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15 May 2002

Volume 91, Issue 10, pp. 6227-8917

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Synthesis of nanosized (Li0.5xFe0.5xZn1−x)Fe2O4 particles and magnetic properties

S. H. Gee, Y. K. Hong, M. H. Park, D. W. Erickson, P. J. Lamb, and J. C. Sur

J. Appl. Phys. 91, 7586 (2002); http://dx.doi.org/10.1063/1.1453931 (3 pages) | Cited 4 times

Online Publication Date: 13 May 2002

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In an attempt to synthesize nanosized (Li0.5xFe0.5xZn1−x)Fe2O4 (0⩽x⩽1) particles with high magnetic saturation and low coercivity, the energetic ball milling technique was employed. LiCO3, α-Fe2O3, and ZnO powders were used as starting materials. The ball milled, partially crystallized lithium zinc ferrite starts to crystallize at about 600 °C. This is much lower than the temperature of 1000 °C, which is used in conventional methods. Particle size of lithium zinc ferrite was in the range of 20 to 50 nm. Regardless of the annealing temperature, the saturation magnetization increases with increasing x and reaches the maximum (about 80 emu/g) at x=0.7 [(Li0.35Fe0.35Zn0.3)Fe2O4], followed by a decrease to 60 emu/g for x=1 [(Li0.5Fe0.5)Fe2O4]. On the other hand, the coercivity of x=0.7 composition decreases with increasing annealing temperatures. Saturation magnetization and low coercivity for x=0.7 annealed at various temperatures are discussed in terms of site occupation. © 2002 American Institute of Physics.
Show PACS
81.07.Bc Nanocrystalline materials
81.07.Wx Nanopowders
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Synthesis of ferrite and nickel ferrite nanoparticles using radio-frequency thermal plasma torch

S. Son, M. Taheri, E. Carpenter, V. G. Harris, and M. E. McHenry

J. Appl. Phys. 91, 7589 (2002); http://dx.doi.org/10.1063/1.1452705 (3 pages) | Cited 51 times

Online Publication Date: 13 May 2002

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Nanocrystalline (NC) ferrite powders have been synthesized using a 50 kW–3 MHz rf thermal plasma torch for high-frequency soft magnet applications. A mixed powder of Ni and Fe (Ni:Fe=1:2), a NiFe permalloy powder with additional Fe powder (Ni:Fe=1:2), and a NiFe permalloy powder (Ni:Fe=1:1) were used as precursors for synthesis. Airflow into the reactor chamber was the source of oxygen for oxide formation. XRD patterns clearly show that the precursor powders were transformed into NC ferrite particles with an average particle size of 20–30 nm. SEM and TEM studies indicated that NC ferrite particles had well-defined polygonal growth forms with some exhibiting (111) faceting and many with truncated octahedral and truncated cubic shapes. The Ni content in the ferrite particles was observed to increase in going from mixed Ni and Fe to mixed permalloy and iron and finally to only permalloy starting precursor. The plasma-torch synthesized ferrite materials using exclusively the NiFe permalloy precursor had 40%–48% Ni content in the Ni-ferrite particle, differing from the NiFe2O4 ideal stoichiometry. EXAFS was used to probe the cation coordination in low Ni magnetite species. The coercivity and Neel temperature of the high Ni content ferrite sample were 58 Oe and ∼590 °C, respectively. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
52.77.-j Plasma applications
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Anomalous variation of coercivity with annealing in nanocrystalline NiZn ferrite films

Mrugesh Desai, Shiva Prasad, N. Venkataramani, Indradev Samajdar, A. K. Nigam, N. Keller, R. Krishnan, E. M. Baggio-Saitovitch, B. R. Pujada, and A. Rossi

J. Appl. Phys. 91, 7592 (2002); http://dx.doi.org/10.1063/1.1447504 (3 pages) | Cited 16 times

Online Publication Date: 13 May 2002

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The sputter deposited NiZn ferrite thin films were studied as a function of annealing temperature. The magnetization showed a monotonic increase with increasing annealing temperature. The coercivity shows a minimum at annealing temperature of 400 °C and shows a value of 14 Oe. Transmission electron microscopy study indicated that the grain size increases from ∼3 nm for the as-deposited case to ∼15 nm for the film annealed at 800 °C. The observed coercivity behavior could be attributed to the defects present in the films, the change in cation distribution, and the grain growth. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
61.72.Cc Kinetics of defect formation and annealing

Magnetism and structure of ZnxFe3−xO4 films processed via spin-spray deposition

Mitra Taheri, E. E. Carpenter, V. Cestone, M. M. Miller, M. P. Raphael, M. E. McHenry, and V. G. Harris

J. Appl. Phys. 91, 7595 (2002); http://dx.doi.org/10.1063/1.1456428 (3 pages) | Cited 12 times

Online Publication Date: 13 May 2002

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Zn-ferrite films, ZnxFe3−xO4 where the Zn:Fe ratio ranges from 0.36 to 0.76, were grown on glass substrates using a spin spray technique. Films are shown using scanning electron microscopy and atomic force microscopy to be dense and granular with an average grain size ∼0.3 μm. X-ray diffraction indicates that the films are a Fd3m symmetry consistent with a pure spinel ferrite phase. The films’ coercive fields have a strong positive correlation with the film roughness indicating the dominance of a physical domain wall pinning mechanism. The films are smooth and magnetically soft near the ZnFe2O4 stoichiometry. All films, including those near the ZnFe2O4 stoichiometry, display ferrimagnetic behavior with compensation temperatures well above the bulk Neel temperature of 9.5 K; this is attributed to the cation disorder measured in the Zn cation distribution. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
81.15.Rs Spray coating techniques
68.55.-a Thin film structure and morphology
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Photoinduced magnetic effects in bulk single-crystalline, polycrystalline, and LPE films of Yttrium Iron Garnet

K. Hisatake, I. Matsubara, K. Maeda, T. Fujiwara, M. Peters, S. Abe, K. Kudo, S. Kainuma, T. Tamaki, Y. Kino, C. de Francisco, J. M. Munoz, O. Alejos, P. Hernandez, C. Torres, et al.

J. Appl. Phys. 91, 7598 (2002); http://dx.doi.org/10.1063/1.1449439 (3 pages)

Online Publication Date: 13 May 2002

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The effect of light on magnetic initial permeability (the so-called photomagnetic effect) and photoinduced disaccommodation were studied in samples of yttrium iron garnet over the temperature range 77–300 K. The samples studied were bulk crystalline, produced by the floating zone method and the flux method, polycrystalline, produced by the usual sintering method, and single-crystalline films, produced by in situ liquid-phase epitaxis. One or both of the studied phenomena were observed in our experimental samples. To explain the experimental results, we suggest there is photoinduced structural distortion around oxygen vacancies due to a photoinduced change of charge imbalance. © 2002 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.70.Ak Magnetic properties of monolayers and thin films
61.72.J- Point defects and defect clusters
75.60.Lr Magnetic aftereffects

Sum rules on the dynamic permeability of hexagonal ferrites

A. L. Adenot, O. Acher, T. Taffary, and L. Longuet

J. Appl. Phys. 91, 7601 (2002); http://dx.doi.org/10.1063/1.1447505 (3 pages) | Cited 14 times

Online Publication Date: 13 May 2002

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A general sum rule has been established recently, bounding the integral of the gyromagnetic losses weighted by the frequency, by the square of the saturation magnetization [O. Acher and A. L. Adenot, Phys. Rev. B 62, 11324 (2000)]. This rule has been established for soft materials with internal anisotropy fields small compared to Bs. In this article, this result is extended to the case of hexagonal ferrites with strong planar anisotropy. It is shown that the bound on the integral is a simple expression of the saturation magnetization and of the out-of-plane anisotropy field. Experimental results on polycrystalline (Ba3Co2Fe24O41)-Co2Z and (BaCo1.25Ti1.25Fe9.5O19)-M hexagonal ferrites are presented. It is shown that the dynamic properties measured up to 18 GHz are bounded in agreement with our predictions. © 2002 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy

Ferromagnetic resonance of Fe–Sm–O thin films

Jong-Sung Baek, Seong-Gi Min, Seong-Cho Yu, and Woo-Young Lim

J. Appl. Phys. 91, 7604 (2002); http://dx.doi.org/10.1063/1.1452213 (3 pages)

Online Publication Date: 13 May 2002

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In order to investigate the temperature and the annealing conditions dependence of magnetic properties in Fe72.1Sm5.2O22.7(at. %) thin films, such as the effective magnetization Meff, the spectroscopic splitting factor g, and the exchange stiffness constant A, we carried out ferromagnetic resonance (FMR) experiments. Fe–Sm–O thin films were deposited in an argon and oxygen mixed atmosphere using a rf magnetron sputtering apparatus at room temperature. The g is almost constant in the temperature range from 298 to 238 K, but increases with decreasing temperature in the range below 238 K. The A increases slightly with decreasing temperature to 238 K, and then increases linearly below 238 K. When the annealing time increases up to 6 h the Meff is almost constant, but the A decreases slightly with increasing annealing time. © 2002 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
61.72.Cc Kinetics of defect formation and annealing
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Magnetic and structural properties of ultrafine CoFe1.9RE0.1O4 (RE=Gd, Nd) powders grown by using a sol-gel method

Woo Chul Kim, Sam Jin Kim, and Chul Sung Kim

J. Appl. Phys. 91, 7607 (2002); http://dx.doi.org/10.1063/1.1452214 (3 pages) | Cited 1 time

Online Publication Date: 13 May 2002

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Ultrafine CoFe1.9RE0.1O4 (RE=Gd, Nd) powders have been fabricated by a sol-gel method. Magnetic and structural properties of the powders were investigated by x-ray diffractometer, Mössbauer spectroscopy, and vibrating sample magnetometer. The CoFe1.9Gd0.1O4 powders that were fired at and above 923 K contained only a single spinel phase and behaved ferrimagnetically. The grain diameters were estimated to be 11–30 nm for the Co-Gd ferrite powders fired in 773–1123 K. Mössbauer spectra measurements showed that the CoFe1.9Gd0.1O4 powders fired at 723–823 K and the CoFe1.9Nd0.1O4 powders fired at 523–1023 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. Mössbauer spectra of the Co–Gd ferrite powder fired at 923 K were taken at various temperatures ranging from 14 to 875 K. The iron ions at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Néel temperature TN was found to be 875±2 K. Debye temperatures for A and B sites were found to be ΘA=640±5 K and ΘB=217±5 K, respectively. The magnetic behaviors of the CoFe1.9Gd0.1O4 powders fired at and above 723 K, and CoFe1.9Nd0.1O4 powders fired at and above 923 K, respectively, showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum coercivity and the saturation magnetization were Hc=1,149 Oe and Ms=72 emu/g in the CoFe1.9Gd0.1O4 samples and Hc=959 Oe and Ms=63 emu/g in the CoFe1.9Nd0.1O4 samples. © 2002 American Institute of Physics.
Show PACS
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.50.Vv High coercivity materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ww Permanent magnets
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Magnetic properties of Zn2+ substituted ultrafine Co-ferrite grown by a sol-gel method

Seung Wha Lee, Yeon Guk Ryu, Kea Joon Yang, Kwang-Deog Jung, Sung Yong An, and Chul Sung Kim

J. Appl. Phys. 91, 7610 (2002); http://dx.doi.org/10.1063/1.1452215 (3 pages) | Cited 3 times

Online Publication Date: 13 May 2002

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Ultrafine Co1−xZnxFe2O4 (0⩽x⩽1.0) particles are fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with x-ray diffraction, vibrating samples magnetometer and Mössbauer spectroscopy. The lattice parameter (a0) increases linearly with increasing Zn concentration (x) and follows Vegard’s law approximately. Co0.9Zn0.1Fe2O4 powders that were annealed at and above 673 K have only a single phase spinel structure and behave ferrimagnetically. Powders annealed at 523 K and 573 K have a typical spinel structure and are simultaneously paramagnetic and ferrimagnetic in nature. The magnetic behavior of Co0.9Zn0.1Fe2O4 powders annealed at and above 573 K shows that an increase of the annealing temperature yields a decrease of the coercivity and an increase of the saturation magnetization. The maximum coercivity and the saturation magnetization of Co0.9Zn0.1Fe2O4 ferrite powders are 1328 Oe and 81.1 emu/g, respectively. Mössbauer spectra of Co–Zn ferrite have been taken at various temperatures from 20 to 800 K. The isomer shifts indicate that the iron ions were ferric at the tetrahedral [A] and the octahedral [B]. The Néel temperature of Co0.9Zn0.1Fe2O4 was determined to be TN=790 K and It is found that Debye temperature for the A and B sites of the sample annealed at 1123 K is found to be ΘA=756±5 K and ΘB=199±5 K, respectively. The Néel temperature dramatically decreased with increasing x from about TN=870 K for x=0.0 to TN=35 K for x=1.0. © 2002 American Institute of Physics.
Show PACS
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Z type Ba hexagonal ferrites with tailored microwave properties

P. Lubitz and F. J. Rachford

J. Appl. Phys. 91, 7613 (2002); http://dx.doi.org/10.1063/1.1453932 (3 pages) | Cited 12 times

Online Publication Date: 13 May 2002

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The microwave properties of Z type Ba hexagonal ferrites with uniaxial anisotropy can be controlled over a wide range by choice of an appropriate mixture of Zn, Ni, and Co as divalent species. Using unmagnetized powders of these ferrites, the microwave permeability spectra were taken in a swept frequency mode in the temperature range 200–550 K. From these data, the product γHa was derived. SQUID magnetometry was used to measure the magnetization and anisotropy separately. Pure Zn or Co Z type ferrites were found to have temperature dependences of γHa similar to those of other hexagonal ferrites containing Zn or Co, i.e., nearly flat for Zn and strongly increasing with T for Co. Ni–Z ferrite is notably different: the combination γHa, which determines the frequency of maximum absorption, is found to decrease rapidly with increasing temperature near 300 K. Magnetometry indicates that this temperature dependence γHa is caused mostly by variation of Ha with temperature. The temperature dependence of γHa for Ni–Z suggests a strategy to compensate the strong and opposing temperature dependence of γHa induced by Co ions, which are used to reduce Ha. By independently varying the mix of Zn, Co, and Ni in these ferrites, a useful range of microwave resonance frequencies, γHa, were obtained without undesirable temperature dependence near 300 K. This strategy may allow use of these materials as self-biased microwave components or for absorbing microwave energy in the 5–20 GHz range.
Show PACS
75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.40.-x Radiowave and microwave (including millimeter wave) technology

Oriented Y-type hexaferrites for ferrite device

M. Obol, X. Zuo, and C. Vittoria

J. Appl. Phys. 91, 7616 (2002); http://dx.doi.org/10.1063/1.1446113 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2002

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We have developed a technique to orient particles of Y-type hexaferrite in which the c axis of the particles is oriented perpendicular to a plane. Disks of oriented Ba2MnZnFe12O22 particles were characterized in static and dynamic field excitations and exhibited the following properties: 4πMs=2300 G, Ha=9500 G, 4πMeff=4πMs+Ha=11800 G, and Hc=60 Oe. The ferrimagnetic resonance linewidth at 27 GHz measured to be 350 Oe and the g factor approximately equal to 2. The magnetic parameters of the oriented particles were very similar to the bulk parameters previously published. © 2002 American Institute of Physics.
Show PACS
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy

Effects of grain size on the residual loss of Mn–Zn ferrites

Weon Hee Jeong, Young Ho Han, and Byung Moo Song

J. Appl. Phys. 91, 7619 (2002); http://dx.doi.org/10.1063/1.1447506 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2002

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The effect of grain sizes on the electromagnetic properties of Mn–Zn ferrites has been studied up to MHz range. The average grain sizes ranging between 2 and 5 μm were obtained by varying the sintering time from 2 to 12 h. The total power loss at 1 MHz, 25 mT, and 100 °C increased with grain size. The hysteresis loss decreased with increasing grain size, while the eddy current loss and the residual loss increased. The residual loss showed a drastic increase at the grain size around 4 μm, which confirms that the residual loss due to the domain wall resonance should be taken into account at a grain size greater than the monodomain dimension. © 2002 American Institute of Physics.
Show PACS
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.60.Ch Domain walls and domain structure
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
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