INVESTIGATION OF ACOUSTICAL PROPERTIES OF Cr

IN THE LOW TEMPERATURE REGION

P.P. Pal-Val, L.N. Pal-Val, Yu.A. Semerenko

B.Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, Kharkov, Ukraine

In the temperature range 5¸325 K the temperature dependences of decrement d and dynamic Young's modulus Е in a single crystal and polycrystalline Cr are investigated. The temperature spectra of d and Е are detailed investigated in the region of magnetic phase transitions T_SF»124 K and T_N»310 K.

Samples of two types were investigated: 1) single crystal with the residual resistivity ratio RRR=33; 2) polycrystalline sample with industrial purity.

Acoustic measurements were carried out by two methods: 1) flexural vibration technique at frequencies f ~4 kHz (fig.1.a); 2) two-component composite vibrator technique on longitudinal standing waves at frequencies f ~75 kHz, the ultrasonic strain amplitude were varied in the intervals 10^-8<e₀<10^-6 (fig.1.b). The RRR was determined by measuring the temperature dependence of the resistance of the samples in the interval 5-300 K using four-point method at two opposite directions of a transport current and then extrapolating the experimental data to 0 K. For all measurements, temperature was stabilized to <50 mK using a copper-constantan thermocouple and thermoresistive AsGa thermometer and resistive heater. The temperature changes rate during thermocyclings was ~ 1 K/min. The acoustic and resistivity measurements were carried out in absence of a magnetic field. The crystallographic orientation of the axis of the single crystal sample was determined with aid of the Laue diffraction pattern to an accuracy of ±1^o.

Fig. 1. Temperature dependence of the logarithmic decrement d and dynamic Young's modulus Е in a single crystal (a) and polycrystalline Cr (b).