Proximity effect induced enhanced spin pumping in Py/Gd at room temperature

We report on ferromagnetic resonance spectroscopy studies of Py/Gd system by varying thickness of Gd layer. We found that a portion of the Gd layer at the interface becomes ferromagnetically ordered at room temperature and become antiferromagnetic coupled to the Py due to the magnetic proximity effect, as evidenced by a Gd-thickness dependent shift in the resonance field and exchange bias field. We show a large increase in the effective Gilbert damping of the Py layer when the thickness of the adjacent Gd layer is increased. We argue that a major contribution of this increase is due to the spin pumping effect into the ordered ferromagnetic Gd layer.