Sep 06, 2013 |
Physicists find enhanced fluctuations in nanomagnets
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(Nanowerk News) 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.
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Their findings, which appear in the journal Physical Review B Rapid Communication ("Temperature dependence of the switching field in all-perpendicular spin-valve nanopillars"), 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.
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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.
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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.
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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.
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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.
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