Influence of the phase transition of Tb on the magnetic properties of Fe/Tb multilayers

The impact of the phase transition between para- and ferromagnetic states of Tb on the magnetic properties of Fe/Tb multilayers has been studied by taking low temperature Mossbauer measurements. 26 Fe/Tb multilayer samples with a wide range of thickness were fabricated by planar magnetron sputtering on polyester and glass substrates. The magnetic and structural properties of these samples were examined using x-ray diffraction, Mossbauer spectroscopy, and torque magnetometry. At room temperature, Mossbauer spectra show perpendicular magnetic anisotropy (PMA) of the Fe magnetic moments for samples that consist of Fe layers and mixed interfaces only. The formation of an unmixed Tb layer starting at about 12 Angstrom Tb layer thickness leads to parallel alignment of the Fe magnetic moments. For samples for which discrete Tb layers are formed, these Tb layers are probably paramagnetic at room temperature as can be deduced from low temperature Mossbauer measurements and room temperature torque measurement. The hyperfine field of Fe in these multilayers as determined from Mossbauer spectroscopy shows a relative minimum around the Curie temperature of Tb of 220 K indicating reorientation of the Fe moments due to spin polarization of Tb. (C) 1999 American Institute of Physics. [S0021-8979(99)46008-6].