1. rr Enhancement of magneto-optical Kerr effect signal
by using MgO capping layer with anti-reflective coating
Hee-Kyeong Hwang
Department of Physics, Inha University, Republic of Korea
Motivation
(I) Numerical results
MgO (tMgO)
Ferro-magnet
Substrate
A ferromagnet materials such as Fe, Co, and CoFeB have been heavily investigated. Because they play an important roles in next generation semiconductor devices such as a spin transfer torque magnetic random access memory (STT-MRAM).
It is important to observe magnetic properties in a ferromagnet materials and need a high quality magnetic information from many kinds of measurement to get reliable results.
Magneto-Optical Kerr Effect(MOKE) is a quite nice tool which can easily observe magnetic properties in a thin film.
However, if MOKE signal is usually not large enough, it is difficult to determine the magnetic property. rr
We calculated the MgO capping layer thickness dependence with the Anti-reflective coating.
θK, εK, Q, and (ΔR/R) are the Kerr angles, ellipsometry, optical constant, the ratio between the change of the reflectivity due to the change of the magnetization, respectively.
The magnitude of the θK and εK are changed depending on the thickness of MgO.
Purpose
(II) Experimental result (MOKE)
Base pressure : 2.5 × 10-8 Torr
tMgO = 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 nm
In order to obtain spin signals more exactly and reliably in ferromagnetic thin film, the enhanced MOKE signal is required.
Optical anti-reflection (AR) layer can be a good solution. It is well-known that the MOKE signal improve with AR layer. Due to the multiple reflections, the incident beam has more chances to interact with the magnetic layer, which enhanced magneto-optical effect.
In this study, we investigate MOKE signal with additional MgO-AR coating layer.
(a)
(b)
Si/SiOx substrate
Ta (4 nm)
Pt (4 nm)
Co (2 nm)
MgO (tMgO nm)
Schematic system Anti-reflective coating
Anti-reflective coating is a type of optical coating applied to the surface of films and other optical elements to reduce reflection.
Due to the multiple reflections, the incident beam has more chances to interact with the magnetic layer, which enhanced magneto-optical effect.
We fabricate the sample which structure is SiOx(sub.)/Ta(4)/Pt(4)/Co(2)/MgO(tMgO)/Ta(4). (Fig. a).
Fig. b indicate the result of MOKE measurement depending on MgO capping thickness and the magnitude of MOKE signals are changed depending on the thickness of MgO.
Experimental methods
(a)
(b)
Fig. (a) The schematic of MOKE measurement.
MOKE can be further categorized by the direction of the magnetization vector with respect to the reflecting surface and the plane of incidence. 3 kinds of MOKE are shown in Fig. (b)
Magnetic media changes polarization of reflected light compared to incident light.
We found the changes of MOKE signal strength as a function of MgO layer thickness.
When we used the 10nm of MgO thickness, MOKE intensity have a maximum value respectively.
As MgO thickness increases, MOKE intensity tends to decrease.
Summary
We investigate an intensity of MOKE signal by using various MgO thickness capping layers in heavy metal/ferromagnet structure.
From the MgO thickness dependence measurement, we found that the intensity has a maximum value at the 10 nm MgO thickness.
Department of Physics, INHA University, Korea