Tailoring the morphology and magnetic properties of Co film on ion-beam induced highly ordered Ge-substrate

Tailoring the morphology and magnetic properties of Co film on ion-beam induced highly ordered Ge-substrate

1. Tailoring the morphology and magnetic properties of Co film on ion-beam induced highly ordered Ge -substrate Indian Association for the Cultivation of Science Outline Collaborators Dr. Ranveer Singh, Incheon Dr. Biswarup Satpati Prof. Satyaranjan Bhattacharyya Prof. Tapobrata Som , IOP Introduction Experimental Scheme Ion beam induced patterning Magnetic properties Magnetic anisotropy: MOKE Spin reorientation: MFM Conclusions

2. Magnetoresistive (MR) sensors   From hard disk drives to space exploration to biomedicine and diagnostics: two goals: to detect an object or determine its position in space Introduction Three kinds of MR sensors are most frequently used by design engineers: - Anisotropic magnetoresistive effect (AMR) - Giant magnetoresistive effect (GMR) - Tunnel magnetoresistive effect (TMR) Biosensing

3. ( c), (d) bilayered Py film/Co line array structure before and after the adding of the magnetic cells ( c), (d) bilayered Py film/Co line array structure before and after the adding of the magnetic cells. Patterned by e-beam lithography Motivation in biosensors (a), (b) single-layered Co line array structure before and after the adding of the magnetic cells (a), (b) single-layered Co line array structure before and after the adding of the magnetic cells Switching fields of patterned structure with magnetic cells are significantly increased compared to the case without cells in the hard axis of the external field applied Journal of Applied Physics 111 , 07E506 (2012 ), IEEE transactions on magnetics,49,4040 (2013)

4. Magnetization on patterned substrates: Introduction Tailoring of magnetization dynamics in ferromagnetic thin films I n-plane uniaxial magnetic anisotropy (UMA) induced by nanoscale patterned substrates Film grown on energetic nanoscale topographically anisotropic substrates Origin of uniaxial magnetic anisotropy is modification in the spin-orbit coupling, i.e. to the symmetry breaking at the nanoscale steps of the ripple slopes

5. Incident Laser Reflected Laser φ Surface normal Pattern orientation Experimental Scheme 60 Growth of Co- overlayer   Patterning on Ge substrate Pristine-Ge Patterned-Ge Patterned-Ge λ Δ Δ Patterned-Ge Cobalt Cobalt 26 keV Au ion RF magnetron sputtering: nominal thickness 60 nm

6. Ion beam induced patterning Besides removing material, surface erosion process gives rise to pronounced topographical evolution Bradley and . Harper, J. Vac. Sci. Technol. A (1988)

7. Bradley and Shipman, PRL, 2010, 145501 Ion beam induced patterning 5 μ m Height (nm)

8. Morphology of grown Co overlayer Mollick et al, JMMM, 498, 166198, (2020)

9. Structural properties

10. Magnetic properties: MOKE   Mollick et al, Nanotechnology 29 125302 (2018)

11. Applied field Applied field (a) (b) Magnetic properties: Growth angle dependence Mollick et al, JMMM, 498, 166198, (2020)

12. 60 nm Co film on Patterned- Ge 500 nm Co film on pristine- Ge Magnetic properties: Growth angle dependence Mollick et al, JMMM, 498, 166198, (2020)

13. 15 nm -25 ° 20 ° Morphology MFM Phase 1 μ m 1 μ m 1x10 18 ions cm -2 125 nm Morphology 1 μ m -25 ° 35 ° MFM Phase 1 μ m Spin reorientation: MFM 2 μ m Gauss -20 ° 30 ° 500 Gauss 2 μ m 15 ° 1000 Gauss 2 μ m -7 ° 10 ° 1500 Gauss 2 μ m -3 ° 5 ° -22 ° Hard axis Easy axis MFM under variable external magnetic field Easy axis Mollick et al, Nanotechnology 29 125302 (2018)

14. Spin reorientation: MFM 2 μ m 2 μ m -22 ° 35 ° -17 ° 30 ° 2 μ m -15 ° 25 ° 2 μ m -10 ° 12 ° Hard axis Gauss 500 Gauss 1000 Gauss 1500 Gauss

15. (a) -25 ° 20 ° 1 μ m -22 ° 35 ° -18 ° 40 ° -25 ° 30 ° 1 μ m 1 μ m 1 μ m (b) (c) (d) Co/Pristine-Ge Co-film grown at 0 ° Co-film grown at 30 ° Co-film grown at 70 ° Local magnetic properties: MFM Mollick et al, JMMM, 498, 166198, (2020)

16. Conclusions Coercive field decreases with increasing ion fluence , decrease is much faster in the direction of magnetic hard axis High aspect ratio of the patterns allows a thicker conformal growth of Co films and observation of a strong uniaxial magnetic anisotropy in the thicker films Complete magnetic spin reorientation takes place along magnetic easy axis Direct evidence on the magnetic spin reorientations With growth angle magnetic films softens on a patterned substrate  

17. Acknowdelgements Prof. Anirban Mitra, IIT Roorkee Mr. Alapan Datta , IOP, Bhubaneswar School of Physical Sciences, NISER, Bhubaneswar SERB - DST