Materials for Femtospin Project Colin Forbes

Introduction Brief Overview of Key materials Material sequencing Overview of experimental results Future

Materials of interest GdFeCo ternary alloys with 20-25% Gd & Co = 10% Gd/(FeCo) multilayers –20-25% volume fraction of Gd FePt (5nm) /Co (5,10-20nm) bilayers FeRh FeTb –TbFe 2 and TbFe 3 ordered phases Elemental RE –GdFe 2 ordered phases

Material Sequencing 1.GdFeCo ternary alloy 2. Gd/(FeCo) multilayers 3. FePt (5nm) /Co (5,10-20nm) bilayers 4.= FeTb, FeTb 2, FeTb 3 4.= FeRh 4.= Gd & GdFe 2

Experimental Analysis

Ternary Alloy Depositions –GdFeCo Gd – % Fe – 60 – 75% 50nm Co – 10% SiO 2 wafers used as substrates Depositions done at ambient temperatures Samples sent to Seagate Ternary Alloy Samples SiO 2 Ta Gd x Fe 90-x Co 10 Ta 5nm 50nm 5nm Where x =

XRD Analysis Gd 20 Fe 70 Co 10 (50nm) No crystalline structure Amorphous surface

Heated VSM GdFeCo alloys

Heated VSM 20% Gd has perpendicular anisotropy at room temperature while 25% Gd has in plane anisotropy Magnetic properties change with temperature 25% Gd switches from in plane to perpendicular anisotropy at ≈300°C

Multilayers of Gd and Fe 90 Co 10 - (40nm) Volume factor of Gd was either 20 or 25% Single bilayer Double bilayer Quadruple bilayer Depositions at room temperature Samples sent to Seagate Gd/(FeCo) Multilayer Samples SiO 2 Ta Gd Fe 90 Co 10 Ta SiO 2 Ta Gd Fe 90 Co 10 Ta Gd Fe 90 Co 10 SiO 2 Ta Gd Fe 90 Co 10 Ta Gd Fe 90 Co 10 Gd Fe 90 Co 10 5nm 40nm 5nm Gd Fe 90 Co 10

BH Looper Analysis Ta(5nm)/[Gd(20%)/Fe 90 Co 10 ](40nm)/Ta(5n m) in Plane Ta(5nm)/[Gd(25%)/Fe 90 Co 10 ](40nm)/ Ta(5nm) in Plane

VSM Analysis of Gd/FeCo multilayers

Ta(5nm)/[Gd (4nm) FeCo (16nm) ] 2 (40nm)/Ta(5nm) in Plane Temp / °C Heated VSM Measurements Ta(5nm)/[Gd (5nm) FeCo (15nm) ] 2 (40nm)/Ta(5nm) in Plane

Decrease in both saturation & coercivity general trend Not what was expected – in plane to perpendicular anisotropy switching expected at compositional temp

Future Improve multilayer structures of Gd/(FeCo) –Vary Volume fraction –Magnetic Properties –Crystal structure –Temperature analysis Investigate FePt/Co –FePt (5nm) Co (5,10-20nm) bilayers FeRh FeTb, FeTb 2, FeTb 3 Gd & GdFe 2