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Memory capacity dependent on material size

Posted: 19 Feb 2014     Print Version  Bookmark and Share

Keywords:A*STAR Data Storage Institute  magnetic nanostructure  ferromagnetic resonance 

A team of scientists at the A*STAR Data Storage Institute, A*STAR National Metrology Centre and National University of Singapore have looked into the idea that patterning magnetic materials with nanometer-scale structures will help the development of non-volatile electronic memories with large storage capacities and no moving parts.

Kwaku Eason, Maria Sabino and their co-workers have modeled the changes in the characteristics of magnetic materials as devices are reduced in size to the nanoscale. However, material properties at such tiny dimensions are not always the same as those of larger structures.

in-plane ferromagnetic-resonance

The in-plane ferromagnetic-resonance response of a magnetic nanostructure changes with device size, shown here in the simulation results by the rapidly varying colors. The out-of-plane response, on the other hand, is relatively constant. (2014 A*STAR Data Storage Institute)

The researchers focused their attention on modeling a powerful and widespread tool for characterizing magnetic materials called ferromagnetic resonance (FMR). FMR measures the absorption of microwave radiation by a thin sample. Knowing which microwave frequencies are absorbed the most can provide a number of key material properties. One such crucial property is the damping parameter, which is an indicator of how quickly a memory made from the magnetic material can store and release data.

The team employed a mathematical tool, known as the finite element method, to simulate a simple cylindrical nanodevice in all three dimensions. By calculating the energy levels of the device in an external magnetic field, the team could predict the FMR signal for devices of varying sizes.

The researchers compared their simulations to experimental data obtained on nanodisks made of a nickel-iron alloy, known as permalloy, and found good agreement for all device sizes. "Other groups have provided additional experimental results that further confirm the accuracy of our predictions," said Eason.

The ability to predict the damping parameter of nanostructured magnetic materials is important because it is difficult to experimentally measure this property, partly because FMR signals from tiny targets are usually weak. Instead, researchers must study much larger devices and hope that the damping parameter is similar for nanostructures.

Recent experiments have conflicted on this point of scale. "One research group found from their experiments that device size does not matter in the damping measurement, while another group found that it does," explained Eason. "We have resolved this dilemma: it turns out that they were both right." Sabino added: "The results were contradictory because of the different material properties."

The simulations showed that the in-plane magnetic properties are sensitive to the dimensions of the device, whereas the out-of-plane properties are constant.

"Contributing to a clear understanding of this effect is one of the most gratifying parts of this work," stated Eason.

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