Magnetovolume Effects in MnAs. Role of Space Spin Correlations

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The results of experimental separation of the various contributions to the MnAs volume magnetostriction in a wide range of temperatures are presented. This separation is made by determination of different magnetovolume constants from forced volume magnetostriction and susceptibility measurements using a phenomenological theory, in which both itinerant electron and local moment characters are taken into account. It is shown that the main contribution to the spontaneous magnetovolume effect in the ferromagnetic region and to the discontinuous volume change at the Curie temperature is the exchange striction. The band contribution connected with the change of the local moment magnitude in these cases is small. It is obtained that there are strong spin‐spin correlations near and above the Curie point, so the molecular field approximation often used for the description of the MnAs magnetic behavior is inadequate in this temperature region. The results obtained are used to estimate the temperature variation of the local magnetic moment magnitude in MnAs.