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We report here on low temperature magnetic relaxation in the erbium orthoferrite ErFeO 3 . The variation of magnetic viscosity, S ≡ ∂M / ∂ / ∂ ln t , with temperature shows three different regimes below 40 K. The most remarkable is that at T ≤ 3 K where S(T) remains constant suggesting the occurrence of macroscopic quantum tunneling of the magnetization.

This paper describes the preparation of rutile-type V/Sb mixed oxide (vanadium antimonate) with the ball-milling (mechano-chemical) method starting from single metal oxides, as well as the comparison with a similar system prepared by the co-precipitation method. Samples were tested as catalysts for the gas-phase ammoxidation of propane to acrylonitrile. The mechano-chemical method allowed the preparation of the rutile-type mixed oxide characterized by smaller crystallite size than the catalyst prepared by co-precipitation and calcined at 450 °C. The calcination at 700 °C of the sample prepared by the mechano-chemical method led to a crystalline vanadium antimonate characterized by a higher concentration of cationic defects than the corresponding calcined sample prepared by co-precipitation. This led to a considerably higher activity in propane ammoxidation, but to a lower selectivity to acrylonitrile.