Influence of ferromagnetic layer thickness and blocking temperature in symmetric exchange bias spin valve systems
1
1,3
, U.D Chacon , J. Quispe-Marcatoma & E. Baggio-Saitovitch 1 2 3 CBPF- Brasil, SRMU-India and UNMSM-Peru
Exchange biased spin valves [1] have played important roles in the magnetoelectronic devices, for example, read heads for high-density magnetic recording, high sensitive magnetic field sensors and magnetic memory cells [2] Experimentally, exchange bias effect manifests itself in a field shift, Hex, of the hysteresis loop along the field axis, typically accompanied by an increase of the Coercivity. This is due to an interaction between the AF and F materials when cooled in applied magnetic fields field cooling, FC below the Néel temperature TN of the AF layer
FM thickness (20 nm) 0,0008
Exchange bias field for Single pinned layer
100 K
0,0002 0,0000 -0,0002 -0,0004
FeMn (10 nm) NiFe (t)
The interfacial unidirectional energy density [3]
-0,0008
0,0004
0,0000
-400
-200
0
200
-0,0006
400 -300
-200
Magnetic Field (Oe)
-100
-400
0
-200
0
200
-0,0008 400
-400
-200
Magnetic Field (Oe)
Magnetic Field (Oe)
0
200
400
Magnetic Field (Oe)
FM thickness (30 nm) 0,0008 0,0006
0,0008
50K
0,0006
200 K 0,0004
0,0004
0,0004 M o m en t (em u )
M o m en t (em u )
0,0004
100 K
0,0002 0,0000 -0,0002 -0,0004 -0,0006
0,0002
M o m en t (em u )
Si (111)
0,0000 -0,0002 -0,0004
0
500
-0,0008 1000 1500 2000 -2000
Magnetic Field (O e)
0,0000
-0,0004
-0,0006
-0,0008 -2000 -1500 -1000 -500
-1000
0
1000
2000
Magnetic Field (O e)
ZFC and FC curve Magnetic moment for NiFe(0.75 μB) and for CoFe(2.4 μB)
When FM thickness increases, hysteresis loop behaviour reveals the shrinkage in coercive field and reduction in exchange bias
-0,0004
-800
-400
0
400
@ lower FM thickness and soft magnetic nature enhances the exchange bias And coercive field No training effect observed but coercivity trend changes
800
-600
Magnetic Field (O e)
0
600
Magnetic Field (Oe)
2646
10 nm
2647
2648
50 nm -800
The hitherto, puzzling role of FM thickness has been convincingly explained
0,0000
2650
CONCLUSION Substantial progress has been made in elucidating some qualitative details concerning the phenomenon of exchange anisotropy
300 K
FM thickness
Blocking temperature for FeMn 390-470 K
ACKNOWLEDGEMENTS
0,0000
-0,0004
Ru (5 nm)
Temperature dependance follows, this equation
0,0002
-0,0002
-0,0004
-0,0006
300 K
0,0006
0,0004
0,0004
Ru (5 nm)
200 K
M o m en t (em u )
CoFe (t)
50K
M o m en t (em u )
0,0006
0,0008
M o m en t (em u )
FeMn (10 nm)
RESULTS
M o m en t (em u )
Ru (5 nm)
The samples were grown over non-etched Si(111) substrates Deposition method: DC magnetron sequential sputtering ( 5 target) Base pressure Pb=5*10-8torr; working pressure Pt=2*10-3torr; Deposition rate: Ru= 1.02Å/s, NiFe=0.39Å/s,CoFe=0.82Å/s and FeMn=0.83Å/s. Si(111)/ Ru50Å/NiFe(t)/FeMn100Å/Ru50Å/ CoFe(t)/FeMn100Å/Ru50Å tFM={100, 200, 300, 400 and 500 Å} X-ray reflectivity measurement was used to measure the thickness. Polynomial function was used to calculate the deposition rate. Magnetization measurements - Cryofree Versalab, @ CBPF
Mo m ent (em u )
MAGNETIC MEASUREMENTS
1
EXPERIMENTAL
Introduction
Normalized magnetization (a.u)
K. Ashok
1,2
REFERENCES
-400
0
400
800
Magnetic Field (Oe)
[1]J.C.S.Kools, IEEE TRANSACTIONS ON MAGNETICS, 32 (1996) 3165; [2] S.H. Jang, T. Kang, H.J. Kim, K.Y Kim, JMMM 239 (2002) 179 [3]A.E. Berkowitz!, Kentaro Takano, JMMM 200 (1999) 552}570 [4] J. Nogue, Ivan K. Schuller, JMMM192 (1999) 203Ð232