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  • 1
    Electronic Resource
    Electronic Resource
    Comment on "Anisotropy studies of molecular-beam-epitaxy-grown Co(111) thin films by ferromagnetic resonance'' [J. Appl. Phys. 75, 6492 (1994)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5484-5485 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic free energy expression E used to calculate ferromagnetic resonance frequencies by F. Schreiber et al., J. Appl. Phys. 75, 6492 (1994) is examined. The expression is correct for hexagonal site symmetry films but not for any type of cubic symmetry film. The correct expression, including both K1c and K2c anisotropy contributions, for E with H in the basal plane of a (111) film is given in the text. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359251
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  • 2
    Electronic Resource
    Electronic Resource
    Coordinated RHEED, XRD, and FMR investigations of MBE grown Co–Cu (100) superlattices : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4787-4789 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A sequence of fcc, 〈100〉 oriented, [Co (50 A(ring))–Cu (X)] superlattices with X=25–200 A(ring), was grown by molecular beam epitaxy on Cu(100)/Si(100) substrates. In-plane 33.4 GHz ferromagnetic resonance (FMR) data were analyzed to determine the perpendicular uniaxial magnetic anisotropy field (Hu) and cubic anisotropy field contributions. The Hu values were found to be negative, indicating that the film normal is a magnetic hard axis. The magnitude of Hu depended on the Cu layer thickness. Superlattice x-ray-diffraction and reflection high-energy electron-diffraction patterns were analyzed. The measured strain data for Co superlattice layers, in combination with known elastic and magnetostriction constants for bulk fcc Co, yield calculated strain-induced Hu values which agree well with those obtained from the FMR. The observed Hu values, which are affected by the Cu layer thickness, approach a constant for Cu thickness ≥100 A(ring). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361673
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic properties of carbon-coated rare-earth carbide nanocrystallites produced by a carbon arc method : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5879-5881 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon-coated gadolinum and holmium carbide nanocrystallites have been generated using a modification of the Huffman-Krätschmer carbon arc process. Bulk amounts of these particles were isolated from the other by-products using a magnetic field gradient. Transmission electron microscopy revealed the presence of 10–50 nm diameter crystallites coated with numerous graphitic layers. The nanocrystallite phases were identified as Gd2C3 and Ho2C3, respectively, by x-ray and electron diffraction. Magnetization measurements were performed using a superconducting quantum interference device magnetometer between ±5 T at temperatures ranging from 4 to 200 K. The magnetization curves were shown to scale as a function of H/T. The RE3+ sites in RE2C3 have C3 site symmetry. For Gd2C3 the universal curve was fit with a Brillouin function consistent with the Gd3+ free-ion ground-state values of J=7/2 and g=2. The 5I8 Ho3+ free-ion ground state is split, presumably due to a C3 symmetry crystal field. Consequently, for Ho2C3 the Ho3+ free-ion parameters could not be used to fit the experimental data. Empirical fits to the Brillouin function yield a reduced moment of 7.5μB, compared to the free-ion value of 10.6μB. A similarly reduced moment was observed in holmium-containing endohedral fullerenes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355547
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic properties of carbon-coated, ferromagnetic nanoparticles produced by a carbon-arc method : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5882-5884 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Krätschmer–Huffman carbon-arc method of preparing fullerenes has been used to generate carbon-coated transition metal (TM) and TM-carbide nanocrystallites. The magnetic nanocrystallites were extracted from the soot with a magnetic gradient field technique. For TM=Co the majority of nanocrystals exist as nominally spherical particles, 0.5–5 nm in radius. Hysteretic and temperature-dependent magnetic response, in randomly and magnetically aligned powder samples frozen in epoxy, correspond to fine particle magnetism associated with monodomain TM particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature TB. Below TB, the temperature dependence of the coercivity can be expressed as Hc=Hc0[1−(T/TB)1/2], where Hc0 is the 0 K coercivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355548
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  • 5
    Electronic Resource
    Electronic Resource
    Calculation of magnetic moments in Ho2C3 nanocrystals : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6307-6309 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A general approach to the computation of effective magnetic moments in rare-earth carbides is described, and details of this calculation for Ho3+ ions in Ho2C3 are presented. This calculation is designed to explain the reduced magnetic moments, relative to free ion values, measured by dc SQUID magnetometry for Ho2C3 nanocrystals. Crystal-field splittings of the rare-earth ion in a particular symmetry site are determined by the operator equivalent method. Using the eigenvalues and eigenfunctions of the crystal-field Hamiltonian, the effective magnetic moment is then determined. For Ho3+ ions in Ho2C3, this method predicts a reduced magnetic moment, but the degree of reduction depends on the energy-level splittings and, therefore, the temperature. This magnetic moment is compared with previous experimental results, and the implications of the formal carbon charge, screening, and temperature are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358535
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  • 6
    Electronic Resource
    Electronic Resource
    Stress-induced anisotropy in Co-Cr thin films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2917-2919 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A modified Varian dc magnetron sputtering system was used at an Ar pressure of 2 mTorr to prepare a sequence of 500-nm-thick Co78Cr22 films. From run to run the substrate temperature Ts was varied from close to room temperature to an upper limit of 300 °C. With a 33-GHz ferromagnetic resonance (FMR) spectrometer the effective anisotropy field, HKeff, was measured for films both as-deposited and removed from the substrate. The differences in effective field, ΔHKeff, were attributed to stress-induced anisotropy. The stress σ was determined by the disk flexure method. From σ and ΔHKeff we determined the magnetostrictive constant, Aλs. Usually A is assigned the value 3/2. p-type ("bulk'') Co-Cr is characterized by a negative λs, n1-type ("transition layer'') by a positive λs. Consequently, the tensile-type stress associated with our deposition scheme increases the positive effective anisotropy of p-type film constituents (by as much as 50%) and also increases (in a negative sense) the negative effective anisotropy of n1-type film constituents (by as much as 20%)! Since the relative p- and n-type proportions vary with Ts, the "average'' λs found by conventional methods would vary correspondingly. Also, with the addition of 4πMs data, we determine the intrinsic magnetocrystalline anisotropy fields of the film constituents. At Ts =155 °C the intrinsic p-type magnetocrystalline anisotropy field is 85% that of pure cobalt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340956
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  • 7
    Electronic Resource
    Electronic Resource
    Domain mode ferromagnetic resonance studies in bismuth-substituted magnetic garnet films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5483-5485 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bismuth-substituted magnetic garnet films, formulated so as to have a low magnetic quality factor Q, were grown from a bismuth-based melt using liquid-phase epitaxy. The lowest Q achieved was about 0.2. Such samples were observed to support parallel stripe domain structure and were theoretically predicted to have an "in-phase'' domain mode ferromagnetic resonance response at frequencies as low as 250 MHz. Such "in-phase'' resonances, along with the higher-frequency "out-of-phase'' mode, were observed experimentally with a variable radio frequency/fixed dc field ferromagnetic resonance spectrometer. The data, which were taken as a function of dc in-plane field, were found to be in good agreement with the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342354
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  • 8
    Electronic Resource
    Electronic Resource
    FMR in evaporated single and multilayer thin Fe films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5760-5762 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used ferromagnetic resonance (FMR) at 33 GHz to study the properties of a number of evaporated thin Fe film systems. Values for effective anisotropy field HKeff , g value, and exchange constant A were derived. For Fe on glass, ||HKeff || was found to increase with increasing thickness. These changes were attributed to stress which decreased with film thickness. The presence of a Cu or a Ti underlayer did not seem to affect HKeff for films grown at room temperature. However, Fe/Ti/glass films made at higher substrate temperatures, Ts, did show an increase in ||HKeff ||. The appearance of a spin-wave mode in the Fe films enables us to compute the exchange constant A for Fe, A=(2.12±0.14)×10−6 ergs cm−1. The coupling between two thin Fe films through an intervening Cu layer was investigated. A model predicting the number and position of the peaks in the spectrum as a function of coupling is presented. From experiment it was observed that the coupling remains almost constant through the 50–5-nm Cu thickness range but rises sharply at 2-nm Cu thickness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342250
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  • 9
    Electronic Resource
    Electronic Resource
    The investigation of the process of microwave bubble generation in bubble material (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4609-4615 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first observation of the process of magnetic bubble generation by microwave excitation has been made. A high-speed optical sampling microscope system was employed to sense the evolution of the bubble with time. The dependence of the microwave power threshold for bubble generation on experimental conditions such as microwave frequency, microwave pulse width, and dc bias field are reported. Magnetic garnet films with the composition Y1.92Sm0.1Ca0.98Fe4.02Ge0.98O12 were used as our experimental samples. The experimental results are not consistent with the theoretical predictions of the Seagle coherent rotation model for bubble generation. We find that the magnetization in the area driven by the strong microwave field responds rather noncoherently. Nucleation centers, which may be too small to be seen optically, are formed first. Under appropriate conditions, these centers may enlarge to a full size bubble. As examples, with a bias field setting of 65 Oe and the microwave frequency set at 550 MHz, about 25.5 dBm of power are required to generate a bubble from a 60-ns-long pulse; only 20.5 dBm are required if a 12-μs pulse is applied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340139
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  • 10
    Electronic Resource
    Electronic Resource
    Spin-wave FMR in annealed NiFe/FeMn thin films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3808-3810 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic resonance (FMR) investigations have been made at 33 GHz on as-deposited and on annealed bilayer NiFe/FeMn thin films. Supplemental investigations were made at 9 GHz. Following a 350 °C anneal, for 1 h or longer in duration, the NiFe FMR spectrum was found to be characterized by a sequence of spin-wave resonance (SWR) modes. The behavior of the SWR modes is in accord with the presence of a thin ferromagnetic layer at the NiFe/FeMn interface with magnetization different from the bulk. Transmission electron microscopy (TEM) examinations indicate that annealing promotes formation of an interdiffused layer at the NiFe/FeMn interface and favors NiFe grain growth. Magnetic field limitations precluded FMR at 0° (perpendicular) field orientation. At various field orientations below the critical angle, the resonant fields, Hn, were found to vary with mode number n as n2. Also, for n〉1, the FMR-SWR linewidth ΔHn has a component varying as n2. From the 33-GHz 16° orientation data, the exchange constant A is computed to be (1.03±0.15)×10−6 erg/cm. The application of an in-plane magnetic field during anneal produces a reduction of the SWR mode intensities and a broadening of the principal peak. A perpendicular magnetic field had little effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340621
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