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[en] To make the transition from the quasi-long-range order in a chain of antiferromagnetically coupled S = 1/2 spins to the true long-range order that occurs in a plane, one can assemble chains to make ladders of increasing width. Surprisingly, this crossover between one and two dimensions is not at all smooth. Ladders with an even number of legs have purely short-range magnetic order and a finite energy gap to all magnetic excitations. Predictions of this ground state have now been verified experimentally. Holes doped into these ladders are predicted to pair and possibly superconduct. 51 refs., 6 figs
[en] The spontaneous magnetization m and the root-mean-square order parameter m0 of the Lieb-Mattis model for arbitrary temperature and spin values s are obtained. For the ratio r(T,s)=m/m0 the value r(T,s)=√3 is found. (author). 8 refs
[en] It is shown that the long-wavelength spin-wave spectrum of antiferromagnetic superconductors differs substantially from the usual spectrum. In the case of an easy-axis anisotropy, the spectrum should have a dip at a finite value of the wave vector
[en] It has been calculated the electronic band structure, density of states, band gap, total energy of the ideal and defective semi magnetic semiconductors Cd1-xMnxSe (0.01≤x≤0.06) by ab-initio method using the Functional Density Theory. It has been established that, with an increase in the concentration of Mn atoms, the band gap decreases. Vacancy-type defects lead to an increase in the band gap, a change in the total energy, and the formation of local levels in the band gap. It has been defined, that Mn atoms form magnetic moments, and the ferromagnetic state is more stable.
[en] A theory is derived for the antiferromagnetic resonance for an antiferromagnet in an intermediate state. In an intermediate state, the dependence of the resonant frequencies on the external field is strongly affected by the shape of the sample. Experimental results are interpreted