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  • 1975-1979  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    General alloy analogs of itinerant magnetic systems (1977)
    Springer
    The European physical journal 28 (1977), S. 31-36 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Magnetically disordered, strong correlated itinerant electron systems are studied within the Hubbard model. Following an “alloy analogy”, the approximated system hamiltonian contains local vectoral magnetic fields at the atomic sites, which can be oriented into all space directions. The statistical system of the localized magnetic moments (due to the fields) is treated by the aid of a generalized CPA-technique. Supposing a macroscopic magnetic structure of sublattice antiferromagnetism, the formation of incomplete antiferromagnetic ordering of the localized moments is examined. The results show, that the electron density plays an essential roll for the question, whether or not it is possible to go beyond the pure (itinerant) antiferromagnetic state. Including the results of earlier papers for homogeneous macroscopic magnetic structure, on the whole scale of electron densities it is summed up (at zero temperature), where the different states (without-, with incomplete- or with complete magnetic order) are able to exist. It is shown, for fixed density respectively, which different phases are passed through on changing the coupling constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01313946
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  • 2
    Electronic Resource
    Electronic Resource
    Partial disorder in itinerant antiferromagnets—electronic density of states (1976)
    Springer
    The European physical journal 25 (1976), S. 177-180 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We examine the behaviour of magnetically disordered, strong correlated electron systems for the case of antiferromagnetic arrangements of the electron-spins. Preceding calculations in earlier papers for homogeneous systems yielded a state, where localized magnetic moments at the atomic sites were built up. The moments showed a partial homogeneous magnetic order in the so called “mixed state”. In this contribution we realize equivalent conditions for antiferromagnetism: After a coordinate transformation in an approximated Hubbard-Hamiltonian, it is possible to use a CPA-like method for statistical distributions of the vectoral localized moments in the same way as for homogeneous systems. As an example we study at first the quasi-particle density of states for a Lorentz-distribution of the moments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320178
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  • 3
    Electronic Resource
    Electronic Resource
    Exact results for the dynamics of one-dimensional spin-systems (1976)
    Springer
    The European physical journal 25 (1976), S. 181-187 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this contribution we discuss the spin-dynamics of anisotropic one-dimensional spin 1/2X-Y-chains in a magnetic field. For special values of the parameters we solve the equation of motion for several spin-operators exactly. These results we use to calculate longitudinal and transverse dynamical correlation functions at temperatureT=∞, for an Ising chain in a transverse field also the first-order high-temperature correction is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01320179
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  • 4
    Electronic Resource
    Electronic Resource
    Exact results on random bond Ising Chains in magnetic fields (1978)
    Springer
    The European physical journal 31 (1978), S. 237-245 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this contribution we present exact results on the random bond Ising Chain in a magnetic field. The original problem is reduced to the solution of a functional equation for a certain probability distribution, which can be used to evaluate thermodynamics and correlation functions. We give a sufficiently accurate solution for low temperatures, which yields the complete low-temperature behaviour. Comparison is made with different Monte-Carlo-calculations performed on this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01352348
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  • 5
    Electronic Resource
    Electronic Resource
    The transverse correlation function of anisotropicX—Y-chains: Exact results atT=∞ (1977)
    Springer
    The European physical journal 26 (1977), S. 245-252 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this contribution we present exact results for the transverse dynamical correlation function of anisotropic spin 1/2X—Y-chains in the presence of magnetic fields at temperatureT=∞. Our results are obtained by an application of a new theory of block-Toeplitz determinants also developed in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312930
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  • 6
    Electronic Resource
    Electronic Resource
    Partial ordered homogeneous magnetic moments in the Hubbard-model (1976)
    Springer
    The European physical journal 24 (1976), S. 129-134 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this contribution, we study the behaviour of magnetically disordered electron systems. In a model with localized magnetic fields at the atomic sites, a CPA-like method, which has regard for the vector character of the fields, is used to examine the case where the localized fields, which correspond to atomic magnetic moments, are distributed statistically. In an example for a non-isotropic distribution of the fields, we construct a system state with partial homogeneous order of the localized fields (or moments). The ordering behaviour of the system and the comparison of the new magnetic state with pure magnetic and non-magnetic band states and with the non-magnetic state of (isotropic) stochastic distribution of the localized fields is discussed. With this paper we are able to introduce typical properties of localized models into a band model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312881
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  • 7
    Electronic Resource
    Electronic Resource
    Thermodynamic properties of extended Hubbard chains (1975)
    Springer
    The European physical journal 22 (1975), S. 397-399 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this contribution we discuss the thermodynamic behaviour of Hubbard chains with an additional site-diagonal interaction. It is shown rigorously that the strong coupling limit is equivalent to a generalized anisotropic Heisenberg system, which in some recently discussed limiting cases degenerates to an Ising orX-Y system. The whole procedure also works for a collection of chains with interchain interaction, thus it is not restricted to strictly one-dimensional systems. The effect of a magnetic field is discussed, and the results are compared with a recent perturbation approach by using numerical results for the anisotropic Heisenberg chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312812
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