Magnetic And Spin-dependent Transport Properties Of Co/Pt Multilayers

Co/Pt multilayers have been widely used in modern spintronics applications, as they are expected to provide technically promising magnetic and spin-dependent transport properties such as high perpendicular magnetic anisotropy, large magneto-optical Kerr effect and anomalous Hall effect. However the thermal stability of Co/Pt multilayers limits the integration of Co/Pt multilayer-based spintronics elements with CMOS. So, it is of great importance to improve their thermal stability. In traditional Co/Pt multilayer-based perpendicular magnetic anisotropy spin valves, metallic antiferromagnets are commonly employed to induce exchange bias, but the serious current shunting effect caused by the thick metallic antiferromagnets lowers the giant magnetoresistance ratio of the spin valves. To overcome this problem, two methods could be adopted. The first one is to employ insulting antiferromagnets and the second one is to fabricate pseudo spin valves which totally cancel the needs of antiferromagnets. Focusing on the problems mentioned above, this thesis systematically studies the magnetic and spin-dependent transport properties of Co/Pt multilayers.At first, the interaction between insulting antiferromagnet NiO and Co/Pt multilayers is explored. It is found that room-temperature exchange bias can be observed when NiO layer is deposited on top of Co/Pt multilayers. When NiO layer is located below Co/Pt multilayers, no exchange bias is detected but the magnetic anisotropy and coercivity of Co/Pt multilayers are greatly affected. With increasing thickness of NiO layer, the coercivity exhibits a nonmonotonic decay. This phenomenon provides new ways to control the coercivity of Co/Pt multilayers.The impact of Co layer thickness, Pt inner layer thickness, Pt seed layer thickness, periodic number and different seed layers on the magnetic properties and anomalous Hall effect of Co/Pt multilayers is also investigated. The variations of relevant properties with the factors mentioned above is summarized and interpreted. This is of great reference value for the practical use of Co/Pt multilayer-based anomalous Hall effect elements.In this thesis, Co/Pt multilayer-based pseudo spin valves exhibiting perpendicular magnetic anisotropy have been prepared to reduce the current shunting effect caused by metallic antiferromagnets. At first, magnetization measurements of the Co/Pt multilayers are performed to select the reference and free layers. The selection criteria are square magnetic hysteresis loops, weaker current shunting effect and proper coercivity. Cu and Au layers are employed as spacer layers in the pseudo spin valves, respectively. The resulting pseudo spin valves exhibit two well separated hysteresis loops when the magnetic field is applied perpendicular to the film plane indicating good perpendicular magnetic anisotropy. The giant magnetoresistance ratio of the pseudo spin valves are higher than that of exchange-biased spin valves. The Cu spacer layer-based pseudo spin valve shows higher giant magnetoresistance ratio than that of Au spacer layer-based pseudo spin valve.As a key, the impact of Au spacer layers on the magnetic properties and anomalous Hall effect of Co/Pt multilayers is investigated. The Au spacer layers are inserted at the top of Co layers, namely Co-Pt interfaces. It is found that after the introduction of Au spacer layers, the perpendicular magnetic anisotropy, saturation magnetization, coercity and anomalous Hall effect of the Co/Pt multilayers are all enhanced in different degrees. Meanwhile, the multilayers’ resistance to thermal annealing is also improved. This is of great interest for the integration of Co/Pt multilayers with CMOS and its wider application in spintronics elements.