  Optical orientation of carrier spins by circularly polarized light is the
basic concept and tool of spin physics in semiconductors. We study the optical
orientation of electrons and holes in a crystal of the
FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$ lead halide perovskite by means of
polarized photoluminescence, time-resolved differential reflectivity, and
time-resolved Kerr rotation. At the cryogenic temperature of 1.6 K the optical
orientation degree measured for continuous-wave excitaton reaches 6% for
localized electrons and 2\% for localized holes. Their contributions are
distinguished from each other and from exciton optical orientation through the
pronounced Hanle effect in transverse magnetic fields and the polarization
recovery effect in longitudinal magnetic fields. The optical orientation degree
is highly stable against detuning of the laser photon energy from the band gap
by up to 0.25 eV, showing then a gradual decrease for detunings up to 0.9 eV.
This evidences the inefficiency of spin relaxation mechanisms for free carriers
during their energy relaxation. Spin relaxation for localized electrons and
holes is provided by the hyperfine interaction with the nuclear spins. Dynamic
polarization of nuclear spins is demonstrated by the Overhauser field reaching
4 mT acting on the electrons and $-76$ mT acting on the holes. This confirms
the specifics of lead halide perovskite semiconductors, where the hole
hyperfine interaction with the nuclei considerably exceeds that of the
electron.
