The structures and magnetic properties of nanoscale Pt/Co/NiO multilayers

• Main Authors: Shan-Hui Chung, 鍾杉慧
• Other Authors: Ko-Wei Lin
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/96848343149947141408

碩士 === 國立中興大學 === 材料科學與工程學系所 === 97 === Exchange bias in [Pt/Co]/NiO multilayers were studied as a function of film different Co or Pt thickness [Pt/Co]4 layer repetition with a dual ion beam deposition technique and capped with 20 nm of NiO on a SiO2 substrate. And control the NiO‘s orientation by the ability to regulate the ion beam energy using the End-Hall voltage (VEH) of the ion gun. Different Co thickness affect strongly the interfacial spin orientation, and thus exchange bias behavior when in contact with AF NiO. We find that the exchange bias is influenced strongly by the top [Pt/Co] layer configuration (composite [CoPt-Pt] or superlattice [Pt/Co] structure) when in contact with the bottom NiO layer. Perpendicular magnetic anisotropy of Co/Pt multilayers appears as the thinnest & thick [Pt(3 nm)/Co(0.6,2 nm)]4/NiO multilayer exhibits out-of-plane exchange bias field, a perpendicular Hex ~ -88.3 and -101 Oe at 5K was measured. Out-of-plane exchange bias is due to the mixing unstable interlayer energy of Co/Pt. We also note that CoPt alloy with a perpendicular easy axis can observed in TEM and XRD analysis when the Co layers are the thinnest. Different ion-beam energy(VEH=70、80、100、150 V)was used to change the bottom layers’(NiO) structure in Co/Pt multilayers. Co/Pt multilayers change of easy axis (out-of-plane toward in-plane) due to NiO’s orientation ordering induced by various End-Hall voltages. The intermixing is much more likely to occur in Co-Pt multilayers as compared to the Co-Pd system, which was observed in XRD. The PMA in [Pt/Co]4/NiO systems prepared with VEH=70 V is driven mainly by the heat of mixing. Perpendicular exchange bias was enhanced in change Pt thickness [Pt/Co]4 /NiO multilayers. At 298 K， there is not out-of-plane Hex⊥ in the [Pt(X nm)/Co]4/NiO multilayers. This is actually due to superparamagnetism. At 5 K，the perpendicular exchange bias Hex^ no variation with increase Pt thicknesses.This behavior may be due to the Pt thickness in excess of the critical value.