Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

Titile: Study of switching field statistics of Permalloy (Ni 80 Fe 20 ) Hall bars by planar Hall effect
Author: Arnab Roy
Planar Hall effect was used to study the switching behaviour of 1mm*100µm*15nm permalloy
(Ni 80 Fe 20 ) Hall bars grown in (111) orientation on Si(100). Reversal model was Arrhenius type
activation over energy barriers,
−∆E
( H )
kBT
. Statistical analyis of the field-driven magnetization
p(
H ) = e
reversal process was carried out by studying the switching field for a large number of magnetic field
cycles beween ±20Oe. A potrtion of a few typical hysteresis curves is shown in figure 1.
⎛ H ⎞
The model proposed by M.P.Sharrock[1] : ∆ E( H ) = KV
⎜1
−
H
⎟ with H O =2xK/M was used to find
⎝ 0 ⎠
the shape of the energy landscape for the bar undergoing reversal in an applied field. Multiple
reversal paths were observed for a given wire under the same conditions(figure 2), each distribution
in very good agreement with the above model, allowing the calculation of :
1. Temperature dependence of the effective anisotropy constant for the bar; K(T)= (1/2)*H o M(T)
(x=1 for applied field at 0 O )
2. Energy barrier landscape: An exponent m= 1.5 to 2 is expected to leading order in the expansion
of the energy barrier according to the Stoner Wolfarth model, however, our results give an exponent
of 2.8 to 3 for all angles (out of plane) of the applied field for the principal reversal path, pointing to
mechanisms other than coherent rotation at work. If domain wall propagation and pinning is the
mechanism of reversal, this study determines the energy landscape around the pinning field.
m
-2.0x10 -5
120
-2.5x10 -5
100
Hall voltage (V)
-3.0x10 -5
No. of Reversals
80
60
40
-3.5x10 -5
20
0
-4.0x10 -5
3 4 5 6 7
H(Oe)
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
H(Oe)
Figure 1. Figure 2.
References:
[1] M.P.Sharrock, J. Appl. Phys. 76, 6413 (1994);