Abstract
The phase boundaries of the magnetic phase diagram of chromium near the spin-flip temperature are mapped out (a) by experimentally observing the peaks in the ultrasonic attenuation which occur at these boundaries, and (b) by theoretically analysing a model free energy. The phase diagram has a critical point and a triple point and reasonable qualitative agreement between theory and experiment is found. A mean field theory of a number of singular observable properties near the critical point is presented. Also the magnetic field dependence of the Neel temperature is determined up to 16T, possible ultrasonic-induced Q switching is reported, and a frequency-dependent spike in the attenuation is described.