Rotation of the Pinning Direction in NiFe/FeMn bilayersX. P. Qiu , S. M. Zhou
Department of Physics, Fudan University, Shanghai 200433, China
FM
AFM
Exchange Bias (EB)
Training Effect
-300 -200 -100 0 100
Magnetic Field (G)
Mom
ent (
arb.
uni
ts)
1st 2nd 20th
0 5 10 15 20
40
50
60
HC
HE
Cycle number n
HE(n
), H
C (
n)
(Oe)
HC and HE decrease during consecutive sweep of hysteresis loops.
Recovery Effect
Steven Berems et al., PRL 95, 157202 (2005)
Hysteretic Behavior of EB
Angular dependence of exchange bias shows hysteresis between clockwise and counterclockwise rotaions.
mx
my
H=00 90 180 270
-1
0
1
my
Mo
men
t (a
rb.
un
its)
Rtn
(deg)
mxPD
Method to Identify the Pinning Direction (PD)
By rotating the sample in the film plane under zero magnetic field, the PD can be easily identified from the angular dependence of its magnetic moment.
0 180 360-1
0
1
-400 -200 0 200-1
0
1
1st 20th
1st 20th
Magnetic field (Oe)
mx (
arb.
uni
ts)
(b)
my (
arb.
uni
ts)
Rtn
(deg)
(a)
Correlation between Training effect and the Rotated Pinning Direction
40
50
60
0 5 10 15 200
5
10
15
20
HC
HE
HE(n
), H
C (
n) (
Oe)
(d)
(c)
Cycle number n
PD(n
) (d
eg)
Rotation of PD successfully explain the decrease of HC and HE in training effect of EB.
-60 -30 0 30 6015
30
45
-20
0
20
H-Loop
(deg)
HC (
Oe)
CCW CW
PD (
deg)
-180 0 1805
10
0
180
CCW CW
HC (
Oe)
H-Loop
(deg)
ED (
deg)
FeNi single layer FeNi/FeMn bilayer
ED only 00 or 1800 PD oscillates around 00
Origin of the hysteretic behavior of EB
0 -30 -60 -900
10
20
3010
20
30
40
50
PD
(de
g)
(b)
H-Loop
(deg)
H
E(C
)/HE
(C)(n
=1)
(%
)
HE
HC
(a)
0
20
40
60
0 1 2 3 4 5 60
10
20
30
HE
HC
(c)
(d)
tAFM
(nm)
Dependence of ΔθPD on θH-Loop and tAFM
Asymmetric Recovery EffectAfter training measurements, a magnetic field is applied at 900or -900
(with respect to the initial PD) to recover the EB.
900 -900
900≠ -900!
Schematic Explanation
Initial PD
Rotated PD
HRE
Spontaneous Recovery of PD
0 24 48 72 960
5
10
15
20
HInitial PD
Rotated PD
PD (
deg)
Waiting Time (hours)
ConclusionPinning direction is identified and can be used to successfully explain the training effect, hysteretic behavior of angular dependence and recovery effect of exchange bias. Pinning direction is an important physical quantity in exchange bias.
Reference:(1). Steven Brems, Dieter Buntinx, KristiaanTemst, Chris Van Haesendonck, Florin Raduand HartmutZabelPhys. Rev. Lett. 95, 157202 (2005)(1). T. R. Gao, D. Z. Yang, and S. M. Zhou, R. Chantrell, P. Asselin, J. Du, X. S. WuPhys. Rev. Lett. 99, 057201 (2007) (2). X. P. Qiu, D. Z. Yang, S. M. Zhou, R. Chantrell, K. O’ Grady, U. Nowak, J. Du, X. J. Bai, and L. SunPhys. Rev. Lett. 101, 147207 (2008)(3). X. P. Qiu, Z. Shi, S. M. Zhou , J. Du, X. J. Bai, R. Chantrell and L. Sun J.Appl. Phys, 106, 063903 (2009)