  The weak itinerant ferromagnet UIr is studied by magnetization and
magnetostriction measurements. Critical behavior, which surprisingly extends up
to several Tesla, is observed at the Curie temperature $T_C\simeq45$ K and is
analyzed using Arrott and Maxwell relations. Critical exponents are found that
do not match with any of the well-known universality classes. The
low-temperature magnetization $M_s\simeq0.5$ $\mu_B \cong const.$ below 3 T
rises towards higher fields and converges asymptotically around 50 T with the
magnetization at $T_C$. From the magnetostriction and magnetization data, we
extract the uniaxial pressure dependences of $T_C$, using a new method
presented here, and of $M_s$. These results should serve as a basis for
understanding spin fluctuations in anisotropic itinerant ferromagnets.
