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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Mn–Zn spinel ferrite thin films prepared by high rate reactive facing targets sputtering

Shigeki Nakagawa, Shunsuke Saito, Taro Kamiki, and Sok-Hyun Kong

J. Appl. Phys. 93, 7996 (2003); http://dx.doi.org/10.1063/1.1555842 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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Mn–Zn ferrite thin films were deposited by sputtering a Mn0.6Zn0.4Fe2 alloy target, which was fabricated by powder metallurgy, in a mixture gas of Ar and O2. A 12 nm thick Pt underlayer was deposited at a substrate temperature of 300 °C. All specimen films were prepared in a reactive facing targets sputtering system. The degree of oxidization of the film is strongly related to the oxidation condition at the surface of the target. The surface condition of the target can be estimated by monitoring the discharge voltage. The discharge current–voltage characteristics clarify that there are three regions for the surface condition of the target, i.e. “oxidized,” “metallic,” and “transition.” Mn–Zn ferrite films with (111) crystallite orientation were deposited on Pt(111) underlayer under the transition region condition. The film prepared at O2 partial pressure ratio of 25% revealed 4.8 kG of saturation magnetization 4πMs. The deposition rate of the reactive sputtering method is 16 times as high as that of the conventional method. © 2003 American Institute of Physics.
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75.50.Gg Ferrimagnetics
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
81.65.Mq Oxidation

Growth and characterization of BSTO/hexaferrite composite thin films

R. Hajndl, J. Sanders, H. Srikanth, and N. J. Dudney

J. Appl. Phys. 93, 7999 (2003); http://dx.doi.org/10.1063/1.1543129 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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Ferroelectric/ferrite composite films are excellent systems in which the electromagnetic material properties can be tuned through changes in composition as well as microstructure. We report on our studies of the structural and magnetic properties of Ba0.5Sr0.5TiO3/BaFe12O19 (BSTO/BaM) composite thin films deposited on Al2O3 substrates using magnetron sputtering. Optimizing the sputtering conditions and postdeposition annealing lead to high-quality films without any impurity phases. Magnetic measurements yield saturation magnetization values in the range of 100 to 200 emu/cm3. Hysteresis loops exhibit a double transition that is observed only in the composite films and not in pure hexaferrite films grown under identical deposition conditions. The unusual feature in the M–H data is ascribed to the possibility of magnetodielectric effects associated with intergranular magnetic coupling mediated by the BSTO polarization layer. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
77.55.-g Dielectric thin films
75.50.Gg Ferrimagnetics
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Effect of radio-frequency noise suppression on the coplanar transmission line using soft magnetic thin films

Ki Hyeon Kim, Masahiro Yamaguchi, Ken-Ichi Arai, Hideaki Nagura, and Shigehiro Ohnuma

J. Appl. Phys. 93, 8002 (2003); http://dx.doi.org/10.1063/1.1558084 (3 pages) | Cited 34 times

Online Publication Date: 9 May 2003

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We demonstrated the radio-frequency (rf) noise suppressor using soft magnetic films on a coplanar transmission line from 0.1 to 20 GHz. The coplanar transmission line is composed of magnetic film/polyimide/Cu transmission line/seed layer (Cu/Ti)/glass substrate with the dimension of 50 μm width of the signal line and 3 μm thickness (characteristic impedance: 50 Ω). The magnetic films (CoPdAlO, CoZrO, and CoNbZr) as a noise suppressor are prepared by rf sputtering. The saturation magnetization of each magnetic film is about 10 kG. The magnetic anisotropy field and the ferromagnetic resonance frequency are 230, 89, and 6 Oe and 4.2, 2.5, and 0.7 GHz, respectively. The power loss of the coplanar line with magnetic films is significantly larger than without magnetic and nonmagnetic films due to ferromagnetic resonance losses. © 2003 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Magnetic and magneto-optical properties of neodymium gallium garnet under “extreme” conditions

Maurice Guillot, Xing Wei, Donovan Hall, You Xu, Jie Hui Yang, and Fang Zhang

J. Appl. Phys. 93, 8005 (2003); http://dx.doi.org/10.1063/1.1558086 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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The magnetization and Faraday rotation (FR) of Nd3 Ga5 O12 (NdGaG) were studied under high magnetic fields up to 33 T and low temperatures down to 4.2 K. No saturation of the magnetization was observed. The magnetic moment of the fundamental doublet was determined to be close to 1.25 μB/ion, with the energy gap with respect to the nearest level of about 132 cm−1. Above 30 K, the magnetic moment, M(H), shows a linear field dependence, even at the maximum field. The reciprocal magnetic susceptibility follows the Curie–Weiss law at temperatures above 100 K, with a Curie constant of about 15% below that of free ions. At 4.2 K, the FR spectrum is strongly field dependent, with very strong signals in the wavelength range from 440 to 720 nm. The FR signal decreases rapidly with increasing wavelengths above 720 nm and retains very small values in the wavelength range from 800 to 850 nm. The results are briefly discussed in light of a recent theoretical analysis of the magnetic and FR properties of the isomorphous ferrimagnetic garnet (Nd:YIG). © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities

Field-induced phase transitions in Sc-substituted ytterbium–iron–garnet under high dc fields

J. Ostoréro and M. Guillot

J. Appl. Phys. 93, 8008 (2003); http://dx.doi.org/10.1063/1.1558192 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2003

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High magnetic field measurements were performed on Yb3Fe5−xScxO12 (YbIG:Sc), x=0.5, single crystals platelets oriented along the [111] and [100] crystallographic axes, in the 4.2 K–250 K temperature range in a magnetic field up to 230 kOe. When T=4.2 K, a first-order transition is observed at 63 kOe for H applied parallel to [111]. For 4.2 K<T<25 K, an anisotropy of magnetization is observed below 70 kOe, the differential magnetic susceptibility presenting a maximum independent of temperature at H=125 kOe. In this temperature range, [111] is the “easy” magnetic axis in the spontaneous state. For T>25 K, isotherms are linear as usually observed in ferrites. However, isofield curves reveal the presence of a singular point at 60 K that indicates that the field-induced canted magnetic structures remain until this temperature. The magnetic phase diagram is then established. The spontaneous magnetization data are analyzed within the frame of the Dionne-refined Néel model. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Synthesis and characterization of Zn2U (Ba4Zn2Fe36O60) hexaferrite powder

D. Lisjak and M. Drofenik

J. Appl. Phys. 93, 8011 (2003); http://dx.doi.org/10.1063/1.1540159 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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Polycrystalline Zn2U (Ba4Zn2Fe36O60) was synthesized. The high-energy milling of the starting powders activated the synthesis of the Zn2U at 1100 °C. Energy dispersive spectroscopy supported by x-ray diffraction analysis confirmed that pure Zn2U was synthesized in the temperature range 1200–1300 °C. The magnetic properties of the Zn2U were measured. The coercivity varied with the synthesis conditions, while the saturation magnetization was independent of the synthesis conditions. Nevertheless, both the coercivity and the saturation magnetization were different from those of the basic components of the Zn2U crystal structure: M (BaFe12O19) and Zn2Y (Ba2Zn2Fe12O22).© 2003 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
81.20.Wk Machining, milling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Explosion compacted FeCo particles coated with ferrites: A possible route to achieve artificial soft ferrites

Y.-W. Zhao, Tao Zhang, and John Q. Xiao

J. Appl. Phys. 93, 8014 (2003); http://dx.doi.org/10.1063/1.1558088 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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A simple and effective method has been developed to coat soft ferromagnetic particles (e.g., FeCo alloy) with a thin (1–3 nm) CoFe2O4 or NiFe2O4 layer. A general tendency of coercivity enhancement after the ferrites coating has been observed, which we ascribe to the exchange coupling between the ferromagnetic core and the ferrimagnetic coating shell. Using explosion compaction technique, the ferrite-coated particles were compacted into fully dense bulk material with density very close to the ideal value. The impedance of the compacted sample was measured in the frequency range of 1 kHz–100 MHz. The real part of measured impedance for our compacted sample is very high and decreases with increasing frequency much slower than a standard ferrite sample in the range of 35 kHz–4.2 MHz. While the hysteresis loops at 5 K for free-standing ferrite-coated particles cooled under 5 T field show a few tens Oe shift in the negative field direction indicating a typical antiferromagnetic-like exchange coupling behavior, the compacted bulk materials give symmetrical hysteresis loops in both field or zero-field cooling. This may be understood in the context of exchange coupling in random anisotropic systems. Our results are promising for high frequency magnetic devices applications. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy

Calculation of exchange integrals and electronic structure of manganese ferrite (MnFe2O4)

Xu Zuo and Carmine Vittoria

J. Appl. Phys. 93, 8017 (2003); http://dx.doi.org/10.1063/1.1558200 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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The exchange integrals of manganese ferrite (MnFe2O4) are calculated with the density functional theory method for both normal and inverse spinel structures. The functional is chosen to be a mixture of Becke exchange and Fock exchange with variable weight (w). The exchange integrals JAB (the exchange integral between the nearest neighbor A and B sites) and JBB (the exchange integral between nearest neighbor B sites) are calculated by substituting the total energies of different magnetic ground states into the Heisenberg model. The calculated value of JAB is in agreement with experimental values measured by neutron diffraction and nuclear magnetic resonance. Also, the parameters U (Coulomb repulsion energy) and Eg (band gap) are extracted from density of states plotted versus w. Our calculated band gap shows that MnFe2O4 is a complex insulator in contrast to previous local spin density approximation and generalized gradient approximation calculations which predicted it to be metallic. © 2003 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.30.Et Exchange and superexchange interactions
71.20.Ps Other inorganic compounds
75.10.Lp Band and itinerant models
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.10.Jm Quantized spin models, including quantum spin frustration

Micromagnetic simulation of thermal ripple in thin films: “Roller-coaster” visualization

Xuebing Feng, P. B. Visscher, and D. M. Apalkov

J. Appl. Phys. 93, 8020 (2003); http://dx.doi.org/10.1063/1.1556094 (3 pages)

Online Publication Date: 9 May 2003

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We present simulations of pulse-induced magnetization-rotation experiments in Permalloy. These lead to temporary domain formation (“thermal ripple”) and help to explain the time dependence of experimental results. To understand and visualize the motion, we find it very useful to exploit a mathematical isomorphism of this problem (in the limit Ms≫Hpulse) to the problem of a massive particle on a circular track (“roller coaster”). The height (gravitational potential energy) of this track is proportional to the Stoner–Wohlfarth energy. The fact that the resulting “precession” is really oscillation in a plane, and the fact that this oscillation overshoots the minimum-energy configuration (the inertia effect) are much more intuitive in the roller coaster picture than in the conventional “M precesses about the effective field” picture. Animated simulations of this behavior are available on the web (http://bama.ua.edu/∼visscher/mumag/). © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
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