Exchange Springs in <inline-formula> <tex-math notation="LaTeX">${L} 1_{0}$ </tex-math></inline-formula>-FePt(110)/<inline-formula> <tex-math notation="LaTeX">${A}1$ </tex-math></inline-formula>-FePt Bilayer Films

Abstract

To investigate the effect of hard/soft exchange spring on magnetic properties, L10-FePt/A1-FePt bilayer films had been fabricated on MgO(110) substrates by using magnetron sputtering. The hard layer annealed at a moderate temperature of 500 o C showed an unseparated granular morphology with an almost full coverage, in spite of an incomplete A1→L10 transition. The c axis (easy axis) of L10-FePt preferred to align in plane rather than off plane. For a system of L10-FePt(10 nm)/A1-FePt(20 nm), the magnetization jumped abruptly at +1.4 kOe (= nucleation field of soft layer) and -7 kOe (= switching field of hard layer), respectively. However, a perfectly rectangle-like magnetization curve with a coercivity as high as ~10 kOe was observed for a system of L10-FePt(30 nm)/A1-FePt(20 nm). This indicates that the exchange length might be able to be affected by grain growth in an incompletely A1→L10 transited FePt film. According to experimental results, exchange length of the annealed FePt(30 nm) film should exceed 10 nm, which is much larger than that (5 nm) of ideal L10-FePt. These bilayer films are suitable for fabricating MFM tips to measure different magnetic objects.Index Terms-coervicity, exchange spring, L10-FePt/A1-FePt bilayer film, magnetization reversal.

Magneto-optical Kerr effect and nuclear resonant scattering study of uni-directional anisotropy in hard-soft magnetic bilayers

“…This is due to the fact that the SM layer thickness of all the bilayers is greater than δ of the HM layer [i.e., δ(FePt) % 5 nm]. 26 To explore the possibility of EB phenomena, the Kerr hysteresis loops are measured with the bottom HM layer in both the demagnetized and remanent states. The remanent state is achieved by subjecting the sample to a saturating magnetic field (H SAT ) and subsequent field reduced to zero, whereas the demagnetized state is achieved by applying an alternating field of decreasing amplitude.…”