Physicists find enhanced fluctuations in nanomagnets

Sep 06, 2013

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 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 for magnetic memory-, such as in hard-disk drives and magnetic random access memories, in which 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 of the material characteristics fits the data well.

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More information: prb.aps.org/abstract/PRB/v88/i10/e100401

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