  We investigate unnatural-parity high-spin states in neutron-rich Cr and Fe
isotopes using large-scale shell-model calculations. These shell-model
calculations are carried out within the model space of $fp$-shell + $0g_{9/2}$
+ $1d_{5/2}$ orbits with the truncation allowing $1\hbar\omega$ excitation of a
neutron. The effective Hamiltonian consists of GXPF1Br for $fp$-shell orbits
and $V_{\rm MU}$ with a modification for the other parts. The present
shell-model calculations can describe and predict the energy levels of both
natural- and unnatural-parity states up to the high-spin states in Cr and Fe
isotopes with $N\le35$. The total energy surfaces present the prolate
deformations on the whole and indicate that the excitation of one neutron into
the $0g_{9/2}$ orbit plays the role of enhancing the prolate deformation. For
the positive(unnatural)-parity states in odd-mass Cr and Fe isotopes, their
energy levels and prolate deformations indicate the decoupling limit of the
particle-plus-rotor model. The sharp drop of the $9/2_{1}^{+}$ levels in going
from $N=29$ to $N=35$ in odd-mass Cr and Fe isotopes is explained by the Fermi
surface approaching the $\nu 0g_{9/2}$ orbit.
