On beating the superparamagnetic limit with exchange bias. R. F. L. Evans1, R. Yanes2, O. Mryasov3, R. W. Chantrell1 and O. Nature. Jun 19;() Beating the superparamagnetic limit with exchange bias. Skumryev V(1), Stoyanov S, Zhang Y, Hadjipanayis G, Givord D. Request PDF on ResearchGate | On beating the superparamagnetic limit with exchange bias | Interest in magnetic nanoparticles has increased.

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We demonstrate this principle for ferromagnetic cobalt nanoparticles of about 4 nm in diameter that are embedded in either a paramagnetic or an antiferromagnetic matrix. Here we show that magnetic exchange coupling induced at the interface between ferromagnetic and antiferromagnetic systems can provide an extra source of anisotropy, leading to magnetization stability. Thus, the demand for further miniaturization comes into conflict with the superparamagnetism caused by the reduction of the anisotropy energy per particle: Evans 1R.

Mryasov 3R.

Most applications rely on the magnetic order of the nanoparticles being stable with time. Whereas the cobalt cores lose their magnetic moment at 10 K in the first system, they remain ferromagnetic up to about K in the second. However, with decreasing particle size the magnetic anisotropy energy per particle responsible for holding the magnetic moment along certain directions becomes comparable to the thermal energy.


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On beating the superparamagnetic limit with exchange bias

This behaviour is ascribed to the specific way ferromagnetic nanoparticles couple to an antiferromagnetic matrix. Chantrell 1 and O.

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Beating the superparamagnetic limit with exchange bias.

It has a worldwide membership of around 50 comprising physicists from all sectors, as well as those with an interest in physics. Get permission to re-use this article. Click superparammagnetic to close this overlay, or press the “Escape” key on your keyboard.

Sign up for new issue notifications. Interest in magnetic nanoparticles has increased in the past few years by virtue of their potential for applications in fields such as ultrahigh-density recording and medicine. For systems with large values of the superparamagneric coupling, the ferromagnetic core is found to be unconditionally stable in the bias direction.

Beating the superparamagnetic limit with exchange bias.

In order to limi the possibility of “beating the superparamagnetic limit with exchange bias” Skumryev V. Evans et al EPL 88 As a federation of National Physical Societies, the EPS studies issues of concern to all European countries relating to physics research, science policy and education.


As a learned society, the EPS engages in activities that strengthen ties among the physicists in Europe. Yanes 2O.

Beating the superparamagnetic limit with exchange bias – Dimensions

When this happens, the thermal fluctuations induce random flipping of the magnetic moment with time, and the nanoparticles lose their stable magnetic order and become superparamagnetic. Such a system is ideal for thermal stability since there is no energetically stable reversed state, providing the antiferromagnetic shell is unchanged.

To find out more, see our Privacy and Cookies policy. In order to permit magnetic recording, which essentially requires a bi-stable system, we propose a heat-assisted recording method, whereby both the ferromagnet FM and antiferromagnet AF are switched.

This site uses cookies. Its publishing company, IOP Publishing, is a world leader in professional scientific communications. Our results show that exchange-biased systems exhibit an increased energy barrier along the bias direction, with a corresponding decrease of the barrier in the opposite direction.