ULTRASONIC PROPAGATION IN EUO

The attenuation of 10 to 90-MHz longitudinal and shear ultrasonic waves propagating along the [100] and [110] directions of EuO single crystals was measured between 63° and 78°K. At zero applied magnetic field, the attenuation was constant above the Curie temperature, TC=70°K, but increased as the temperature was lowered through TC. The increase in attenuation was much greater for the shear modes than for the longitudinal modes. Preliminary experiments at 4.2°≤T≤78°K with 30-MHz longitudinal and 10-MHz shear waves propagating along the [100] direction showed that the excess attenuation at T<TC passes through a maximum near 60°K and is small at 4 2°K. An external magnetic field H≳5 kG removed the excess attenuation at T<TC. No attenuation peak was found at TC. The excess attenuation at T<TC is tentatively interpreted as being due to ferromagnetic domains. The elastic constants at 78°K are (in 1011 cgs units) c11 = 19.2±0.6, c44 = 5.42±0.13, c12 = 4.25±0.85. These lead to an adiabatic bulk modulus B = (9.2±0.6) ×1011 cgs units, and a Debye temperature θ = 350°K. © 1969 The American Institute of Physics.