Interface induced magnetic properties of thin films

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The rapid increase in magnetic memory storage density over the last three decades has been made possible by the discovery of interface-induced phenomena in ferromagnetic (FM)|non-magnetic (NM) multilayers. The discovery of giant magnetoresistance and tunnel magnetoresistance phenomena enabled the detection of magnetic moment direction and are key for the design of magnetic sensors that are responsible for >100 times increase in the recording density of hard drives. The observation of spin transfer torque (STT) and spin orbit torque, utilized to manipulate the magnetic moment direction, allows for a novel design of solid state non-volatile magnetic memories, which are identified as the next generation in memory devices. Another interface effect that has been intensively studied is the interlayer exchange coupling. This phenomenon has not been used to its full potential until now, since traditional coupling layers only allow for collinear orientation of magnetic moments of FM layers. Recently, we discovered and patented new coupling layer (CL) materials, which can be inserted instead of NM, between two ferromagnetic layers to precisely control the relative orientation of the magnetic moments of FM layers in FM|CL|FM. These new coupling layers have the potential to be used in the majority of magnetic nanodevices since the optimal design of magnetic nanodevices almost always requires non-collinear alignment between at least two neighboring ferromagnetic layers. This proposal focuses on understanding the origin of non-collinear coupling in FM|CL|FM structures and how to incorporate these structures into magnetic nanodevices. The emphasis will be on devices, which could benefit most from non-collinear alignment of magnetic moments, spin transfer torque magnetic random-access memories (STT MRAM), and nano-oscillators. STT MRAM with non-collinear alignment of magnetic moments are expected to have much faster write speeds and significantly low power consumption than the current state-of-the-art STT MRAM devices. Canada will benefit from significant intellectual property that has already been and will be generated, which could create an opportunity for HQP to develop these nanodevices in Canada. In addition to studying static effects, such as interlayer coupling, we will also study magnetization dynamic effects, spin pumping at FM|NM interfaces, and the subsequent transport of pure spin current in NM. Of specific interest are NM = Pt and Pd since they exhibit proximity magnetization when interfaced with ferromagnetic films. Pt and Pd also strongly affect magnetic static and dynamic properties of ferromagnetic layers, which can be beneficial like increase of surface anisotropy or detrimental like increase of magnetic damping. We will study the mechanisms responsible for increase of damping of ferromagnetic layers adjacent to Pt and Pd by means of spin pumping and inverse spin Hall effect.