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  • 1
    Electronic Resource
    Electronic Resource
    Zone-center magnons in dilute magnetic semiconductors : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6112-6113 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A calculation of the frequency of a zone-center magnon in a dilute magnetic semiconductor is outlined. It is based on the moments of the imaginary part of the dynamic spin susceptibility. Results are obtained at low temperatures for Cd1−xMnxTe in the zero- and high-magnetic-field limits. Good agreement with experiment is found assuming that (1) the dominant anisotropy mechanism is the Dzyaloshinski–Moriya interaction and (2) nearest-neighbor Mn spins are not colinear in the zero-field ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347783
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  • 2
    Electronic Resource
    Electronic Resource
    Antiferromagnetic magnons in diluted triangular and Kagomé lattices (abstract) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5657-5657 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical results are presented for the local field distribution and the distribution of linearized magnon modes in diluted triangular and Kagomé lattices. A nearest-neighbor antiferromagnetic Heisenberg spin Hamiltonian is assumed, and the linearization is carried out with respect to classical ground states obtained by means of an energy minimization algorithm.1 In the case of the triangular lattice, the density of states associated with a 20% vacancy concentration is used to calculate the magnon contribution to the specific heat. With an exchange integral inferred from the Curie–Weiss constant, quantitative agreement is obtained with the experimental results for La0.2Gd0.8CuO2 reported by Ramirez et al.2 over the interval 0.1 K≤T≤0.2 K. The behavior of the diluted Kagomé lattice is compared with that of the triangular array. In contrast to the latter, the local fields in the diluted Kagomé lattice take on the discrete values 2JS, JS, and 0. In the case of a 14% vacancy concentration, the distribution of magnon modes resembles that of the fully occupied array with a noncoplanar ground state. The relevance of these results to the behavior of SrCr8Ga4O19 is discussed.3
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353630
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  • 3
    Electronic Resource
    Electronic Resource
    Step-induced magnetic-hysteresis anisotropy in ferromagnetic thin films (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 3150-3153 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the quasistatic magnetic hysteresis of ferromagnetic thin films grown on a vicinal substrate, using Monte Carlo simulations within a two-dimensional XY model. Intrinsic in-plane anisotropy is assigned to surface sites according to their local symmetry. The simulated hysteresis loops show a strong anisotropy: the coercive field is the largest when the external field is along the step direction and vanishes when the external field is perpendicular to the step direction. In general, the coercivity increases with increasing step density, but displays a more complex dependence on film thickness. The simulations also suggest that the mechanism for the magnetization reversal is coherent rotation. These results are in good agreement with experiments. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1433179
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  • 4
    Electronic Resource
    Electronic Resource
    Freezing of the extended state in the random local field theory of Ising spin glasses with long range interactions : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6143-6145 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The onset of spin glass freezing in dilute Ising systems with long range interactions is investigated within the framework of a random local field approach (previously developed for disordered ferromagnets and ferroelectrics) with the use of numerical simulations. The problem reduces to the diagonalization of an N×N random matrix, N being the number of spins in the simulation, whose elements depend on the spin–spin interaction and temperature. We identify the onset of spin glass freezing with the temperature at which this boundary eigenvalue separating localized and extended states is equal to one. Numerical simulations give a reasonable value of the freezing temperature for dilute RKKY spin glasses and reproduce its linear concentration dependence in agreement with the scaling relation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362051
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  • 5
    Electronic Resource
    Electronic Resource
    Exchange stiffness of Ca-doped YIG : 38th Annual Conference on Magnetism an Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5517-5519 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An effective medium theory for the zero-temperature exchange stiffness of uncompensated Ca-doped YIG is presented. The theory is based on the assumption that the effect of the Ca impurities is to produce strong, random ferromagnetic interactions between spins on the a and d sublattices. In the simplest version of the theory, a fraction, x, of the ad exchange integrals are large and positive, x being related to the Ca concentration. The stiffness is calculated as function of x for arbitrary perturbed ad exchange integral, Jxad. For Jxad(approximately-greater-than)(1/5)||8Jaa+3Jdd||, with Jaa and Jdd denoting the aa and dd exchange integrals, respectively, there is a critical concentration, Xc, such that when x(approximately-greater-than)Xc, the stiffness is complex. It is suggested that Xc delineates the region where there are significant departures from colinearity in the ground state of the Fe spins. Extension of the theory to a model where the Ca doping is assumed to generate Fe4+ ions on the tetrahedral sites is discussed. Possible experimental tests of the theory are mentioned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355674
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of electron paramagnetic resonance experiments in colossal magnetoresistance materials : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6949-6951 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis is given of recent electron paramagnetic resonance (EPR) experiments in manganite materials displaying colossal magnetoresistance behavior. These experiments have established that in highly homogeneous samples characterized by a single resonance line, the EPR linewidths above the critical region associated with the paramagnetic–ferromagnetic transition are inversely proportional to Tχ(T), where χ denotes the susceptibility. This behavior indicates that the linewidth does not reflect a coupling to the lattice vibrations but rather is caused by a spin-only mechanism. The possibility that the linewidth arises from the dipolar interaction is assessed using an effective interaction model. On the basis of the model calculation, it is concluded that the dipolar interaction is probably too weak to account for the observed broadening and that the linewidth most likely arises from tetragonal and orthorhombic distortions of the octahedral crystal field at the sites of the Mn ions. The EPR linewidth in samples with very low concentrations of Mn4+ ions is expected to vary with temperature as [Tχsp(T)]−1, where χsp(T) is the susceptibility of the ferromagnetically coupled spin polaron. By measuring the temperature dependence of the linewidth, one may be able to determine the temperature dependence of the polaron susceptibility. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367538
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  • 7
    Electronic Resource
    Electronic Resource
    Microscopic theory of magnetic excitations in ferromagnets with random anisotropy axes (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5627-5629 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a microscopic theory of the harmonic magnetic excitations in ferromagnets with random anisotropy axes. The theory is analogous to the theory of excitations in spin glasses developed by Walker and Walstedt, with the difference that the disorder arises from the anisotropy rather than the exchange interaction. We report the results of numerical calculations of magnon density of states and the ferromagnetic resonance frequency for a model system where the spins occupy sites on a fcc lattice. The exchange interaction is between nearest neighbors, and the anisotropy axis varies randomly from site to site with no correlation between different sites. Data are obtained with a range of values of the ratio of the anisotropy to the exchange interaction in both the zero-field and high-field limits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342303
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  • 8
    Electronic Resource
    Electronic Resource
    Spin dynamics in Zn1−xMnxTe (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3297-3299 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: First results of inelastic neutron scattering studies of quasiharmonic magnons in Zn1−xMnxTe are reported. Measurements carried out on two single-crystal samples with x=0.65 and x=0.41 at T=4.2–5.0 K revealed broad excitation modes, which were in excellent agreement with the results of theoretical modelling. Results for x=0.65 yield JNN=(7.9±0.2) K which is the first determination of the nearest-neighbor exchange constant in Zn1−xMnxTe in this x region. Data taken at higher temperatures showed only weak renormalization of the energy spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340816
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  • 9
    Electronic Resource
    Electronic Resource
    Instabilities of spin waves in parallel-pumped easy plane ferromagnets (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4151-4153 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By applying the S-theory formalism of Zakharov et al. to a microscopic hamiltonian with uniaxial easy plane anisotropy, we arrive at a set of equations for the system that describe the spin waves and their mutual interactions. The parameters in the theory are related to the various interaction constants of the microscopic hamiltonian. Numerical studies of this system of equations indicate that the stationary states are ones where all spin-wave pair correlation functions have the same phase. The phenomenon of phase locking is universal, independent of the mode of approach to equilibrium. It is found that there is no dependence on the number of modes (up to 100) for the above behavior. This, together with the form of the equations, indicates that a similar result should hold for a macroscopic number of modes. Results for the stationary magnon population are presented. In the phase-locked regime, the approach to a stationary state is governed by a pair of coupled first-order differential equations. Linearizing these equations about the stationary points, we find that the approach to equilibrium involves purely exponential decay just above threshold, and, at higher power levels, we have damped oscillatory decay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340523
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  • 10
    Electronic Resource
    Electronic Resource
    Equation of state for classical hard-particlelike fluids (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5027-5030 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We extend earlier studies of the equation of state of classical hard-particle fluids to potentials where there is an attractive tail in addition to a repulsive hard core. Like the earlier work, the approach is based on the arbitrary point, nearest-neighbor probability density function. In the high temperature (hard-particle) limit, a parametrization of the integrated distribution is introduced. By matching the parameters against the coefficients in a seven-term virial expansion, we obtain an equation of state that is in excellent agreement with the results from Monte Carlo, molecular dynamics calculations in both two and three dimensions. The theory is extended to finite temperatures by treating deviations from the hard-particle limit as small corrections that can be evaluated using hard-particle distribution functions. A comparison is made with the results from a five-term finite temperature virial expansion for a three-dimensional hard-particle system with a square well attractive potential. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470589
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