Credit: © 2009 ACS

Memory devices containing hard disk drives depend on the magnetic interaction between the reading and recording head and the data bits of the storage material. With data density continually increasing, understanding these materials and their interactions on an ever-decreasing scale becomes more and more important.

Now, Aurélien Masseboeuf and colleagues have used electron holography to quantitatively examine the nanoscale magnetic flux distribution in a magnetic film (pictured; Nano Lett. doi:10.1021/nl900800q; 2009). The film consists of ordered and disordered domains of iron–palladium on magnesium oxide. Electron holography can separate the magnetic and electrostatic contributions in the reconstructed phase, so simply inverting the sample means the electrostatic component can be removed.

Masseboeuf and colleagues observed that the magnetic domains in the ordered FePd phase were flattened near to the disordered layer, as can been seen at the bottom of the image. Compared with a calculated model, the walls between domains were thicker. The magnetic flux could be accurately measured inside and outside the sample, so the stray field can be related to the magnetization within the domains. These stray fields are the bit information for the reading heads, so this level of understanding should aid the development of improved magnetic data storage media.