Interesting, page-5467

what about this ? Will this take over IBX research?

https://sites.brown.edu/xiaolab/what-is-spintronics/

Magnetic Tunneling Junctions (MTJs)

Another type of magnetoresistance that is governed by similar quantum mechanical laws is being exploited as a better mechanism for a much more sensitive magnetic field sensor. Like GMR, tunneling magnetoresistance (TMR) in a multilayer junction filters one spin polarization over another depending on the orientation of an external magnetic field. However, the two technologies differ in their exact filtering mechanism.

In a magnetic tunneling junction (MTJ), the device which employs the tunneling magnetoresistance effect, two magnetic layers are separated by a thin insulating layer. If a bias is placed across the junction, electrons will tunnel through depending on the relative orientation of the two ferromagnetic plates.

In a magnetized ferromagnet, the density of states (DoS) differs between up and down spins, causing the intrinsic magnetization of the material. Because of this, the magnet has more states available to one spin orientation than another. When a bias voltage is placed across the barrier, electrons will tunnel across depending on the availability of free states for its spin direction. Thus, if two magnetic layers are parallel, a majority of electrons in one will find many states of similar orientation in the other, causing a large current to tunnel through and a lowering of overall resistance. However, if they are antiparallel, both spin directions will encounter a bottleneck in either of the two plates, resulting in a higher total resistance.

TMR effect is larger than GMR effect by about a factor of 10. Currently, TMR MTJ sensors have been used in hard drives.

polarized electrons within a conductor is necessary. A phenomenon called the spin Hall effect may be the solution.

In the regular Hall effect, if a magnetic field is place d perpendicular to the direction of current flow in a conductor, a bias voltage will be created perpendicular to both across the conductor. The reason for this is the electrons in the current interact with the magnetic field and experience a Lorentz force at right angles to the field and direction of current flow. They are pushed to one side of the conductor, and an electric field is created across the conductor.

In the spin Hall effect, a similar phenomenon occurs. Because the spin of an electron is coupled to its magnetic moment, if an electric field is placed perpendicular to the direction of current flow, the electrons’ spin degree of freedom interacts with the field and also experiences a Lorentz force. However, since electron spin can point either up or down, the two types of electrons will separate and move to opposite sides of the conductor. Although it was predicted almost 40 years ago, the spin Hall effect has received significant interest within the past decade.

Magnetic (spin) transistors

In an ordinary transistor, specifically an n-p-n type transistor, two n-type semiconductors are separated by a p-type semiconductor. Near the n-p-n junction, a gate controls the voltage across the p-type semiconductor. When a voltage is placed across the p-type semiconductor, free electrons either are attracted towards the gate (base) or away from it, depending on the direction of the applied voltage. This lack or presence of gate electrons controls the flow of current between the two n-type semiconductors, allowing the transistor to occupy both on and off states.

The problem with electrically-based transistors is their volatility. When power is shut off, the electrons in the p-type semiconductor are no longer confined to a single region and diffuse throughout, destroying their previous on or off configuration. This is the reason why computers cannot be instantly turned on and off. However, a new type of transistor may change all of this.

In a magnetic transistor, magnetized ferromagnetic layers replace the role of n and p-type semiconductors. Much like in a spin-valve, substantial current can flow through parallel magnetized ferromagnetic layers. However, if, say, in a three layer structure, the middle layer is antiparallel to the two outside layers, the current flow would be quite restricted, resulting in a high overall resistance. If the two outside layers are pinned and the middle layer allowed to be switched by an external magnetic field, a magnetic transistor could be made, with on and off configurations depending on the orientation of the middle magnetized layer.

Magnetic (spin) transistors are good candidates for logic devices (spin-logic).