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The effect of minor changes in lattice parameters and Mn 3+ /Mn 4+ ratios on the magnetoresistive and related properties of the La-Er-Ca-Mn-O perovskite system have been investigated. The latter is found to be the more important factor in determining the magnetotransport properties of these materials. One composition has been prepared by both the standard ceramic method as well as a sol-gel technique. Although the general features of the magnetotransport properties of these two samples were very similar, the magnetic properties showed significant differences. Experimental results are explained on the basis of a spindependent mechanism which is related to lattice distortion.

The experimental knowledge on interlayer potential of graphenites is summarized and compared with computational results based on phenomenological models. Besides Lennard-Jones approximation, the Mie potential is discussed, Kolmogorov-Crespy model and equation of Lebedeva et al. An agreement is found between a set of reported physical properties of graphite (compressibility along c-axis under broad pressure range, Raman frequencies for bulk shear and breathing modes under pressure, layer binding energies), when a proper choice of model parameters is made. It is argued that the Kolmogorov-Crespy potential is the preferable one for modelling. A simple method of fast numerical modelling, convenient for accurate estimation of all these discussed physical properties is proposed. It is useful in studies of other van der Waals homo/heterostructures.

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In many cases, the critical-state theory can be treated as a suffi ciently accurate approximation for the modelling of the magnetic properties of superconductors. In the present work, the magnetostrictive hysteresis is computed for a quite general case of the modified KimAnderson model. The results obtained reproduce many features of the giant magnetostriction (butterfly-shaped curves) reported in the literature for measurements made on single-crystal samples of the hightemperature superconductor Bi 2 Sr 2 CaCu 2 O 8 . It is shown that addition of a contribution to the magnetostriction in the superconducting state which is of similar origin as in the normal state, offers a broader phenomenological interpretation of the complex magnetostriction hysteresis found in such heavy-fermion compounds as U P t 3 , U Ru 2 Si 2 or U Be 13 .