Spintronics! Adding another dimension to the existing technology
sohini.bits
samontoy
Spintronics,
For those interested a little bit more on spintronics, I’ll shed some light on some of the things discussed in this paper.
Personally one of the most surprising facts about this article is the year it was published and the advances and problems faced at that time. In the year 2000, I was still in elementary school and I recall a boom in density storage media that became available computer hard drives. This boom was the result of incorporating a Giant Magnetoresistance (GMR) sensor into the read head. This allowed hard drives to decrease the amount of magnetic grains to write a single bit of information, from conventional Anisotropic Magnetoresistance (AMR) sensors which created an increase in density storage in the 90’s. It’s interesting that although Giant Magnetoresistance (GMR) had been discovered in the late 80’s it took slightly more than a decade to incorporate this effect into a consumer product. The reason is because you need to optimize a read with the magnetic media to obtain the best memory density.
The figure describing the GMR effect does explain how the effect occurs, but fails to really explain what is going on. Say you apply a magnetic field, both layers of the device will generally switch. Usually you use a structure that has its layers anti-ferromagnetically coupled, that is, both layers have their magnetization pointing opposite to each other, i.e. for example Co\Cu\Co. In addition, you pin one of the layers by using another stack of other magnetic materials. Below I used IrMn\Co\Ru to do this. In overall, this allows the upper Co layer to be pinned and the bottom layer to be the spin valve.
Another interesting fact of this time, was that a different type of effect was being researched vigorously: Tunnel Magnetoresistance (TMR). It’s fairly similar to a GMR except that electrons will travel with their spins perpendicular to the layers of the sensor.; also, the film stack now consists of: Ferromagnetic Layer\ Thin Insulating Layer \ Ferromagnetic Layer. The reason why this sensor is more appealing is because one is able to reduce the amount of magnetic grains required to write a bit. The way one does this is by making the magnetic media have its grain’s magnetization be perpendicularly oriented. Despite I have not mentioned it, an increase in data storage requires an optimization of the magnetic media, the read head, and the signal to noise ratio. A lot of the optimization that occurs between new methods of memory storage is a result of signal processing. Today, we are all enjoying higher density storage because of the introduction of theTMR read head sensor and perpendicular oriented magnetic media, and over the course of the next decade we will be having small increases in density storage as a result of signal processing. Presently, there is ongoing research to develop and optimize HAMR for next generation of hard drives.
The last topic I would like to cover is MRAM. In the early 2000’s plenty of research was performed in obtaining TMR sensors that could output high values of TMR, i.e. as an example in 2004 Parkin published the Fe\MgO\Fe which had an output of 200% TMR, and yet we have not been able to see a reliable and cost effective MRAM cell. This is because the incorporation of MRAM cell into an IC has to survive the CMOS process. In other words, the materials that make the MRAM cell have to survive various heating parameters that proven much more difficult to optimize than expected.
If someone has some kind of specific question about spintronics in magnetism, I will gladly answer them. My research focuses on this topic and frequency dependent magnetic materials, so I know a bit on this topic.
Thanks for sharing Sohini.
Cheers,
Sergio