PerspectiveMagnetic Materials

An attractive, reshapable material

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Science  19 Jul 2019:
Vol. 365, Issue 6450, pp. 219
DOI: 10.1126/science.aax8979

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Summary

Permanent magnets are made from ferromagnetic materials like iron. An external magnetic field can align the electron spins, and strong spin-spin interactions can keep the spins aligned even after the field is removed. This remanent magnetization remains unless the material is heated above its Curie temperature, at which point thermal agitation overcomes the spin coupling and spins become disordered (1). Materials with weaker spin-spin interactions, such as aluminum and ferrous oxide, can form paramagnets, which become magnetized only when an external field is applied. The strong spin-spin interactions underlying ferromagnetism would seem to require the close atomic proximity found in dense solids. However, on page 264 of this issue, Liu et al. (2) present a way to prepare soft, reconfigurable millimeter-size magnets prepared from small droplets of ferrofluid (3) in water.

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