We present results from a detailed study of spin injection in thin II–VI wide band gap semiconductor heterostructures by magnetooptical spectroscopy. It is shown that efficient spin alignment can be achieved in a diluted magnetic semiconductor barrier (a layer of ZnMnSe or ZnMnSe/CdSe superlattice) as thin as . Rather efficient spin injection from such a thin spin aligner to a non-magnetic quantum well is demonstrated, even when the tunneling energy barrier is as thick as . The effect of spin relaxation process on spin injection is also closely examined.