Low-frequency response in the magnetic susceptibility of antiferromagnetically coupled Fe/Cr multilayers

The magnetic field and temperature dependence of the low-frequency ( f<10 ⁴ Hz) in- and out-of-phase magnetic response of antiferromagnetically coupled Fe/Cr(1 0 0) shows that at T>100 K both the real ( χ') and imaginary ( χ″) parts of the susceptibility exhibit hysteretic dependence on the magnetic field with maxima of χ″( H) at H≈±25 Oe. At T=2 K the losses exhibit an unusual strong frequency dependence describable within a single relaxation time scheme. The corresponding relaxation time proves to be strongly field-dependent which could be related to some quantum tunneling processes at low temperatures.