THE DETECTION OF MAGNETIC PHASE-TRANSITIONS IN SINGLE-CRYSTALS OF ERBIUM AND ERBIUM-THULIUM BY ELECTROMAGNETIC ACOUSTIC TRANSDUCERS

Measurements of ultrasonic shear wave velocity as a function of temper ature and applied magnetic field have been performed on single crystal s of Er and Er91.6%Tm8.4%. Electromagnetic acoustic transducers (EMATs ) are used to generate and detect the in-plane radially polarized shea r wave. The shear wave is propagated down the c axis of the hexagonal close packed single crystal samples. The EMAT acoustic coupling effici ency has been observed to increase close to the magnetic phase transit ion temperatures, showing the dominance of the magnetoelastic interact ions over the applied-field-dependent Lorentz force mechanism in these samples. Measurement of the EMAT acoustic coupling efficiency is iden tified as a promising technique for identifying magnetic phase transit ions. Because the ultrasound measurement technique is a non-contact on e, problems associated with acoustic couplants are avoided.