Abstract
Heterostructures of Co-doped ZnO and Permalloy were investigated for their static and dynamic magnetic interactions. The highly Co-doped ZnO is paramagnetic at room temperature and becomes an uncompensated antiferromagnet at low temperatures, showing a narrowly opened hysteresis and a vertical exchange-bias shift even in the absence of any ferromagnetic layer. At low temperatures in combination with Permalloy, an exchange bias is found causing a horizontal as well as a vertical shift of the hysteresis of the heterostructure together with an increase in coercive field. Furthermore, an increase in the Gilbert damping parameter at room temperature was found by multifrequency ferromagnetic resonance (FMR), indicating spin pumping. Temperature dependent FMR shows a maximum in magnetic damping close to the magnetic phase transition. These measurements also evidence the exchange-bias interaction of Permalloy and long-range ordered Co–O–Co structures in ZnO, which are barely detectable by SQUID due to the shorter probing times in FMR.
Highlights
In spintronics, a variety of concepts have been developed over the past few years to generate and manipulate spin currents.[1,2]Among them are the spin Hall effect (SHE), which originates from the spin–orbit coupling,[3] spin caloritronics,[4] utilizing the spin Seebeck effect,[5] or spin-transfer torque due to angular momentum conservation[6] as examples
The static and dynamic magnetic coupling of Co:ZnO, which is weakly paramagnetic at room temperature and an uncompensated AFM at low temperatures, with ferromagnetic Py was investigated by means of superconducting quantum interference device (SQUID) magnetometry and ferromagnetic resonance (FMR)
The FMR measurements at room temperature reveal an increase in the Gilbert damping parameter for 50% Co:ZnO/Py and 60% Co:ZnO/Py, whereas 30% Co:ZnO/Py is in the range of an individual Py film
Summary
A variety of concepts have been developed over the past few years to generate and manipulate spin currents.[1,2]. Spin pumping,[7] where a precessing magnetization transfers angular momentum to an adjacent layer, proved to be a very versatile method since it has been reported for different types of magnetic orders[8,9,10,11] or electrical properties[12–14] of materials. It could be verified in trilayer systems where the precessing ferromagnet and the spin sink, into which the angular momentum is transferred, are separated by a nonmagnetic spacer.[15–18]. Heterostructures with an Al spacer were investigated to rule out intermixing at the interface as a source for the coupling effect
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