The effect of the chromium layer thickness on the magnetic state of an [Fe/Cr/Gd/Cr] n multilayer structure is studied. A series of Fe/Cr/Gd structures with Cr spacer thicknesses of 4-30 Å is studied by SQUID magnetometry and ferromagnetic resonance in the temperature range 4.2-300 K. The obtained experimental results are described in terms of an effective field model, which takes into account a biquadratic contribution to the interlayer coupling energy and a nonuniform magnetization distribution inside the gado linium layer (which was detected earlier). Depending on the magnetic field and temperature, the following types of magnetic ordering are identified at various chromium layer thicknesses: ferromagnetic, antiferro magnetic, and canted ordering. A comparison of the experimental and calculated curves allowed us to deter mine the dependence of the bilinear (J 1 ) and biquadratic (J 2 ) exchange constants on chromium layer thick ness t Cr . Weak oscillations at a period of about 18 Å are detected in the J 1 (t Cr ) dependence in the range 8-30 Å. The interlayer coupling oscillations in the system under study are assumed to be related to the RKKY exchange interaction mechanism via the conduction electrons of Cr.

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