Fig. 4. Pressure dependences of ultrasonic properties of DTN.

a Relative change of the sound velocity Δv/v of the longitudinal acoustic mode as function of the magnetic field (zero-pressure data are taken from ref. 33 and were measured at 0.3 K). The data are offset for clarity. b Relative change of the sound velocity Δv/v of the longitudinal acoustic mode as function of temperature. The data are offset for clarity. The onset of magnetic order is marked by red arrows.