Spin Valve Systems for Angle Sensor Applications - tuprints

2.5 Spin Valve System 15
MR (%)
8
7
6
5
4
3
2
1
0
FL
PL
H c2
H eb
-125 -100 -75 -50 -25 0 25
µ H(mT)
0
Figure 2.12: Major loop of an MR curve measured from a spin valve.
After the field direction switches to a negative polarity, the magnetization of the free layer
reverses direction, while the magnetization of the pinned layer remains fixed. The resistance
now rises to the maximum value, because the magnetization of the free and reference layers
are now in the anti-parallel state. Only upon application of a field greater than the exchange
bias field Heb does the magnetization of the pinned layer rotate in the direction of the applied
field. The measured MR drops to zero at this point. The Heb is determined at the halfway
point in the hysteresis of the major loop and at half the MR value as seen in Figure 2.12.
After the exchange bias effect is overcome by the applied field, the magnetization of the free
and pinned layers are again in the parallel orientation.
Numerous other magnetic parameters, such as the interlayer coupling between the free and
pinned layer He and coercivity of the free layer Hc1 and the pinned layer Hc2 can also be
extracted directly from an MR measurement. He is the shift in the minor loop of an MR or
magnetization curve from the zero field (see Figure 2.13). A positive shift is an indication of
ferromagnetic interlayer coupling and a negative shift of anti-ferromagnetic interlayer
coupling.
MR(%)
6
5
4
3
2
1
0
H e
H c1
-3 -2 -1 0 1 2 3
µ 0 H(mT)
Figure 2.13: Minor loop of an MR curve measured from a spin valve.
The coercivity is a measure of the uniaxial anisotropy of the ferromagnetic layer and is
represented by the hysteresis seen in the closed loop of the MR curve (see Figure 2.12). Hc1 is
measured from the half-way point of hysteresis in the minor loop of an MR curve and is