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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Magnetic phase diagram of CuB2O4

M. Fiebig, I. Sänger, and R. V. Pisarev

J. Appl. Phys. 93, 6960 (2003); http://dx.doi.org/10.1063/1.1556159 (3 pages)

Online Publication Date: 9 May 2003

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The magnetic structure of CuB2O4 is investigated by optical second harmonic generation. A rich second harmonic spectrum is observed and at least three different magnetic phases in the magnetic-field/temperature plane are revealed for magnetic fields applied along the principal axes of the compound. In the temperature ranges T<TR and TR<T<TN (with TR=10 K and TN=21 K) antiferromagnetic phases without and with a weak spontaneous ferromagnetic component are observed, respectively. A static magnetic field supports the phase directly below TN and finally suppresses the magnetic reorientation at TR. © 2003 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Study of magnetic susceptibility of magnetite nanoparticles

A. F. R. Rodriguez, A. C. Oliveira, P. C. Morais, D. Rabelo, and E. C. D. Lima

J. Appl. Phys. 93, 6963 (2003); http://dx.doi.org/10.1063/1.1556160 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2003

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In this study dynamic susceptibility (DS) was used to investigate magnetite nanoparticles dispersed in styrene-divinylbenzene copolymer. Transmission electron microscopy (TEM) data have been used to support the DS data analysis. The field dependence of the peak position of the imaginary component of DS was analyzed using a picture of an asymmetric double well potential for the relaxation of the magnetic moment associated with the magnetite nanoparticle. The size dependence of the magnetic susceptibility was included in the data analysis. Nanoparticle-size parameters obtained from the analysis of the DS data (19.1 and 18.2 nm) are in excellent agreement with the values obtained from the fitting of the TEM data (19.2 and 20.1 nm). © 2003 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy

Drastic changes of the domain size in an ultrathin magnetic film

M. Kisielewski, A. Maziewski, V. Zablotskii, T. Polyakova, J. M. Garcia, A. Wawro, and L. T. Baczewski

J. Appl. Phys. 93, 6966 (2003); http://dx.doi.org/10.1063/1.1556161 (3 pages) | Cited 14 times

Online Publication Date: 9 May 2003

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A general framework for the domain size in any ultrathin film with perpendicular magnetic anisotropy is here discussed. The domain structure is analyzed by using the classical theory taking into consideration the demagnetization field contribution to the domain wall energy. A sinusoidal model is considered to describe the domain structure while approaching, in two different cases, the monodomain state with in-plane magnetization. The first case is realized applying a large enough in-plane magnetic field. The second one is obtained by decreasing the perpendicular magnetic anisotropy, which is connected in many ultrathin systems with the increase of film thickness. A change in the domain size of several orders of magnitude is obtained while approaching the magnetization reorientation region. The minimal stripe domain period p=8πlex2/d is calculated from the sinusoidal model, where lex is the exchange length and d is the thickness of the film. The range of possible domain size changes in ultrathin films is predicted. The domain size has been experimentally studied in a 1 nm Co film characterized by a square hysteresis loop. The investigations have been performed by polar Kerr based microscopy and magnetic force microscopy. The domain structure of two remnant states generated by applying an in-plane and a perpendicular magnetic field has been compared. Drastically, the smallest domain size has been observed for the former. © 2003 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Structure and magnetic properties of NiFe/SiO2 and Co/SiO2 nanocomposites consolidated by detonation compaction

Y. D. Zhang, X. Q. Ma, S. Hui, Mingzhong Wu, S. H. Ge, W. A. Hines, J. I. Budnick, B. M. Cetegen, and S. Y. Semenov

J. Appl. Phys. 93, 6969 (2003); http://dx.doi.org/10.1063/1.1558606 (3 pages)

Online Publication Date: 9 May 2003

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In this article, the structural and magnetic properties of NiFe/SiO2 and Co/SiO2 nanocomposites fabricated via powder processing are presented. The NiFe/SiO2 and Co/SiO2 nanoparticles were both synthesized by a wet chemistry approach. The as-synthesized nanoparticles were characterized by scanning electron microscopy, x-ray diffraction, and superconducting quantum interference device magnetometer, yielding detailed information concerning the structure and size of NiFe or Co particles, coating, and composition purification. The nanoparticles were then consolidated into solid components via detonation compaction. Depending on the powder morphology and detonation conditions, the density of the consolidated sample can reach over 91% of the theoretical density of the conventional materials. X-ray diffraction experiments on the samples both before and after consolidation indicate that the crystal structure of the nanocomposites remains unchanged during detonation consolidations; however, a rather large increase in particle size for the magnetic constituent was observed. Static magnetic property studies carried out on the samples both before and after detonation showed no change in the saturation magnetization after consolidation, indicating that the detonation consolidation does not cause oxidation of the nanopowders. Initial complex permeability measurements on the consolidated samples showed an essentially flat μ′ versus frequency response over a wide frequency range between 5 kHz and 13 MHz, implying a high resistivity of the consolidated sample. These experiments show that detonation compaction is a promising approach for consolidating magnetic nanoparticles, and NiFe/SiO2 and Co/SiO2 are good candidates for high frequency soft magnetic materials. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Noncollinearity of the magnetic structure of TbFe10V2

J. M. Cadogan, D. H. Ryan, O. Moze, I. P. Swainson, and K. Suzuki

J. Appl. Phys. 93, 6972 (2003); http://dx.doi.org/10.1063/1.1556162 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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We have studied the ThMn12-type compound TbFe10V2 by magnetometry and high-resolution neutron powder diffraction. Previous workers claimed that TbFe10V2 undergoes a spin reorientation away from the tetragonal c axis at around 200 K, with the collinear magnetization eventually reaching an angle of 50° at 4 K. We have reinvestigated TbFe10V2 due to the unusual temperature dependence of its magnetization. We show that this behavior cannot be explained by a compensation effect and we suggest that a canted, noncollinear magnetic structure develops below the spin-reorientation temperature. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Bb Fe and its alloys
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic, magneto-optical, and transport properties of ferromagnetic shape-memory Ni2MnGa alloy

S. J. Lee, Y. P. Lee, Y. H. Hyun, and Y. V. Kudryavtsev

J. Appl. Phys. 93, 6975 (2003); http://dx.doi.org/10.1063/1.1558607 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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The magnetic, transport, and magneto-optical properties of Ni2MnGa alloy in the martensitic and austenitic states were investigated. The temperature dependence of resistivity shows kinks at the structural and ferroparamagnetic transitions. The temperature dependence of magnetization was also investigated for both the bulk and the film. It was shown that the lack of crystallinity in the amorphous Ni2MnGa alloy films leads to the loss of ferromagnetic order above 4 K. The nature of the interband absorption peaks in the optical-conductivity spectra and in the absorptive part of off-diagonal components of the dielectric function for the authentic state of Ni2MnGa alloy was elucidated. © 2003 American Institute of Physics.
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81.30.Kf Martensitic transformations
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
78.20.Ls Magneto-optical effects
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Magnetic properties of Fe-doped organic–inorganic nanohybrids

N. J. O. Silva, V. S. Amaral, L. D. Carlos, and V. de Zea Bermudez

J. Appl. Phys. 93, 6978 (2003); http://dx.doi.org/10.1063/1.1556163 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2003

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We present a magnetic study of Fe-doped diureasils (siloxane-based networks to which poly(ethylene oxide)-based chains are grafted by urea cross linkages doped with Fe(II) or Fe(III) ions. Structural studies show that the Fe(II) ions interact mainly with the organic chain, whereas the incorporation of Fe(III) leads to the formation of iron-based nanoclusters, with radius increasing from 20 to 40 Å. Fe(II)-doped samples behave as simple paramagnets, with μeff=5.32 μB. Fe(III)-doped hybrids present antiferromagnetic interactions, with TN increasing with Fe(III) concentration up to 13.6 K for 6% doping. Thermal irreversibility was observed below ∼40 K and is stronger for higher concentrations. The coercive fields (HC) are of the order of 1000 Oe at 5 K. Hysteresis cycles are shifted to negative fields, revealing the presence of exchange anisotropy interactions with exchange fields (HE) of the order of 100 Oe. Both fields decrease rapidly with increasing temperature. We analyze this behavior in terms of the contribution of surface spin disorder to exchange anisotropy. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.70.Rf Surface magnetism
75.50.Ee Antiferromagnetics
81.07.Pr Organic-inorganic hybrid nanostructures
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)
81.05.Qk Reinforced polymers and polymer-based composites
75.20.Ck Nonmetals

Effects of carbon on magnetic properties and magnetic entropy change of the LaFe11.5Si1.5 compound

Yuan-fu Chen, Fang Wang, Bao-gen Shen, Ji-rong Sun, Guang-jun Wang, Feng-xia Hu, Zhao-hua Cheng, and Tao Zhu

J. Appl. Phys. 93, 6981 (2003); http://dx.doi.org/10.1063/1.1558658 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2003

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Effects of the interstitial carbon atoms on the magnetic properties, especially on the magnetic entropy change, of the LaFe11.5Si1.5 compound, have been studied. X-ray diffraction patterns reveal a monotonous increase of the lattice constant with the concentration of carbon, while the cubic NaZn13-type structure remains unchanged. The Curie temperatures TC of LaFe11.5Si1.5Cy are ∼195, 225, and 241 K for y=0, 0.2, and 0.5, respectively, increasing with the increase of carbon concentration. The maximal magnetic entropy changes ∣ΔS∣ of LaFe11.5Si1.5Cy at the respective TC under a magnetic field change of 0–5 T are ∼24.6, ∼22.8, and ∼12.7 J/kg K for y=0, 0.2, and 0.5, respectively, notably exceeding that of Gd (∣ΔS∣ ∼9.8 J/kg K at TC=293 K). The ∣ΔS∣ of LaFe11.5Si1.5C0.2 is nearly as giant as that of the parent alloy LaFe11.5Si1.5 due to the first-order field-induced itinerant-electron metamagnetic transition that occurs in both compounds clearly observed for the LaFe11.5Si1.5C0.5 compound. With the increase of carbon concentration, the nature of magnetic transition has been changed from first order to second order, which results in the significant decrease of the magnetic entropy change. The large ∣ΔS∣, convenient adjustment of TC and relatively low cost make the LaFe11.5Si1.5Cy interstitial compounds promising candidates for magnetic refrigerants in the corresponding temperature range. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Dk Alloys
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
61.72.J- Point defects and defect clusters

Multiple magnetic transitions and magnetoresistance anomalies in the Er0.9Tb0.1Mn6Sn6 compound

Jin-lei Yao, Shao-ying Zang, Lu Li, Tao Zhu, Mi Yan, De-ren Yang, and Bao-gen Shen

J. Appl. Phys. 93, 6984 (2003); http://dx.doi.org/10.1063/1.1556164 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The magnetic and transport properties of the Er0.9Tb0.1Mn6Sn6 compound have been investigated in the temperature range of 5–375 K. The compound shows paramagnetism, ferrimagnetism, antiferromagnetism, and reentrant ferrimagnetism with decreasing temperature. Around 60 K, a spin orientation takes place, the easy magnetization direction changing from the c axis to the ab plane. The antiferroferrimagnetic transition is accompanied by a large magnetoresistance (MR) effect of about −5.5% at 200 K in a magnetic field of 50 kOe. It is observed that the sign of MR reverses to positive below 25 K. © 2003 American Institute of Physics.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.47.Np Metals and alloys
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.20.En Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Enhancement of Curie temperature in double perovskites Ba2−xLaxFeMoO6

H. M. Yang, W. Y. Lee, H. Han, B. W. Lee, and C. S. Kim

J. Appl. Phys. 93, 6987 (2003); http://dx.doi.org/10.1063/1.1556253 (3 pages) | Cited 14 times

Online Publication Date: 9 May 2003

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We have investigated effects of the partial substitution of trivalent La for divalent Ba on the magnetic properties of the double perovskite Ba2FeMoO6. Polycrystalline Ba2−xLaxFeMoO6 samples have been prepared by the conventional solid-state reaction in a stream of 5% H2/Ar gas. Magnetization (15 K, 5 kOe) is 2.6μB/f.u. for x=0.5 which is smaller than the value of 3.8μB/f.u. for x=0. The partial substitution of La3+ for Ba2+ considerably enhances the Curie temperature TC. The TC increases from 316 K for x=0 to 336 K for x=0.5. © 2003 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Ferromagnetic and ferroelectric behaviors of A-site substituted YMnO3-based epitaxial thin films

N. Fujimura, H. Sakata, D. Ito, T. Yoshimura, T. Yokota, and T. Ito

J. Appl. Phys. 93, 6990 (2003); http://dx.doi.org/10.1063/1.1556165 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2003

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Dielectric and magnetic properties of A-site substituted YMnO3 epitaxial films were studied. Stoichiometric epitaxial YMnO3 films clearly show ferroelectric behavior in P–E and C–V measurements. The I–V property is well explained by the Pool–Frenkel-type carrier emission with p-type conduction due to the existence of Mn4+, and the activation energy is calculated to be 0.58 eV. The leakage current decreases by substituting Y for Zr and increases by Li or Mg substitution. Although YMnO3 films exhibit antiferromagnetic magnetization behavior regardless of the crystallographic orientation and the carrier concentration, Li-doped sample displays parasitic ferromagnetic behavior (weak ferromagnetism). Substituting Y for Yb enhances the ferromagnetic interaction. © 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.Dd Nonmetallic ferromagnetic materials
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.50.Fq High-field and nonlinear effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
73.61.Le Other inorganic semiconductors

Magnetic properties of highly resistive BaFeO3 thin films epitaxially grown on SrTiO3 single-crystal substrates

T. Matsui, E. Taketani, N. Fujimura, T. Ito, and K. Morii

J. Appl. Phys. 93, 6993 (2003); http://dx.doi.org/10.1063/1.1556166 (3 pages) | Cited 15 times

Online Publication Date: 9 May 2003

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We have synthesized single-crystalline films of BaFeO3 (BFO), which may contain unusual tetravalent Fe ions, on (100) and (111) SrTiO3 substrates by pulsed laser-beam deposition. The epitaxially grown BFO is considered to have a pseudocubic perovskite-type crystal structure with some oxygen vacancies. The films were found to be highly insulating, and showed a high value of dielectric constant of ϵ=59. The magnetization curve of the films exhibited hysteresis, as well as small remanent magnetization. The origin of the observed small magnetization can be ascribed to the mixed valence state of the Fe4+ and Fe3+ ions. The present epitaxially grown BFO apparently had some different magnetic and dielectric properties from those for bulk BFO as well as for the previously reported other Fe4+ oxides: coexisting high resistivity and spontaneous magnetization at room temperature. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
77.22.Ch Permittivity (dielectric function)
61.72.J- Point defects and defect clusters
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds

Magnetic and neutron diffraction study on Ni2In type (Mn1−xPdx)2Ga

Hiroshi Shiraishi, Tomiei Hori, Naoki Ohkubo, Kenji Ohoyama, and Yasuo Yamaguchi

J. Appl. Phys. 93, 6996 (2003); http://dx.doi.org/10.1063/1.1556254 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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Pseudobinary intermetallic compounds (Mn1−xPdx)2Ga of Ni2In type structure are found in the range of 0.3≦x<0.6. This article describes the results of investigations of the crystal and magnetic properties of the phase with x-ray and neutron diffraction, as well as magneto metric methods. The neutron diffraction study for x=0.4 proved that in the Ni2In type crystal structure, the 2(a) site is occupied by Mn atoms, the 2(d) site by Pd and residual Mn atoms, and the 2(c) site is occupied by Ga atoms. (Mn1−xPdx)2Ga compounds exhibit a ferromagnetic nature characterized by TC, and in the temperature below TN, antiferromagnetic components originating from canted spin structure in 2(a) structures in the 2(a) site. It is similar to canted spin structures of CoMnSn. The existence of a small concave region in the magnetization–temperature dependence curve is discussed in terms of the canting of spins in the 2(a) site. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
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