Physicists find enhanced fluctuations in nanomagnets

NYU physicists have discovered that nanomagnets—a billionth of a meter in size—with a preferred up or down magnetization are sensitive to heating or cooling, more than expected.

Their findings, which appear in the journal Physical Review B Rapid Communication, suggest that a widely used model to describe the reversal of nanomagnets needs to be modified to account for temperature-dependent changes in the magnetic properties of the materials.

It is known that nanomagnets never switch at the same field each time – rather, random fluctuations in thermal energy generate a distribution of switching fields. But what's less clear is the origin of this phenomenon.

Developing a firmer understanding of the "activation energy" of nanomagnets is important in designing magnetic materials for magnetic memory-storage applications, such as in hard-disk drives and magnetic random access memories, in which random fluctuations can lead to data loss.

In their study, conducted in the laboratory of NYU physicist Andrew Kent, the researchers used a common approach to detect the activation energy barrier by measuring the distribution of switching fields across a wide temperature range.

The researchers discovered that changes in temperature were accompanied by changes in the height of the activation energy barrier. This resulted in a breakdown of the standard model, which assumes that the activation energy is temperature independent. This assumption works in earlier studies conducted over a limited range of temperatures. A modified model that considers the temperature dependence of the material characteristics fits the data well.