Using magnetoresistance measurements at 4.2 K, the magnetic transitions of Fe/Gd multilayers have been studied. At low field and low temperature, this system is in an aligned state where all the Gd spins (or Fe spins) are in the field direction and all the Fe spins (or Gd spins) are antiparallel to the field because of the antiferromagnetic coupling of Gd and Fe spins. We show that a phase transition from a Gd-aligned state to a twisted state is a surface-induced transititon which occurs at low field when the outermost layer is iron. This surface effect extends relatively far in the sample (several thousands of angstroms). These results are in good agreement with theoretical studies.
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George et al. (1994) studied this question.