Spin Excitation And Spin Polarization Study Of Magnetic Molecules And Magnetic Nanostructures On Metal Surfaces

In this thesis,using a low temperature ultra-high vacuum scanning tunneling microscopy(STM),equipped with high field superconducting magnet(Unisoku super-low temperature 1300S-~3He STM),we mainly studied the spin exchange interaction,the excitation of anisotropy state of spins,and their competition in the system of magnetic molecules and/or atoms on metal surfaces.In chapter 1,I introduce the background and the motivation of my work.It includes the detection and its principle of spin excitation states using STM,recent progresses using the high magnetic field STM on the studies of magnetic nanostructures.Some physical concepts relating to my works are introduced.In chapter 2,I study the spin excitation states.The spin excitation states can be from the exchange interaction of magnetic Phthalocyanine(Pc)molecules,and the strong magnetic anisotropy on metal surfaces.We use a monolayer of CoPc molecules as a buffer layer,and then grow another two molecule layers forming multilayered structures:FePc/CoPc/CoPc/Pb in sample#1 and FePc/FePc/CoPc/Pb in sample#2.The difference between these two samples is in the second layer,either with CoPc(in sample#1)or with FePc(in sample#2).A CoPc molecule has S =1/2 in sample-1,and a FePc molecule has S =1.We find that in these systems,co-existence of the spin exchange interaction and the strong magnetic anisotropy may lead to different excitation states,reflecting their competition in the multilayered molecular system.In our measurement,the magnetic anisotropy energy and the spin exchange interaction energy have been derived.In chapter 3,I present a comparative study for the lifetime of spin excited state on different metal surfaces.By preparing multilayer of CoPc molecules on Au(111)and Pb(111)surface,we mainly study the spin exchange interaction between CoPc molecules grown on different metal surface.The FWHM of the spin excitation peaks are obviously different,which reflects the different lifetimes of the spin excited states.It can be attributed to the different density of states on the Au and Pb surfaces,which may cause different scattering strength for the localized d electrons(in the Co ion of CoPc)by the s electrons in the metal substrates.In chapter 4,using spin-polarized tips coated by Fe and Cr,I investigate the magnetic cobalt islands on Pt(111)and Cu(111)surface respectively.Spin-resolved dI/dV spectroscopy,dI/dV mapping,and the magnetic switching of Fe-coated tips and cobalt islands by the applied magnetic field are observed.It is found that the Fe-coated tip can be used to detect the polarization of Co islands.