Magnetic properties under pressure in novel spin-triplet superconductor UTe$_2$

LettersInternational audienceWe report the magnetic susceptibility and the magnetization under pressures up to 1.7 GPa above the critical pressure, P$_c$ ∼ 1.5 GPa, for H || a, b, and c-axes in the novel spin triplet superconductor UTe$_2$. The anisotropic magnetic susceptibility at low pressure with the easy magnetization a-axis changes to the quasi-isotropic behavior at high pressure, revealing a rapid suppression of the susceptibility for a-axis, and a gradual increase of the susceptibility for the b-axis. At 1.7 GPa above P$_c$, magnetic anomalies are detected at TMO ∼ 3 K and TWMO ∼ 10 K. The former anomaly corresponds to long-range magnetic order, most likely antiferromagnetism, while the latter shows a broad anomaly, which is probably due to the development of short range order. The unusual decrease and increase of the susceptibility below TWMO for $H$ || a and b-axes, respectively, indicate the complex magnetic properties at low temperatures above P$_c$. This is related to the interplay between multiple fluctuations dominated by antiferromagnetism, ferromagnetism, valence and Fermi surface instabilities