  We study the critical behavior of dc magnetization in the uranium ferromagnet
URhSi around the paramagnetic to ferromagnetic phase transition at T_C~ 10 K
with a modified Arrott plot, a Kouvel-Fisher plot, the critical isotherm
analysis and the scaling analysis. URhSi is isostructural to uranium
ferromagnetic superconductors URhGe and UCoGe. The critical exponent beta for
the temperature dependence of the spontaneous magnetization below TC, gamma for
the magnetic susceptibility, and delta for the magnetic isotherm at T_C in
URhSi have been determined as beta = 0.300 +- 0.002, gamma = 1.00 +- 0.02, and
delta = 4.38 +- 0.04 by the scaling analysis and the critical isotherm
analysis. These critical exponents fulfill the Widom scaling law delta = 1+
gamma/beta. Magnetization has strong uniaxial magnetic anisotropy in the
ferromagnetic state of URhSi. However, the universality class of the
ferromagnetic transition does not belong to the 3D Ising system with
short-range exchange interactions between magnetic moments (beta = 0.325, gamma
= 1.241, and delta = 4.82). The obtained exponents in URhSi are similar to
those in the uranium ferromagnetic superconductors UGe_2 and URhGe, and uranium
ferromagnets UIr and U(Co_0.98Os_0.02)Al. We have previously reported the
unconventional critical behavior of magnetization in the uranium ferromagnetic
superconductors [N. Tateiwa et al. Phys. Rev. B 89, 064420 (2014)]. The
universality class of the ferromagnetic transition in URhSi may belong to the
same one in the uranium ferromagnetic superconductors and the uranium
ferromagnets. The unconventional critical behavior of the magnetization in the
uranium compounds cannot be understood with previous theoretical
interpretations of critical phenomena. The absence of the superconductivity in
URhSi is discussed from several viewpoints.
