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)