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  • 1
    Electronic Resource
    Electronic Resource
    Experimental determination of an effective demagnetization factor for nonellipsoidal geometries : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5742-5744 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a nonellipsoidal magnetic sample, the internal magnetic field Hint(r) is inhomogeneous even when a uniform external magnetic field Happ is applied to it. In such a case the elements of the demagnetizing tensor become position-dependent, N=N(r). The knowledge of the local demagnetization tensor is important for the analysis and design of devices using finite size and shape magnetic elements. The demagnetizing tensor elements can be calculated analytically and/or numerically, however, often a quick check of the extent of the inhomogeneity of the magnetization distribution of a sample, or a single approximate value of the demagnetizing factor for the given non-ellipsoidal geometry, would be satisfactory. Therefore a method to define and measure an effective demagnetizing tensor element Neff for rectangular and circular shapes has been developed. Experiments, performed on 2×4 mm2 yttrium iron garnet samples up to 220 μm thickness, show that the analytical approximation can be used to define an Neff. But even for a length/thickness ratio of 200, the thin film approximation still is in an error of 3.7%. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362236
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  • 2
    Electronic Resource
    Electronic Resource
    Enhanced coercivity due to a local anisotropy increase : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6106-6108 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In most of the cases, a local wall energy decrease, usually associated with defects, leads to domain wall pinning. Another mechanism for coercivity is to create local maxima in the anisotropy energy. It is observed that in epitaxial garnet crystals, locally enhanced anisotropy due to stress arising from iridium inclusions embedded in the substrate is the source of coercivity. By modifying our previous energy barrier model, the coercivity has been calculated as a function of the size and position of the iridium inclusions in the substrate. It is shown that the coercivity varies nonlinearly with inclusion size and depth in the substrate material, in agreement with experimental observation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355475
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature dependence of coercivity of epitaxial magnetic garnet films (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3827-3832 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of the coercivity Hc, magnetization, anisotropy, and domain wall energy was measured for SmGaYIG, SmCaGeYIG, and SmLuCaGeYIG epitaxial bubble garnet films from 100 K up to the Néel temperature TN(approximately-greater-than)400 K. Data were analyzed together with results published on similar samples on the basis of the theory of domain wall pinning by a random array of uniform defects and a good fit was observed in the form of H1/2c=H1/20 −CT2/3, where H0 and C are constants. The maximum average interaction force between defects and walls is 2.9×10−7 dyne, corresponding to the minimum interaction range equal to the wall width. The density of defects is in the range between 1014 and 1016 cm−3. The size and number of defects derived from the temperature dependence of Hc is in agreement with the microstructure of epitaxial garnets revealed by transmission electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335598
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  • 4
    Electronic Resource
    Electronic Resource
    Rotational and domain wall motion aftereffect in a patterned array of small particles (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7025-7027 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Aftereffect for magnetization processes by rotation and by domain wall motion was investigated on the same, single domain, two-state system of a square 2D (two-dimensional) array of garnet particles. Aftereffect measurements were performed magnetooptically. The particles are thermally stable, the particle energy is 10−6 erg compared to the thermal energy of 10−12 erg. No aftereffect of rotation switching of the system of "up" and "down" magnetized particles could be observed at room temperature. At increased temperatures thermally activated switching, very weakly depending on magnetic field, is observed. Each individual particle can be demagnetized into a metastable stripe domain structure. The barrier for DW (domain wall) motion is much lower than the barrier for rotation, and a significant aftereffect was measured on the same particles, demagnetized into a domain structure. The observed time dependence for DW aftereffect is exponential, M(t)/Ms=d* exp(−et), where d=0.04, and e=1/τ follows the increase of the magnetization with field, de/dH=0.021 /s/Oe. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372919
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  • 5
    Electronic Resource
    Electronic Resource
    Canted ferrimagnetism in Ca2+Sc3+ substituted yttrium-iron-garnet (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5656-5658 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of the magnetization of Y3−y−zCayLuzFe5−xScxO12 (0.6≤x≤1.2, 0≤y≤0.3, 0≤z≤0.9) epitaxial garnet films was measured from 4.2 K up to the Curie temperature. For x=0.7 and T≥50 K, 4πMs is enhanced by about 10% compared to the magnetization of Sc0.7 YIG. At T〈50 K, a reduction of the magnetization, increasing with increasing substitution, was observed for all the measured samples. Agreement between the experimental results and molecular field models was obtained by taking into account the canting of the unsubstituted sublattice, the presence of charge compensating Fe4+ ions, a low-temperature ordering of Fe3+ ions with less than two magnetic nearest neighbors, and assuming a lattice parameter-dependent exchange interaction ratio with d(Jdd/Jad)/da =28 nm.−1 For x=1.2 and T〈10 K the magnetization can be influenced by cooling through the Curie point in a magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342261
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetization anomalies and temperature-dependent hole localization in the Ca2+Fe4+Ga3+: yttrium iron garnet system (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3107-3109 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The measurement of the temperature dependence of the magnetization, Ms, between 4.2 and 300 K of epitaxial films of Y3+3−xCa2+xFe3+5−y−x' Ga3+yFe4+x'O2−12, with x〈0.4 and 0≤y〈1.6, has shown low-temperature deviations from the molecular field theory of a two-sublattice Néel model, generally applicable to yttrium iron garnet with nonmagnetic substitutions. Molecular field calculations of M(x,y,T) have been performed, assuming a temperature-dependent concentration of Fe4+ ions due to the gradual localization of the uncompensated hole at the tetrahedral Fe3+ sites with the lowering of the temperature. The Fe4+ ions are assumed to form a third magnetic sublattice, which is ferromagnetically coupled to the octahedral Fe3+. The hole localization energy is observed to be on the order of 1–4 meV. The calculations are in good agreement with the experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340857
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  • 7
    Electronic Resource
    Electronic Resource
    Excitation effects in excess Ca-doped epitaxial CaGe:YIG garnets (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 3552-3554 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of light and electric field on the electrical transport properties of p-type CaGe:YIG epitaxial films, having 0.1 at. f.u. excess Ca2+, were investigated from 30 to 340 K by measurements of dc conductivity, space-charge-limited current, and thermally stimulated current decay. The room-temperature conductivity of the films is of the order of 10−6 mho/cm, the mobility of the holes is 0.5 cm2/V s, and the density of charge carriers is 1012/cm3. The low-temperature conductivity of the films can be increased by six orders of magnitude under the effect of light (∼25 mW/cm2) and electric field (≤104 V/cm) at temperatures below 140 K. This photo- and electric-field-excited high conductivity state can be destroyed by thermal excitation at higher temperatures. It is assumed that below 200 K the holes are localized at Ca2+-Fe4+ centers which constitute an impurity band. Electrons excited from the valence band are trapped under the influence of the field at centers, formed probably by oxygen vacancies. The holes left in the valence band contribute to the high conductivity at low temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338721
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of ion implantation on stripe- and bubble-domain coercivity (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2119-2124 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The static coercivity of stripe and bubble domains in 5-μm (YSmCa)3(FeGe)5O12 epitaxial garnet films was measured by the oscillating-wall method. The dependence of coercivity on Ne+ implantation energy and dosage was investigated. In a wide range of energy and dosage, implantation was found to eliminate hard bubbles and decrease bubble coercivity by 25%; the decrease is a measure of the contribution of Bloch lines to coercivity. The average number of Bloch lines n in bubble walls was determined from static coercivity as 37≤n≤62, n increasing with quality factor Q. Bubble coercivity was always found to be higher than stripe coercivity measured by the same method. Implantation has no measurable effect on apparent stripe coercivity which may be a consequence of the lower Bloch line density of stripes relative to bubbles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337018
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  • 9
    Electronic Resource
    Electronic Resource
    The mechanism of the high conduction state in the Ca2+Ge4+:YIG system (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3306-3308 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating epitaxial garnet films of p-type Ca2+Ge4:YIG can be excited to a high conduction state (HCS) under the effects of light and electric field. To clarify the mechanism of the HCS, epitaxial films of Ca2+:YIG, Ge4+:YIG, Ca or Ge excess Ca2+Ge4+:YIG have been investigated. dc I-V characteristics were measured in electric fields up to 105 V/cm, with and without light. Thermopower and deep level transient spectroscopy (DLTS) were measured between 140 and 300 K. At low electric field the conduction is ohmic. As the electric field is increased a square-law dependence is observed and at a critical field, on the order of 105 V/cm and whose value is sensitive to the frequency and intensity of the light, a negative resistance state is formed in Ca:YIG and CaGe:YIG (both p- and n-type) films, and in this region the sample suddenly transforms to the HCS. A very slow transformation to the HCS can also be observed at lower electric fields, on the order of 104 V/cm, by keeping the electric field constant and illuminating the sample with light on the order of 10 mW/cm2 intensity. Thermopower and DLTS data indicate that electrons located in compensated acceptor states are removed in the HCS. The presence of a sufficient number of compensated acceptors and oxygen vacancies serving as repulsive traps is a necessary condition for the formation of the HCS. The transition to this HCS is then proposed to be a process where electrons are transferred to the repulsive traps located below the conduction-band mobility edge. This trapping process lowers the Fermi level toward the valence band.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340819
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  • 10
    Electronic Resource
    Electronic Resource
    Sample size effect in coercivity measurement of epitaxial magnetic garnet films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1694-1700 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The full set of characteristic parameters of epitaxial garnet films was measured as a function of the sample size from about 2000 to 5 mm2. The type of domain structure, width of the stripe domain period, characteristic material length, domain wall energy, and anisotropy did not change within the error of measurement on reducing the sample size. The bubble domain collapse field decreased by about 2.5%, and the domain wall coercivity was measured and found to have decreased—almost by an order of magnitude. The experiments showed the lack of dependence of coercivity on the domain wall length. The coercivity and collapse field are suggested as being related to the sample dimensions via the sample-size-dependent derivatives of the total free energy with respect to the domain wall positions. The assumption of the direct effect of the free energy derivatives on the coercivity is supported by a model experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339904
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