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제목: Revealing magnetism of nanoislands with quantitative insights into spin-polarized scanning tunneling spectroscopy

연사: 박   수   현  박사님 (Max-Planck-Institut für Mikrostrukturphysik, Germany)
 

일시: 2013. 11. 11(월) 오후 4:00

장소: 제1과학관 3층 물리학과세미나실 31355호실

초록: The spin-dependent electronic structure1 and magnetization reversal2 of individual nanostructures have been successfully characterized by spin-polarized scanning tunneling microscopy/spectroscopy (SP-STM/S). In this talk, we present an application of SP-STM/S for a quantitative characterization of the magnetic properties3 of the tip used as a probe in SP-STM and for the investigation of the spin-dependent electronic structure in bilayer high Fe nanoislands.
We observe a superparamagnetic response of Fe-coated W tips. A temperature-dependent change of the spectroscopy signal, measured on biatomic-layer-high Co nanoislands on Cu(111)1,2 in magnetic fields oriented along the sample normal, shows a reduced slope around zero field of the field-dependent differential conductance for an increased temperature (Fig. 1). A quantitative analysis of the field- and temperature-dependent differential conductance data in the framework of superparamagnetism suggests that a magnetically isolated Fe nano-apex of a few hundreds Fe atoms determines the magnetic response of the tip.3
We also apply SP-STM/S to elucidate the magnetic state of a bilayer Fe islands on Cu(111), where the second layer Fe atoms are positioned at bridge sites of the underlying first Fe layer4. SP-STM/S reveals a magnetic contrast of a stripe pattern with a period of 1.28 nm, as shown in Fig. 2. Our detailed analysis of the magnetic-field-dependent stripe contrast with the characterization of the tip magnetization states clearly indicates that a non-collinear periodic spin-ordering is responsible for the stripe pattern. The electronic origin of this non-collinear spin-state is discussed.