Semi-inclusive \Lambda  hyperon production has been studied in the HERMES experiment using the E_e=27.5 GeV polarized positron beam incident on polarized or unpolarized internal gas target. The multiplicity distribution over fractional \Lambda  energy z has been investigated and the fragmentation function D^{{\Lambda }}_u(z) has been extracted. The D^{{\Lambda }}_u(z) found by HERMES is well described with the help of the parametrization based on the experiments on \Lambda  production in high energy proton--proton collisions, but it is substantially smaller then that deduced from the e⁺e^- annihilation data. The distribution over \Lambda  transverse momentum squared p²_T has also been analyzed. The results show that at z>0.2 the p²_T distribution is dominated by the quark transverse motion in the fragmentation process. The longitudinal spin transfer from the beam to the \Lambda  has been measured. The systematic uncertainty of the spin transfer has been reduced by reversal of the beam polarization several times during the data taking period. The spin transfer coefficient is found to be S_{{\Lambda }}=0.04 \pm 0.08(stat) \pm 0.03(syst) at an average fractional energy of the produced \Lambda  hyperons of \langle z \rangle =0.45. The dependence of the longitudinal spin transfer on z is presented and compared with recent theoretical calculations.

PACS numbers: 13.60.Rj