Lectures 19&20 (Magnetoresistance and Spin-Transfer Torque) Flashcards
What were read/write heads on hard disks replaced with?
Magnetic pole pieces to write and induction to read back data. Read part of head was replaced with MR sensor
Why did read part of read/write heads need replacing?
As data bits shrank, the stray field got harder to read and disk had to rotate faster to obtain readback signal
In an anisotropic field sensor, is current parallel or perpendicular to M larger resistance?
Current parallel = larger resistance
Why does current parallel to magnetisation have larger anisotropic MR?
The scattering is more effective when the current is normal to the plane of the electron orbits
In spin-dependent transport, what is the Mott model and why can it be used?
Mott 2-current model treats spin up and down conduction channels as independent
Since spin-flip scattering is very rare (100:1) in comparison to normal scattering
How will a current become spin polarised?
s-electrons (highly conducting) are scattered into available d-states
In exchange bias, how to the spins at the surface couple?
Via exchange
What effect does exchange bias have on the hysteresis loop? Why?
Shifts it left due to needing to overcome an extra energy barrier (exchange field) to reverse the magnetisation from exchange coupling between FM and AFM
In tunnel MR, what is conductance proportional to?
No. electrons available to tunnel from one FM layer and the number of empty states available in the other
What is P value for a large TMR?
~1
How does spin-transfer torque work?
Current polarised by spin-dependent scattering in an FM layer
If this current passes into a second FM in which M is not aligned with the first, the transverse component of the spin current is absorbed - this leads to dl/dt and so a torque on M
