Specifics of determination of orientation magnetic phase transition characteristics in hematite using magnetoacoustic methods

The measurement results of the velocity of magnetoelastic waves in hematite corresponding to their quasi-phonon branch have been presented. The dependences of this velocity $(V)$ on the magnetic field $(H)$ at constant uniaxial pressure $P,(V_P(H))$, and on pressure $P$ at constant $H,(V_H(P))$, have been studied. In accordance with the existing theory of magnetoacoustic phenomena, dependences $V_P(H)$ and $V_H(P)$ should exhibit minima at the orientation phase transition points. These minima were found, but their coordinates on the plane $(P,H)$ did not coincide. The reasons of non-coincidence and requirements to the measurement accuracy are discussed, which yield possibilities of its use to determine characteristics of these transitions.