Invited Paper MI+TF-ThM5
Correlating Microstructure with Magnetic Properties Variation in Patterned Magnetic Nanostructures with Transmission Electron Microscopy

Thursday, October 21, 2010, 9:20 am, Room Zuni

Patterned magnetic nanostructures are keystone components in technologies such as hard drive media, sensors, and the magnetoresistive device variants (read-head, random access memory, logic). During manufacturing, different processes produce defects that are the source of variations in magnetic properties in magnetic nanostructures. One example is the Co/Pd nanodot array, interesting for its potential in realizing the bit-patterned media data storage platform. We showed that grains of a particular orientation formed during the film deposition can act as trigger sites for magnetization reversal. Therefore, the ease of switching a particular nanodot among millions of nominally identical nanodots depends on the random presence of trigger grains within it. When considered as an ensemble, the nanodot array will exhibit a switching field distribution; this is the superposition of the individual switching fields unique to each nanodot. In general, switching field distribution and other magnetic property variations in patterned magnetic nanostructures can present major problems for devices development where uniform magnetic performances are required.

The fact that magnetic phenomena in patterned magnetic nanostructures, whether it be magnetization reversal or magnetoresistance, are always observed as distributions means that it is import to identify the root causes to these distributions. An essential aspect to furthering the progress in developing magnetic nanostructure devices is therefore, to correlate nanostructure, defects and interfaces, and chemical composition to magnetic behaviors on the nanoscale. To this end, one of our main focuses is in developing ways to measure variations in magnetic properties using transmission electron microscopy (TEM). TEM is one of the few tools that can provide structural, chemical and magnetic information all at the same time.

In this presentation, I will highlight specific examples of measurements developed for patterned magnetic nanostructures using a TEM. The first example is the microstructure correlation to the switching field distribution in Co/Pd nanodots, described earlier. The second example is a set of in situ tunneling measurements where we succeeded in measuring unique energy barrier height and tunneling magnetoresistance (TMR) on fully functional nano-magnetic tunnel junctions (MTJ) built as a TEM sample. Finally, I will show how single nanostructure magnetometry can be achieved within a TEM.