Dy(48 Å)/Fe(40 Å) multilayers were investigated by 57Fe and 161Dy Mössbauer spectroscopy in zero external field between 4.2 and 300 K. The 57Fe spectra could be analyzed in terms of a pure bcc-Fe contribution and an intermixed interface contribution. The latter is assigned to an amorphous Dy1−xFex interface alloy with an estimated most-probable composition x≊0.78. The bcc-Fe phase shows a broad spin-reorientation transition from a preferentially in-plane-oriented Fe-spin direction near 300 K to a more out-of-plane-oriented spin texture at 4.3 K characterized by an average misalignment angle of ∼52° relative to the sample-plane normal. The value of the average 161Dy hyperfine field at 4.2 K (583.0 T) is slightly larger than the value of bulk Dy metal, but is smaller than those of Dy–Fe intermetallics. The average orientation of Dy moments which was found to be random at 4.2 K may be the reason for the misalignment of Fe magnetic moments at low temperature. The magnetic ordering temperatures of the Dy layers were determined by superconducting quantum interference device magnetometry to be TC=110±15 K and TN=200±20 K, the latter value being in agreement with that estimated from 161Dy spectra.
The magnetization reversal of multilayers {Tb/Fe/Ag}10(S1), {Fe/Tb/Ag}10(S2), and {Fe/Tb}10(S3) is measured at room and low temperatures using polar magneto-optical Kerr (MOKE) spectroscopy and SQUID magnetometry. The Ag blocking layers in S1 and S2 strongly suppress the perpendicular magnetic anisotropy (PMA) induced by the Fe/Tb interfaces, whereby the Fe-on-Tb interfaces give rise to much stronger PMA than the Tb-on-Fe ones. MOKE ellipticity in the near-infrared reveals an uncoupled soft-magnetic contribution in all samples, S1–S3. It is attributed to amorphous iron segregated within the bulk of the α-Fe layers and contributing to about 10% of their volume.
Iron-site selective 57 Fe-Mössbauer spectra in external fields perpendicular to the layers were measured along the magnetization-hysteresis loop in a hcp-Tb/bcc-Fe multilayer with out-of-plane magnetic orientation and large coercivity. In the multidomain region, two oppositely and out-of-plane magnetized domain states in the Fe layers are distinguished in the spectra. The Fe-spin direction was found to be at oblique angles with respect to the surface normal (and Bext direction), reminiscent of a cone state. Fe-spin rotation was directly observed along the hysteresis loop, and the bcc-Fe-specific magnetization loop was calculated from the Mössbauer results.
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