mnp is represented by the change of the magnetoresistive ratio mr with and without the presence of the mnp fig4 a and 4 b show the mr change due to the mnp for different groove dimensions in fig4 a and 4 b the width of the groove is fixed at 100 nm and 200 nm respectively while the length of the groove varies from 100 nm to 700 nm as shown in fig4 a the signal is at the maximum when the groove length is 100 nm in this simulation the results indicate the strong stray fields from the free and pinned layers acting on the mnp and the strong interaction between mnp dipole field the free layer the signal then decreases rapidly to the minimum with 200 nm groove length and increases as the length increases suggesting a complex interaction between the stray fields mnp dipole field and free layer fig4 b shows a maximum signal 8 9 u00d7 10 u2212 5 with 100 nm groove length structure in this simulation the signal then decreases dramatically with 200 nm groove length and increases slowly with a longer groove structure in comparison for a groove structure with a length longer than 200 nm the simulated biosensor having a 200 nm width shows a more stable signal change than the simulated biosensor with a 100 nm width this may be due to the fact that there is less magnetic material left on the magnetic biosensor after formation.