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15 May 2005

Volume 97, Issue 10, Articles (10xxxx)

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back to top Ferrites, Garnets, and Other Microwave Materials

Mössbauer spectroscopy investigation of Mn-substituted Co-ferrite (CoMnxFe2−xO4)

K. Krieble, T. Schaeffer, J. A. Paulsen, A. P. Ring, C. C. H. Lo, and J. E. Snyder

J. Appl. Phys. 97, 10F101 (2005); http://dx.doi.org/10.1063/1.1846271 (3 pages) | Cited 18 times

Online Publication Date: 10 May 2005

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Understanding the effect of Mn substitution for Fe in Co ferrite presents a challenge because there are three different transition-metal ions distributed among two distinct crystallographic and magnetic sublattices with complicated superexchange and anisotropic interactions. In this study, a series of six powder samples with compositions Co1.0MnxFe2−xO4 were investigated using transmission Mössbauer spectroscopy. Mössbauer spectroscopy provides an excellent tool for probing the local environment of the Fe atoms present in such materials. Results show two sets of six-line hyperfine patterns for all samples, indicating the presence of Fe in both A and B sites. Identification of sites is accomplished by evidence from hyperfine distribution width, integrated intensity, and isomer-shift data. Increasing Mn concentration was found to decrease the hyperfine field strength at both sites, but at unequal rates, and to increase the distribution width. This effect is due to the relative strengths of Fe–O–X superexchange (X = Fe, Co, or Mn) and the different numbers of the next-nearest neighbors of A and B sites. Results are consistent with a model of Mn substituting into B sites and displacing Co ions onto A sites.
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75.50.Gg Ferrimagnetics
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Order-disordered structure and magnetic properties of Li0.5Fe2.5−xRhxO4

Kun Uk Kang, Chul Sung Kim, and Hang Nam Oak

J. Appl. Phys. 97, 10F102 (2005); http://dx.doi.org/10.1063/1.1849553 (3 pages) | Cited 3 times

Online Publication Date: 10 May 2005

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Li0.5Fe2.5−xRhxO4 (x = 0.25–1.50) has been studied by Mössbauer spectroscopy, superconducting quantum interference device magnetometry, and x-ray diffraction. The crystals are found to be a cubic spinel structure and have been classified into two different sets by crystallographic symmetry, the space group Fd3m for x = 0.25–1.25 and the space group Fmath3m for x = 1.50, respectively. The migration of Li ion has been confirmed by x-ray patterns and the results of Mössbauer analysis. The saturated magnetic moment measured at 4.2 K and Mössbauer spectra taken at various temperatures with 6.0 T applied field show that the spin structure of Li0.5Fe2.5−xRhxO4 has the collinear Néel model.
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75.50.Gg Ferrimagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Mg Numerical simulation studies
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Simple derivation of four-level permittivity relations for magneto-optical applications

Gerald F. Dionne

J. Appl. Phys. 97, 10F103 (2005); http://dx.doi.org/10.1063/1.1849692 (3 pages) | Cited 4 times

Online Publication Date: 10 May 2005

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An analysis based on the gyromagnetic permeability tensor is applied to electric dipole transitions between orbital angular momentum terms of the four-level math↔math group that serves as the model for magneto-optical properties in the near-infrared region. The final expressions for the permittivity tensor elements are obtained by combining the line shape functions for the two pairs of resonance and nonresonance contributions of the respective circular polarization modes that are separated by the multiplet splitting of the math term. For a split ground state, the effect of temperature on population differences is introduced by a simple Boltzmann approximation. This approach affords complete flexibility in the selection of permittivity for all weightings of circular polarization. By direct algebraic summations, the combined permittivities can be readily computed for systems with various magneto-optical spectra. Signal loss effects can be introduced at any stage by substitution of the standard ferrimagnetic resonance damping models that characterize the resonance linewidth.
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78.20.Ls Magneto-optical effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Cr Saturation moments and magnetic susceptibilities
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Calculation of exchange constants in spinel ferrites with magnetic S-state ions

Xu Zuo, Yongxue He, Aria Yang, Barbiellini Bernardo, Vincent G. Harris, and Carmine Vittoria

J. Appl. Phys. 97, 10F104 (2005); http://dx.doi.org/10.1063/1.1850385 (3 pages) | Cited 2 times

Online Publication Date: 10 May 2005

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The exchange constants in spinel ferrites with S-state ions, including magnesium ferrite, lithium ferrite, and manganese ferrite, were calculated using modified Becke’s three-parameter density functional, where the percentage of Hartree–Fock exchange in total exchange was introduced as a variable parameter (w) to match the experimental results of exchange constants by controlling the localization and delocalization of the electrons. Consistently, the scaling factor of the 3d orbitals of ferric ions was also introduced as a variable parameter (α). From the calculation, the values of parameters w and α matching the experimental results of JAB (nearest-neighbor exchange constant between tetrahedral and octahedral sublattices) were concentrative, while those matching the experimental results of JAA (nearest-neighbor exchange constant inside tetrahedral sublattice) and JBB (nearest-neighbor exchange constant inside octahedral sublattice) were dispersive. Observing that JAB is dominant in most practical ferrimagnetic spinel ferrites and the current accuracy of the measurements of JBB and JAA may be insufficient to support more accurate conclusion, it is suggested that there may be an empirical universal law of parameters w and α for spinel ferrites with S-state ions.
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75.50.Gg Ferrimagnetics
75.30.Et Exchange and superexchange interactions
75.40.Mg Numerical simulation studies

Complex permittivity and permeability of barium and strontium ferrite powders in X, KU, and K-band frequency ranges

Adil Bahadoor, Yong Wang, and Mohammed N. Afsar

J. Appl. Phys. 97, 10F105 (2005); http://dx.doi.org/10.1063/1.1853633 (3 pages) | Cited 11 times

Online Publication Date: 10 May 2005

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This paper presents accurate results for the complex permittivity, ε = ε′−jε″ and permeability, μ = μ′−jμ″ of barium ferrite powder (BaFe12O19) and strontium ferrite powder (SrFe12O19), in the frequency range from 8.0 to 26.5 GHz. The complex permittivity and permeability are determined via the waveguide transmission/reflection (TR) technique and the waveguide cavity resonator (CR) technique at 25 °C and relative humidity <75%. Measurements reveal that the real permittivities of BaFe12O19 and SrFe12O19 are, respectively, 2.497<εBa′<2.678, and 2.597<εSr′<2.712. BaFe12O19 has an average real permeability μBa′ = 1.078 and SrFe12O19 has an average real permeability μSr′ = 1.063. The imaginary permittivities are respectively εBa″<0.081 and εSr″<0.077. The imaginary permeabilites are respectively μBa″<0.095 and μSr″<0.106.
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75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
77.22.Ch Permittivity (dielectric function)
78.70.Gq Microwave and radio-frequency interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic properties of Sc-substituted ytterbium iron garnet under high dc field (33 Tesla)

Maurice Guillot, Jean Ostorero, Gordon Armstrong, Fang Zhang, and You Xu

J. Appl. Phys. 97, 10F106 (2005); http://dx.doi.org/10.1063/1.1856753 (3 pages) | Cited 1 time

Online Publication Date: 10 May 2005

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Magnetic measurements were performed on Yb3Fe5−xScxFe5O12(YbIG:Sc), x = 0.5, single crystal platelets oriented along and perpendicular to the [111] crystallographic direction, in the 1.5–20 K temperature range in a magnetic field up to 330 kOe. Along the [110] and [100] axis H was limited to 230 kOe in the 4.2–300 K range. When H is parallel to [111] and [110] a first-order field induced transition are observed below about 10 K; the temperature variations of the transition field are very different. When H is applied along [100] a monotonous behavior is simply found. A noticeable anisotropy between the magnetic properties of the three samples remains present up to about 100 kOe. For the [111] sample the saturation is attained under 250 kOe below 10 K; the magnetic moment per Yb3+ ion that is deduced to be 1.78±0.05 Bohr magneton confirms the strong quenching of the orbital moment by the crystalline field. In the intermediary field range ( ≈ 100–220 kOe), there exists no more magnetic anisotropy. The magnetization that is proportional to the applied H is characterized by the onset of a field-induced magnetic structure; the Yb–Fe exchange constant is then determined. When H lies in the (111) plane, a strong M reduction is noted in the whole H domain; however, the transition field, the linear H Yb–Fe variation domain and the saturation field are the same as along the [111] direction.
Show PACS
75.50.Gg Ferrimagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
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