1. P2-D125
Decrement of the Exchange Stiffness Constant of CoFeB thin films with Ar gas pressure.
Jaehun Cho, Jinyong Jung, Ka-Eon Kim, Sukmock Lee Chun-Yeol You*
Department of Physics, Inha University, Incheon , Korea
Introduction
Sample preparation
Motivation Si
CoFeB ( 25 nm )
SiO2 ( 50 nm )
Ta ( 5 nm )
Exchange stiffness constant is related by the number of nearest neighbor atoms and Curie Temperature.
Exchange stiffness constant - important parameter in the theory of micromagnetics
Determine the exchange stiffness constants - Inelastic neutron scattering experiments, spin wave resonance experiments, Brillouin light scattering (BLS)
Magnetron sputtering deposition
Base pressure : 2 × 10-9 Torr
Sputtering power: 100 W
Ar pressure : 1.5, 4.5, 7.5 and 10 mTorr
Substrate : Si (100)
Sample size : 10 mm(hor.) × 10 mm
Purpose
A few researches for exchange stiffness constant in CoFeB system*
Recently it is predicted that the critical current density depends on the exchange stiffness constant**.
Investigate the dependence of the exchange stiffness constant on the Ar gas pressure using BLS
Experimental results
* C. Bilzer et al. JAP 100, (2006)
** C. -Y. You, unpublished
Theory d B0 S B1 B2
Hysteresis loops for Co40Fe40B20 samples (left)
Resonance frequency (right) as a function of magnetic field for 1.5 mTorr Co40Fe40B20 film by BLS measurement. Black open circles and Red circles are surface mode and 1st bulk mode respectively. The solid lines are fitting and the open circles are experimental results.
P. Grunberg et al. JMMM 28, 319 (1982)
The BLS frequencies of the surface (DE) and bulk spin waves mode are analyzed using the eq. (1) and (2) respectively.
Experimental set up and Resonance frequency spectra
H = 2.81ⅹ105 A/m
XPS depth profile (left) for the sample with 1.5 mTorr CoFeB.
Average percent of atoms (right) in the CoFeB layer each Ar gas pressure.
4.5 mTorr is the highest average percent of Co and Fe atoms, will give high Curie temperature.
H = 1.71ⅹ105 A/m
ω, q
ωL, qL
qL±q
Spin wave
Scattered Photon
Incident Photon
ωL± ω
The magnetic properties were measured by a BLS with an in-plain wave number q//=1.727 X 10-5 cm-1 with the angle of incident as 45° (left).
BLS spectra (right) taken from the 25-nm-thick Co40Fe40B20 sample for different values of the applied magnetic field.
Brillouin spectra taken an incident angle of 45O for the inplane wave vector. The letter S indicates the surface and B1 for the 1st bulk mode.
Plots of measured values of Ms, A versus Ar gas pressure.
Co90Fe10 thin film has ⅹ105 A/m and 2.98 ⅹ10-11 J/m for Ms and A respectively
Ms and A are related with the Curie temperature
Summary
We have studied the fundamental magnetic properties of Co40Fe40B20 thin films, saturated magnetization Ms and exchange stiffness constant A by employing BLS.
The Ms decrease to 9.39 ⅹ105 A/m, the A decrease from 1.41 to 0.98 ⅹ10-11 J/m.
It will be need to study for the relation of exchange stiffness constants and Curie temperature.
Spintronics
Laboratory
April 25-27, KPS 2012 Spring Meeting