  Phase transition and critical properties of Ising-like spin-orbital
interacting systems in 2-dimensional triangular lattice are investigated. We
first show that the ground state of the system is a composite spin-orbital
ferro-ordered phase. Though Landau effective field theory predicts the
second-order phase transition of the composite spin-orbital order, however, the
critical exponents obtained by the renormalization group approach demonstrate
that the spin-orbital order-disorder transition is far from the second-order,
rather, it is more close to the first-order, implying that the widely observed
first-order transition in many transition-metal oxides may be intrinsic. The
unusual critical behavior near the transition point is attributed to the
fractionalization of the composite order parameter.
