Non-linear GMR in dual spin valves: Supplementary Information
Micromagnetic simulation of the dual spin valve structure:
Micromagnetic simulations of the dual spin valve structures used in the experiments have
been performed using 3D-Object oriented micromagnetic framework software (Oommf)†.
The figure below shows the plan view of magnetisation states of individual layers of
DSV(2,2) at different magnetic fields applied along the long axis. A bias field of 10mT is
applied to the top CoFe layer. For simulation, pillar structure is divided into unit cells of
size 10x10x2nm3. Saturation magnetisation, exchange coefficient and uniaxial anisotropy
of CoFe are set to 1.8  106 Am-1, 3  10-11 Jm-1 and -1.5  104 Jm-3 respectively. The
corresponding values for NiFe are 0.86  106 Am-1, 1.3 × 10-11 Jm-1and -3  103 Jm-3
respectively. The damping coefficient is set to 0.5, which allows rapid convergence.
Micromagnetic simulations were started from positive saturation at 150 mT in which all
layers are parallel (Point A in the figure). Once the magnetic field is decreased to about
70mT (Point B), the middle NiFe layer switches under the influence of the magnetostatic
interactions of the outer CoFe layers, which are parallel to each others. When the
magnetic field is reversed to about -30mT, the bottom CoFe layer switches (Point C). In
the minor loops repeated sweeping between points C and D results in the NiFe switching
back and forth, leaving outer CoFe layers magnetostatically-coupled antiparallel.
†
http://math.nist.gov/oommf. Version 1.2.a4 of the software was used.
The graph below shows the magnetic moment of unpatterned thin film material showing
the NiFe layer as a function of NiFe layer thickness. It shows that there is possibly a
dead layer but it is less than 0.5 nm.