fields and unhysteretic part at higher fields. The size of the steps varied with the thickness of the film. The most likely source of the double step hysteretic curves was identified as magnetostrictive stresses at the film/substrate interface. This was evidenced by the disappearance of the second hysteresis step after annealing at 200 °C for 1 h and significant changes of the hysteresis loops when the same structure was deposited starting from Fe-rich or Ni-rich compositions at the substrate.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Cation distribution in nickel manganese oxide

S. L. Cheng, J. G. Lin, K. M. Kuo, and Gung Chern

J. Appl. Phys. 111, 07A321 (2012); http://dx.doi.org/10.1063/1.3675151 (3 pages)

Online Publication Date: 16 February 2012

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We use the technique of electron spin resonance (ESR) to analyze the distribution of cations in Mn3−xNixO4with x = 0–1. ESR data suggest that Ni2+ ions prefer to occupy octahedral-sites (B-sites) at low doping and concurrently produce a Mn4+ ion in B-site. As Ni2+ ions reach a critical value of 0.5, partial tetrahedral-sites are replaced by Mn3+ ions and form inverse spinel. Continually adding the Ni content up to x ∼ 1 results into a full transformation of structure into inverse spinel, which is accompanied with a drop of ESR intensities.
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76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
71.70.Ch Crystal and ligand fields
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Magnetism of BaB6 thin films synthesized by pulsed laser deposition

K. Ackland, M. Venkatesan, and J. M. D. Coey

J. Appl. Phys. 111, 07A322 (2012); http://dx.doi.org/10.1063/1.3675616 (3 pages)

Online Publication Date: 16 February 2012

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Amorphous BaB6 films synthesized by pulsed laser deposition show ferromagnetic-like signals for substrate temperatures in the range 450–550 °C. The magnetization is virtually anhysteretic, isotropic, and independent of temperature down to 4 K. Less than 4.5% of the volume fraction of the films is magnetically ordered, consistent with models where the magnetism is due to defects, interfaces, or grain boundaries.
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75.70.Ak Magnetic properties of monolayers and thin films
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High temperature x ray diffraction determination of the body-centered-cubic–face-centered-cubic transformation temperature in (Fe70Ni30)88Zr7B4Cu1 nanocomposites

J. J. Ipus, P. Herre, P. Ohodnicki, and M. E. McHenry

J. Appl. Phys. 111, 07A323 (2012); http://dx.doi.org/10.1063/1.3675990 (3 pages)

Online Publication Date: 16 February 2012

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In situ high-temperature x ray diffraction and magnetization measurements were performed on a melt-spun (Fe70Ni30)88Zr7B4Cu1 amorphous alloy to follow its structural evolution. At 728 K, a bcc-FeNi phase was observed as the primary crystallization product followed by transformation to an fcc phase ∼773 K. During cooling to room temperature, the fcc-to-bcc transformation was not observed, and the metastable fcc-NiFe phase was retained at room temperature.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Rs Electrical and magnetic properties related to treatment conditions
61.43.Dq Amorphous semiconductors, metals, and alloys
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.66.Dk Alloys
81.05.Bx Metals, semimetals, and alloys

Fabrication of L10-MnAl perpendicularly magnetized thin films for perpendicular magnetic tunnel junctions

Masaki Hosoda, Mikihiko Oogane, Miho Kubota, Takahide Kubota, Haruaki Saruyama, Satoshi Iihama, Hiroshi Naganuma, and Yasuo Ando

J. Appl. Phys. 111, 07A324 (2012); http://dx.doi.org/10.1063/1.3676428 (3 pages)

Online Publication Date: 16 February 2012

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Structural and magnetic properties of MnAl thin films with different composition, growth temperature, and post-annealing temperature were investigated. The optimum condition for fabrication of L10-MnAl perpendicularly magnetized thin film deposited on Cr-buffered MgO single crystal substrate was revealed. The results of x ray diffraction indicated that the MnAl films annealed at proper temperature had a (001)-orientation and L10-ordered structure. The L10-ordered films were perpendicularly magnetized and had a large perpendicular anisotropy. In addition, low surface roughness was achieved. For the optimized fabrication condition, the saturation magnetization Ms of 600 emu/cm3 and perpendicular magnetic anisotropy Ku of 1.0 × 107 erg/cm3 was obtained using the Mn48Al52 target at deposition temperature of 200 °C and post-annealing temperature of 450 °C.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
68.35.bd Metals and alloys
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Temperature dependent magnetization in Co-base nanowire arrays: Role of crystalline anisotropy

L. G. Vivas, M. Vázquez, V. Vega, J. García, W. O. Rosa, R. P. del Real, and V. M. Prida

J. Appl. Phys. 111, 07A325 (2012); http://dx.doi.org/10.1063/1.3676431 (3 pages)

Online Publication Date: 16 February 2012

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Co, Co(1−x)Pdx, and Co(1−y)Niy nanowire arrays have been prepared by electrochemical template-assisted growth. Hcp, fcc or both phases are detected in Co nanowires depending on their length (300 nm to 40 μm) and on the content of Pd (0 ≤ x ≤ 0.4) and Ni (0 ≤ y ≤ 0.8). Their magnetic behavior has been studied under longitudinal and perpendicular applied fields. The effective magnetic anisotropy is mostly determined by the balance between the shape and the crystalline terms, the latter depending on the fractional volume of hcp phase with strong perpendicular anisotropy and fcc phase with weaker longitudinal anisotropy. The temperature dependence of remanence and coercivity and the eventual observation of compensation temperature is interpreted as due to the different temperature dependence of shape and hcp crystalline anisotropy. Optimum longitudinal magnetic anisotropy is achieved in low Pd-content CoPd nanowires and in short Co nanowires.
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75.75.-c Magnetic properties of nanostructures
75.78.-n Magnetization dynamics
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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