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1 May 2007

Volume 101, Issue 9, Articles (09xxxx)

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back to top Ferrites, Garnets, and Microwave Materials

Low-loss barium ferrite quasi-single-crystals for microwave application

Yajie Chen, Anton L. Geiler, Taiyang Chen, Tomokazu Sakai, C. Vittoria, and V. G. Harris

J. Appl. Phys. 101, 09M501 (2007); http://dx.doi.org/10.1063/1.2709726 (3 pages) | Cited 14 times

Online Publication Date: 27 March 2007

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Barium hexaferrites (BaFe12O19) are especially useful for microwave/millimeter devices. Due to large ferromagnetic resonance (FMR) loss (linewidths >2 kOe), traditional compacts of polycrystalline Ba ferrites indeed hinder the utilization of the materials for practical devices. The present experiment demonstrates that the quasi-single-crystal Ba ferrite disks can be fabricated by a single solid-state reaction technique without liquid phase participation, combining with a processing of alignment for the ferrite seed crystals. The ferrite bulks show a pure hexagonal Ba ferrite phase, an expected 4πMs of 4.48 kG, and coercivity of 10 ∼ 20 Oe along the c axis, similar to the results of a typical single crystal. The FMR measurement indicates that the sample yields an anisotropy field of 16.0 kOe and a linewidth of about 300 Oe at U-band frequencies. Although the linewidth is broader than ideal Ba ferrite single crystals (ΔH<100 Oe), it may be possible to reduce to 100 Oe by eliminating pores, cracks, local grain boundary, and nonuniformity. In terms of material preparation, we believe that it is cost effective in the production of future microwave devices.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Spin sprayed Ni(–Zn)–Co ferrite films with natural resonance frequency exceeding 3 GHz

Koichi Kondo, Shigeyoshi Yoshida, Hiroshi Ono, and Masanori Abe

J. Appl. Phys. 101, 09M502 (2007); http://dx.doi.org/10.1063/1.2710465 (3 pages) | Cited 16 times

Online Publication Date: 2 April 2007

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Magnetic films having in the gigahertz range high real permeability μ′ and yet exhibiting weak imaginary permeability μ″ (thus low in tan δ = μ″/μ′) are in great need recently, for use in next-generation magnetic devices such as radio frequency identification (RFID) tags utilizing 900 MHz or 2.45 GHz band. In this study we successfully prepared films (composition: Ni0.23±0.01ZnxCoyFe2.76±0.01−x−y, x = 0–0.34 and y = 0.23–0.27) which exhibit such highly capable complex permeability spectra. They were prepared from an aqueous solution at 90 °C by spin spray ferrite plating. The films are very low in magnetic losses, having tan δ = 0.05–0.14 even at 900 MHz, because they have high natural resonance frequencies, fr = 3.3–5.4 GHz. The tan δ is much lower than that (>0.4) observed for composite-type magnetic sheets at 900 MHz. Transmission characteristics of 900 MHz band RFID tags were prominently improved by placing the ferrite films of 3 μm thickness on the tags.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Structure, magnetism, and tunable microwave properties of pulsed laser deposition grown barium ferrite/barium strontium titanate bilayer films

R. Heindl, H. Srikanth, S. Witanachchi, P. Mukherjee, T. Weller, A. S. Tatarenko, and G. Srinivasan

J. Appl. Phys. 101, 09M503 (2007); http://dx.doi.org/10.1063/1.2710467 (3 pages) | Cited 6 times

Online Publication Date: 2 April 2007

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Ferrite/ferroelectric films are of interest as they afford dual tunability of the permeability and permittivity using magnetic and electric fields. We have grown bilayered thin films of ferrimagnetic BaFe12O19 (BaM) and ferroelectric Ba0.5Sr0.5TiO3 (BST) on A-oriented polished sapphire substrates using pulsed laser deposition. X-ray thin film analysis (θ-2θ and azimuthal scans) established highly oriented crystalline films. Magnetic hysteresis loops indicated large magnetic anisotropy between the in-plane and out-of-plane field orientations and the M-H characteristics of BaM were influenced by the presence of the BST layer. Electrical and magnetic tunability studies of the bilayers in the frequency range of 1–65 GHz are also reported.
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75.50.Gg Ferrimagnetics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.30.+q High-frequency effects; plasma effects

A simple process for ferrite film preparation from one solution without using hazardous oxidizing agent

A. K. Subramani, N. Matsushita, T. Watanabe, M. Tada, M. Abe, and M. Yoshimura

J. Appl. Phys. 101, 09M504 (2007); http://dx.doi.org/10.1063/1.2709753 (3 pages) | Cited 6 times

Online Publication Date: 4 April 2007

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A process for ferrite film preparation using an aqueous solution was developed and named as “one solution spray technique” (OSST). Highly crystallized spinel ferrite films can be prepared by spraying only one solution at a very low temperature of 90 °C without any postannealing. In contrast to the conventional spray technique (CST), two solutions (reaction solution and an oxidizing solution containing pH buffer) were independently sprayed. In OSST, reaction solution containing a mixture of FeCl2, CH3COOK, and urea was used. The Fe3O4 films prepared by OSST exhibited a real permeability of μ′ = 35 and a very high resonance frequency of fr = 1.25 GHz, which was superior to that for films prepared by CST (fr = 850 MHz). The μ″×f spectra, which are proportional to the noise suppression effect of the films, proved that the films prepared by this technique have suitable properties to be used as conducted noise suppressors in the gigahertz range.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Rs Spray coating techniques
68.55.A- Nucleation and growth

Permeability of submicron and nanometer ferromagnetic particle composites

Y. Shimada, M. Yamaguchi, G. W. Qin, S. Okamoto, and O. Kitakami

J. Appl. Phys. 101, 09M505 (2007); http://dx.doi.org/10.1063/1.2712019 (3 pages) | Cited 6 times

Online Publication Date: 9 April 2007

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Ferromagnetic particle composites which include submicron and nanometer particles with large size difference exhibit higher permeability than the assembly of the pure composite constituent. The particles are redistributed in a magnetic field to reduce the demagnetizing field in the process of composite formation by heating. In this report composites of Fe and Permalloy particles were studied. Permeability is appreciably enhanced for the composites in spite of very low permeability for Permalloy particles. Further improvement is expected by developing fabrication process of particles with higher dispersion and higher saturation magnetization.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials

Magnetic properties of nanoparticles of CoxFe(3−x)O4 (0.05 ⩽ x ⩽ 1.6) prepared by combustion reaction

Adolfo Franco Júnior, Vivien Zapf, and Paul Egan

J. Appl. Phys. 101, 09M506 (2007); http://dx.doi.org/10.1063/1.2711063 (3 pages) | Cited 10 times

Online Publication Date: 9 April 2007

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Nanoparticles of CoxFe(3−x)O4 with x ranging from 0.05 to 1.6 were synthesized by a combustion reaction method using iron nitrate, cobalt nitrate, and urea as fuel. X-ray diffraction patterns of all systems showed broad peaks consistent with the cubic inverse spinel structure of cobalt ferrite. The absence of extra reflections in the diffraction patterns of as-prepared materials, with x = 0.6, 0.8, and 1.0, demonstrates the phase purity. Magnetization measurements show that the saturation magnetization (Ms), coercivity (Hc), and remanent magnetization (Mr) depend on the molar cobalt concentration and the temperature as well. At 4 K, the reduced remanence, Mr/Ms, are equal to 0.66 and 0.63 for x = 0.8 and 1.0, respectively, indicating that cubic-type magnetic anisotropy is significant in these nanoparticles. These observations are discussed in terms of a model in which it is assumed that each crystallite consists of a ferromagnetic core surrounded by a magnetically disordered shell.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.Be Chemical synthesis methods
61.66.Bi Elemental solids
61.66.Dk Alloys
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Misorientations in [001] magnetite thin films studied by electron backscatter diffraction and magnetic force microscopy

A. Koblischka-Veneva, M. R. Koblischka, J. D. Wei, Y. Zhou, S. Murphy, F. Mücklich, U. Hartmann, and I. V. Shvets

J. Appl. Phys. 101, 09M507 (2007); http://dx.doi.org/10.1063/1.2709424 (3 pages) | Cited 3 times

Online Publication Date: 10 April 2007

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Magnetite thin films grown on [001] oriented MgO substrates are analyzed by means of electron backscatter diffraction (EBSD) analysis and magnetic force microscopy in applied fields. The EBSD technique enables the crystallographic orientation of individual grains to be determined with a high spatial resolution up to 20 nm on such ceramic samples. A high image quality of the recorded Kikuchi patterns was achieved enabling multiphase scans and high spatial resolution measurements. Upon annealing in air, the magnetic properties of the magnetite thin films were found to change considerably. Using the EBSD analysis, we find that misoriented grains remaining after the annealing step form small islands with a size of about 100 nm. The size and distribution of these islands correspond well to the observations of antiferromagnetic pinning centers within the magnetic domain structures carried out by magnetic force microscopy on the same samples.
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68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Ee Antiferromagnetics
79.20.Kz Other electron-impact emission phenomena
81.40.Gh Other heat and thermomechanical treatments

High-resistivity nanogranular Co–Al–O films for high-frequency applications

Pedram Khalili Amiri, Yan Zhuang, Hugo Schellevis, Behzad Rejaei, Marina Vroubel, Yue Ma, and Joachim N. Burghartz

J. Appl. Phys. 101, 09M508 (2007); http://dx.doi.org/10.1063/1.2710235 (3 pages)

Online Publication Date: 16 April 2007

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This work presents a series of high-resistivity nanogranular Co–Al–O films with maximum resistivity of ∼ 110 mΩ cm. The films were deposited using pulsed dc reactive sputtering of a Co72Al28 target in an oxygen/argon ambient. The samples were characterized by scanning electron microscopy (SEM), M-H loop measurements, and s-parameter measurements on microstrip transmission lines with Co–Al–O magnetic cores. The high-frequency magnetic permeability profile was extracted from the microstrip measurements. Reduction of deposition power resulted in resistivity enhancement, as well as reduction of coercivity and permeability. SEM images reveal an average grain size of ∼ 80 nm for films with the highest resistivity.
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73.61.Le Other inorganic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Size dependent magnetic properties and cation inversion in chemically synthesized MnFe2O4 nanoparticles

C. N. Chinnasamy, Aria Yang, S. D. Yoon, Kailin Hsu, M. D. Shultz, E. E. Carpenter, S. Mukerjee, C. Vittoria, and V. G. Harris

J. Appl. Phys. 101, 09M509 (2007); http://dx.doi.org/10.1063/1.2710218 (3 pages) | Cited 5 times

Online Publication Date: 18 April 2007

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MnFe2O4 nanoparticles with diameters ranging from about 4 to 50 nm were synthesized using a modified coprecipitation method. X-ray diffractograms revealed a pure phase spinel ferrite structure for all samples. Transmission electron microscopy showed that the particles consist of a mixture of both spherical (smaller) and cubic (larger) particles dictated by the reaction kinetics. The Néel temperatures (TN) of MnFe2O4 for various particle sizes were determined by using high temperature magnetometry. The ∼ 4 nm MnFe2O4 particles showed a TN of about 320 °C whereas the ∼ 50 nm particles had a TN of about 400 °C. The high Néel temperature, compared with the bulk MnFe2O4 TN of 300 °C, is due to a change in cation distribution between the tetrahedral and octahedral sites of the spinel lattice. Results of extended x-ray absorption fine structure measurements indicate a systematic change in the cation distribution dependent on processing conditions.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.70.Dm X-ray absorption spectra
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Epitaxial growth of PbFe12O19 thin films by alternating target laser ablation deposition of Fe2O3 and PbO

A. L. Geiler, Y. He, S. D. Yoon, A. Yang, Y. Chen, V. G. Harris, and C. Vittoria

J. Appl. Phys. 101, 09M510 (2007); http://dx.doi.org/10.1063/1.2710222 (3 pages) | Cited 4 times

Online Publication Date: 19 April 2007

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Oriented M-type hexaferrite thin films are deposited using the alternating target laser ablation deposition (ATLAD) technique utilizing PbO and Fe2O3 targets. Crystallographic, dc magnetic, and microwave characterization results confirming the presence of a hexagonal PbFe12O19 phase are presented. We conclude that the ATLAD technique holds great promise for layer by layer deposition of various hexaferrite materials, the properties of which can be adjusted by varying the composition of the targets as well as the number of laser shots from each target during the deposition process. This would provide control over the uniaxial anisotropy fields and saturation magnetization values that was not possible in the conventional single target LAD technique.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

Magnetic and electromagnetic evaluation of the magnetic nanoparticle filled polyurethane nanocomposites

Zhanhu Guo, Sung Park, H. Thomas Hahn, Suying Wei, Monica Moldovan, Amar B. Karki, and David P. Young

J. Appl. Phys. 101, 09M511 (2007); http://dx.doi.org/10.1063/1.2711074 (3 pages) | Cited 30 times

Online Publication Date: 1 May 2007

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The magnetic and electromagnetic wave absorption behavior of a flexible iron-nanoparticle reinforced polyurethane nanocomposite is reported. Surface-initiated-polymerization (SIP) method was utilized to fabricate high-quality nanocomposites with uniform particle distribution and tunable particle loading (up to 65 wt %). The enhancement of coercive force is observed when the nanoparticles are embedded into the polymer matrix. Electromagnetic wave absorption performance at a discrete frequency as studied by metal-backed reflection loss indicates that the SIP nanocomposites can save the weight up to 50% compared to the composite counterpart with micron-size particles.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effects of bismuth substitution on Tb3−xBixFe5O12

Il. Jin Park and Chul Sung Kim

J. Appl. Phys. 101, 09M512 (2007); http://dx.doi.org/10.1063/1.2711394 (3 pages)

Online Publication Date: 2 May 2007

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The crystallographic and magnetic properties of Tb3−xBixFe5O12 (x = 0.5, 0.75, 1.0, and 1.25) powders were studied using x-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The crystal structure of the samples is determined to be normal cubic structure Ia3d by Rietveld refinement. The temperature dependence of magnetization with increasing bismuth concentration from x = 0.5 to x = 1.25 showed the decrease of compensation temperature from 177 to 107 K. Moreover, the field-cooled magnetizations of all samples show negative magnetization below the compensation temperature. We suggest that the negative magnetization is related to the local anisotropy by the strong covalent interaction between bismuth and iron. The isomer shifts obtained from Mössbauer spectra at room temperature of the (16a) and (24d) sites are about 0.26 and 0.04 mm/s, respectively, for all samples, which means that the irons at the (24d) site have a strong covalent interaction with bismuth. The Néel temperature increased from 616 to 655 K with increase of bismuth concentration from x = 0.5 to x = 1.25. Also, the saturation magnetization at room temperature increases linearly with increase of bismuth concentration. These behaviors can be explained by strong exchange interaction between a and d sublattices with increase of bismuth concentration.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Crystallographic and Mössbauer studies of Li0.5Fe2.5O4 prepared by high temperature thermal decomposition and sol-gel methods

Sung Wook Hyun and Chul Sung Kim

J. Appl. Phys. 101, 09M513 (2007); http://dx.doi.org/10.1063/1.2712524 (3 pages) | Cited 1 time

Online Publication Date: 3 May 2007

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Li0.5Fe2.5O4 powders were prepared by high temperature thermal decomposition (HTTD) and sol-gel methods. The sample prepared by HTTD method (SA) has space group of Fd3m. The samples annealed at 700 °C (SB) and quenched at 1000 °C (SC) prepared by sol-gel method have space groups of P4332 and Fd3m, respectively. The saturation magnetizations (Ms) for the sample prepared by HTTD method (SA) at room temperature is 55 emu/g and those for the samples annealed at 700 °C (SB) and quenched at 1000 °C (SC) prepared by sol-gel method are 59 and 62 emu/g, respectively. In contrast, the coercivity (Hc) values of the each sample are 4.1, 93.7, and 9.1 Oe, respectively. Mössbauer spectra of each sample have been obtained from 4.2 to 700 K. The valence state of Fe ions for the tetrahedral (A) and octahedral (B) sites is Fe3+. Mössbauer spectrum of the sample prepared by HTTD method shows superparamagnetic behavior at room temperature, while in case of sol-gel method, Mössbauer spectra show ferrimagnetic state of six line having the hyperfine field (Hf) values of 518 kOe for the A sites and 536 kOe for the B sites.
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61.66.Fn Inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
76.80.+y Mössbauer effect; other γ-ray spectroscopy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
75.50.Tt Fine-particle systems; nanocrystalline materials

The influence of cobalt population on the structural properties of CoxFe3−xO4

F. Nakagomi, S. W. da Silva, V. K. Garg, A. C. Oliveira, P. C. Morais, A. Franco Júnior, and E. C. D. Lima

J. Appl. Phys. 101, 09M514 (2007); http://dx.doi.org/10.1063/1.2712821 (3 pages) | Cited 23 times

Online Publication Date: 3 May 2007

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CoxFe3−xO4-based (x = 0.05–1.6) nanoparticles prepared by combustion reaction were investigated using x-ray diffraction, Raman spectroscopy, and Mössbauer spectroscopy. The Mössbauer data revealed Co2+ in both tetrahedral (site A) and octahedral (site B) sites of the cubic ferrite structure. For x ⩽ 0.4 the experimental data indicated the synthesis of a core-shell structure, with hematite as the shell and cobalt ferrite as the core of the nanoparticle. Differences in crystalline structure between the two phases support the evidences we found of a highly stressed core-shell interface, leading to symmetry reduction of the tetrahedral and octahedral sites.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.Be Chemical synthesis methods
82.33.Vx Reactions in flames, combustion, and explosions
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Hv Other nonmetallic inorganics
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Effects of cation distribution for AFeO3 (A = Ga,Al)

Woochul Kim, Jee Hoon We, Sam Jin Kim, and Chul Sung Kim

J. Appl. Phys. 101, 09M515 (2007); http://dx.doi.org/10.1063/1.2712819 (3 pages) | Cited 9 times

Online Publication Date: 3 May 2007

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Piezoelectric and ferrimagnetic AFeO3 (A = Ga,Al) samples have been prepared by various annealing conditions and then their hyperfine structures have been investigated by x-ray diffraction and Mössbauer spectroscopy. From the analysis of the x-ray diffraction patterns by Rietveld refinement method, the crystal structure of samples was found to be an orthorhombic structure (Pc21n,Pna21) with four different cation sites which are labeled A1 and A2 (predominantly occupied by gallium and aluminum ions) and Fe1 and Fe2 (predominantly occupied by Fe ion). The crystal structure is not changed between the samples, but the occupancies of Fe ions in four cationic sites show slight difference. We notice that the occupancies of Fe ion in A1 tetrahedral site of the samples have an effect on the magnetic properties. From the x-ray diffraction results, the ratios of occupied Fe ions in A1 site were determined to be 9.0%, 9.5%, and 7.8% for slow-cooled GaFeO3, quenched GaFeO3, and AlFeO3, respectively, which accord with the result of Mössbauer spectroscopy. We found that the Néel temperature range decreases from 265 to 250 K, with decreasing the Fe–O–Fe bond angles between GaFeO3 and AlFeO3. Also, external field dependence of magnetic moment curve shows a several-stepped shape which is similar with the exchange-spring magnet. It could be explained distinctly by an effect of Fe ion distribution in hyperfine structure.
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61.66.Fn Inorganic compounds
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Reduced magnetization in magnetic oxide nanoparticles

T. Kim and M. Shima

J. Appl. Phys. 101, 09M516 (2007); http://dx.doi.org/10.1063/1.2712825 (3 pages) | Cited 12 times

Online Publication Date: 4 May 2007

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Magnetic oxide nanoparticles have been studied to elucidate the effects of nanoscale finite size on the magnetic behavior of the particles. Magnetite nanoparticles synthesized by coprecipitation show superparamagnetism at room temperature with reduced saturation magnetization MS. The MS value decreases and approaches zero with decreasing particle size. Yttrium iron garnet (YIG) nanoparticles also show a similar trend. The magnetization of nanoparticles estimated using the Langevin function with the particle size distribution indicates that the reduced magnetization can be consistently explained by the existence of a spin-disordered surface layer with the thickness of 1–2 nm. The results found in magnetite and YIG nanoparticles suggest that the reduced magnetization can be commonly observed among magnetic oxide nanoparticles due to the existence of spin disordered surface layer.
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75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Effect of growth temperature on the magnetic, microwave, and cation inversion properties on NiFe2O4 thin films deposited by pulsed laser ablation deposition

C. N. Chinnasamy, S. D. Yoon, Aria Yang, Ashish Baraskar, C. Vittoria, and V. G. Harris

J. Appl. Phys. 101, 09M517 (2007); http://dx.doi.org/10.1063/1.2714204 (3 pages) | Cited 9 times

Online Publication Date: 7 May 2007

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First principles band structure calculations suggest that the preferential occupation of Ni2+ ions on the tetrahedral sites in NiFe2O4 would lead to an enhancement of the exchange integral and subsequently the Néel temperature and magnetization. To this end, we have deposited NiFe2O4 films on MgO substrates by pulsed laser deposition. The substrate temperature was varied from 700 to 900 °C at 5 mTorr of O2 pressure. The films were annealed at 1000 °C for different times prior to their characterization. X-ray diffraction spectra showed either (100) or (111) orientation with the spinel structure dependent on the substrate orientation. Magnetic studies showed a magnetization value of 2.7 kG at 300 K. The magnetic moment was increased to the bulk value as a result of postdeposition annealing at 1000 °C. The as produced films show that the ferromagnetic resonance linewidth at 9.61 GHz was 1.5 kOe, and it was reduced to 0.34 kOe after postannealing at 1000 °C. This suggests that the annealing led to the redistribution of Ni2+ ions to their equilibrium octahedral sites. Further, it is shown that the magnetically preferred direction of Ha can be aligned perpendicular to the film plane when films are grown with a fixed oxygen pressure of 5 mTorr for films deposited at 700 and 900 °C.
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75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Control of the cation occupancies of MnZn ferrite synthesized via reverse micelles

M. D. Shultz, M. J. Allsbrook, and E. E. Carpenter

J. Appl. Phys. 101, 09M518 (2007); http://dx.doi.org/10.1063/1.2713694 (3 pages) | Cited 9 times

Online Publication Date: 8 May 2007

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Variations in cation occupancy in mixed metal ferrite systems can affect their electronic and magnetic properties. It is known that different synthesis parameters can lead to various cation distributions and the ability to tune these distributions is of great interest. This study uses the extended x-ray-absorption fine structure–IR relationship to investigate the effect of various Fe2+/Fe3+ ratios in initial synthesis conditions on cation distribution for manganese zinc ferrite (MZFO). Differences in the precipitated material before firing could lead to differences in the final material if fired under similar conditions. This work uses several different ratios of Fe3+/Fe2+, which will affect the initial cell potential for the reaction, to synthesize nano MZFO. All samples were fired for 5 h at 500 °C under flowing nitrogen. Transmission electron microscopy micrographs reveal highly crystalline uniform nanoparticles of 16±2 nm. The x-ray diffraction revealed single phase crystalline MZFO with an average crystallite size of around 14 nm. The saturation magnetization ranged from 43 to 68 emu/g as measured by vibrating-sample magnetometry. The Fourier transform infrared (FTIR) analysis was used to determine the cation occupancies while changing the initial Fe3+/Fe2+ ratios from 10/90 to 90/10. The FTIR spectra revealed a shift in the first absorption region in the far IR from 566.98 to 549.62 cm−1 corresponding to the octahedral occupancies. This shift corresponds to a change in the percentage of octahedral sites occupied by manganese from roughly 25% to 12%. This change in manganese occupancy is also observed in the iron occupancies, which in turn help to explain the variation in saturation magnetization.
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81.07.Bc Nanocrystalline materials
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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)

Pulsed laser ablation deposition of nanocrystalline exchange-coupled Ni11Co11Fe67−xZr7B4Cux (x = 0,1) films for planar inductor applications

Ashish K. Baraskar, Soack Dae Yoon, Anton Geiler, Aria Yang, C. N. Chinnasamy, Yajie Chen, Nian Sun, Carmine Vittoria, Ramasis Goswami, Matthew Willard, and Vincent G. Harris

J. Appl. Phys. 101, 09M519 (2007); http://dx.doi.org/10.1063/1.2712055 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2007

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Nanocrystalline films of the Ni11Co11Fe67−xZr7B4Cux (x = 0,1) composition were deposited on fused quartz substrates by pulsed laser deposition. For the films of Ni11Co11Fe66Zr7B4Cu, the bcc grain size ranged from 5 to 8 nm in the films deposited at substrate temperatures from ambient to 300 °C. Films grown at a substrate temperature of 300 °C were found to have optimal magnetic properties including minima in the coercivity and ferromagnetic resonance (FMR) linewidth. The magnetic characterization studies showed coercivity Hc<5 Oe, 4πMS ∼ 16 kG, and in-plane uniaxial anisotropy field (HA) ∼ 25–30 Oe. The ferromagnetic resonance linewidth was measured to be 34 Oe and zero magnetic field ferromagnetic resonance at ∼ 2 GHz. These properties allow these films to be candidates for magnetic planar inductors operating from 0.5 to 2 GHz.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy

Microwave electromagnetic and absorption properties of Nd2Fe14B/α-Fe nanocomposites in the 0.5–18 and 26.5–40 GHz ranges

Li-Xian Lian, L. J. Deng, M. Han, W. Tang, and Shao-Dong Feng

J. Appl. Phys. 101, 09M520 (2007); http://dx.doi.org/10.1063/1.2712957 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2007

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Nd2Fe14B/α-Fe nanocomposites were prepared using a melt-spinning method, subsequent annealing treatment, and ball milling. The complex permittivity and permeability of the composites were measured in the 0.5–18 and 26.5–40 GHz frequency ranges. The permeability spectra of the Nd2Fe14B/α-Fe nanocomposites exhibit relaxation and resonance type characteristic in the 0.5–18 and 26.5–40 GHz frequency ranges, respectively. The resonance frequency (fr) of Nd10Fe78Co5Zr1B6 nanocomposite is 30 GHz due to the large anisotropy field (HA). However, the resonance frequency of the Nd2Fe14B/α-Fe sample is lower than that of Nd2Fe14B, due to the decrease of HA induced by the exchange interaction between hard and soft magnetic phases. These samples also showed good microwave absorption performance (reflection loss: <−20 dB) in 9, 17, and 35–38 GHz with matching thicknesses of 2, 1.2, and 0.37 mm, respectively. Therefore, Nd2Fe14B/α-Fe nanocomposites are thought to be a potential candidate for thinner microwave absorbers not only in the centimeter wave but also in the millimeter wave band.
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75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Magnetic anisotropy and crystalline texture in BaO(Fe2O3)6 thin films deposited on GaN/Al2O3

P. R. Ohodnicki, K. Y. Goh, Y. Hanlumyuang, K. Ramos, M. E. McHenry, Z. Cai, K. Ziemer, H. Morkoc, N. Biyikli, Z. Chen, C. Vittoria, and V. G. Harris

J. Appl. Phys. 101, 09M521 (2007); http://dx.doi.org/10.1063/1.2712295 (3 pages) | Cited 6 times

Online Publication Date: 11 May 2007

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BaO(Fe2O3)6 (BaM) thin films were deposited by pulsed laser deposition on GaN/Al2O3 substrates. A pole figure obtained from the (006) reflection indicated that ∼ 81% of the film volume had the c axis tilted less than 5° from the film normal. A low anisotropy field was inferred from vector coil vibrating sample magnetometer (VVSM) measurements. The reduction in Ha from literature values and a two-step switching of the easy axis magnetization is postulated to result from interdiffusion and misalignment effects. To alleviate interdiffusion and to improve the c-axis alignment, experiments were repeated with lower deposition temperatures, thinner films, and MgO buffer layers. The features of the hysteresis loop due to two-step switching and the in-plane coercivity were reduced while the anisotropy field (Ha) was larger. Films deposited with MgO buffer layers are observed to have single-step switching of the easy axis magnetization, larger anisotropy fields, and sharp ferromagnetic resonance (FMR) peaks. Films with MgO buffer layers were determined to have anisotropy fields Ha = 1.57 T by FMR and Ha ∼ 1.5–1.6 T as determined from the difference in the saturation fields for the easy and hard axis loops.
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75.50.Gg Ferrimagnetics
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
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Magnetic loss in soft ferrites

Waseem A. Roshen

J. Appl. Phys. 101, 09M522 (2007); http://dx.doi.org/10.1063/1.2712056 (3 pages) | Cited 2 times

Online Publication Date: 14 May 2007

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In order to understand the anomalous magnetic field dependence of the high frequency (200 kHz–1.0 MHz) losses, we consider the high field conductivity of the soft ferrites. We show that the high field conductivity is highly nonlinear. Separately, we show that this nonlinear behavior is due to tunneling between adjacent ferrite grains. In this paper we show that this tunneling based nonlinear conductivity gives rise to a different eddy current loss, which can explain the anomalous magnetic field dependence of the measured high frequency loss.
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75.60.-d Domain effects, magnetization curves, and hysteresis
75.50.Gg Ferrimagnetics
72.80.Sk Insulators

The magnetic properties of strained and relaxed Fe3−xMgxO4 ferrite films on MgO(001) and SrTiO3(001) by molecular beam epitaxy

D. S. Lee, J. S. Wang, Dilip K. Modak, Y. S. Liu, C. L. Chang, and G. Chern

J. Appl. Phys. 101, 09M523 (2007); http://dx.doi.org/10.1063/1.2712826 (3 pages) | Cited 4 times

Online Publication Date: 14 May 2007

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The present study grows a series of Fe3−xMgxO4 (0≦x≦1.5) films and systematically measure both structure and magnetization of these films. These films are grown on MgO and SrTiO3 (STO), which have small ( ∼ −0.3%) and large ( ∼ 7.5%) lattice mismatch in order to have either strained or relaxed films, by plasma-oxygen-assisted molecular beam epitaxy, respectively. X-ray diffraction (XRD) is carried out to analyze the crystalline structure. Saturation magnetization (Ms) of pure Fe3O4 (x = 0) on both substrates is ∼ 500 emu/cm3, which is consistent with the bulk value. However, Ms has a fast decrease with increasing x for the films grown on MgO(001), from 340 to  ∼ 100 emu/cm3 in the region of 0.3<x<1.35, and stays at ∼ 100 emu/cm3 for x>1.35. On the other hand, Ms remains unchanged with x increasing from 0.3 to 1 for the film grown on STO. With x>1, Ms drops abruptly to ∼ 100 emu/cm3, which is comparable to Ms of the film grown on MgO. The discrepancy in Ms of Fe3−xMgxO4 film grown on MgO and STO may imply that the cation distribution of these films may be fundamentally different. Possible cation distribution and the substrate strain effect will be discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
52.77.-j Plasma applications
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Dm X-ray absorption spectra
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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