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[en] The exponential growth of maximum energy product that prevailed in the 20th century has stalled, leaving a market dominated by two permanent magnet materials, Nd2Fe14B and Ba(Sr)Fe12O19, for which the maximum theoretical energy products differ by an order of magnitude (515 kJ m−3 and 45 kJ m−3, respectively). Rather than seeking to improve on optimized Nd–Fe–B, it is suggested that some research efforts should be devoted to developing appropriately priced alternatives with energy products in the range 100–300 kJ m−3. The prospects for Mn-based hard magnetic materials are discussed, based on known Mn-based compounds with the tetragonal L10 or D022 structure or the hexagonal B81 structure. (paper)
[en] In this contribution the phenomenological theory for the tunnelling magnetoresistance phenomenon observed in granular perovskite manganese systems is developed using Landauer ballistic transport concept. It was shown that the field dependence, magnitude and derivative of magnetoresistance ratio observed experimentally are well reproduced by the presented theory.
[en] Initial data on the hydrogen-isotopic compositions in hydrous Mn minerals from various occurrences fall in a wide range from -298 to -84per thousand, relative to SMOW. deltaD-values of todorokite and cryptomelane from Tertiary deposits show -89 and -150per thousand. 10 A-manganite and delta-MnO2 from deep-sea nodules have relatively restricted deltaD-values ranging from -96 to -84per thousand. The deltaD-values for manganese bog ores from recent hot springs show almost -105per thousand. It is recognized that the isotopic values obtained for the deep-sea nodules and recent bog ores are slightly different ranged. Manganite and groutite are unique in their hydrogen-isotopic compositions, having the most depleted deltaD-values ranging from -298 to -236per thousand. MnO(OH) minerals are more deuterium-depleted hydrous minerals than any other hydrothermal minerals from various ore deposits. Hydrogen-isotope fractionation factors between manganite and water were experimentally determined to be 0.7894, 0.7958 and 0.8078 at 1500, 2000 and 2500C respectively. The present experimental results indicate that if manganites were formed at temperatures below 2500C, under isotopic equilibrium conditions most of the manganite mineralization in the Tertiary manganese deposits must have precipitated from meteoric hydrothermal solutions. (Auth.)