STUDY OF MAGNETIC PROPERTIES AND INTERFACIAL SPIN DYNAMICS IN FERROMAGNETIC / NOBLE METAL MULTILAYER STRUCTURES

Abstract

This works covers the magnetic and interfacial dynamics properties of ferromagnetic, antiferromagnetic and nonmagnetic metal based heterostructures, a convincing potential for insulator based spintronic devices. Magnetic insulator based spintronics offers numerous applications in the field of electronics industry. In this sector, nanometre (nm) thick low damping materials are critically needed for fundamental studies like spin pumping and spintronics based device application such as narrow band filters, band-notch (stop) filters, band-pass filters, spin-torque nano-oscillators etc. Yttrium iron garnet (Y3Fe5O12, YIG) a well-known, best suitable candidate among the other ferromagnetic materials. High grade YIG films that are nanometre thick are desperately needed. This works reports experimental and theoretical studies on nanometre (nm) thick yttrium iron garnet (YIG) films. At first, demonstrated the feasibility for deposition of YIG thin film using pulsed laser deposition (PLD) system, single crystalline gadolinium gallium garnet (GGG) (111), substrate was used for the deposition of YIG thin film. Optimization of deposition parameters and annealing process for the achievement of high-quality thin films are examined in depth. The morphology of thin films was analyzed using the atomic force microscope, the structural properties were studied using X-ray diffraction technique and Raman spectroscopy. Magnetic properties of films were investigated using the physical properties measurement system (PPMS) equipped with vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) spectroscopy. Furthermore, looked in to the effect of deposition parameters in the design of reciprocal and non-reciprocal microwave devices, this work demonstrated theoretically as well as experimentally, to study theoretically used HFSS simulation to understand the reciprocal and non- reciprocal EM (Electromagnetic) wave propagation in the range of microwave frequency through different transmission line using YIG thin film as active element. Spin pumping effect carried out in YIG thin film through deposition of thin layer of Ph.D. Thesis (SAROJ KUMAR JHA) vii nonmagnetic metal (Ta) layer and magnetic (Ni) material over the YIG, by controlled oxidation of Ni to NiO, found the significant enhancement in linewidth and other damping parameters, spin mixing conductance and other parameters also calculated to understand the spin pumping efficiency of heterostructure. In the final section of thesis, deposited the series of heterostructures of ferromagnetic and noble metal using the PLD and DC/RF sputtering technique, fabricated the multilayer thin film of normal metal copper (Cu), platinum (Pt), and tungsten (W) over yttrium iron garnet (YIG). To study the spin pumping effect in nanometer thick YIG film, Series of five samples were deposited over YIG. YIG/Pt, YIG/Cu/Pt, YIG/Cu/W, YIG/Cu/Pt/W and YIG/Cu/W/Pt. Spin pumping across the interface has been analyzed using the ferromagnetic resonance (FMR) technique, shows the change in damping parameters in all the structures confirms the spin pumping across the samples from YIG. Our finding broadens the range of possible application of nanometer (nm)-thick yttrium iron garnet (YIG) epitaxial films and yttrium iron garnet (YIG) based multilayers in insulator based spintronics devices, magnonics, etc.