In a ferromagnet, combined forces are at work. In order for a compass needle to point north or a fridge magnet to stick to the fridge door, countless electron spins inside them, each of which only creates a tiny magnetic field, all need to line up in the same direction. This happens through interactions between the spins, which have to be stronger than the disordered thermal motion inside the ferromagnet. If the temperature of the material is below a critical value, it becomes ferromagnetic.
Conversely, to change the polarity of a ferromagnet one usually needs to first heat it up above its critical temperature. The electron spins can then re-orient themselves, and after cooling down the magnetic field of the ferromagnet eventually points in a different direction.
A team of researchers led by Ataç Imamoglu, Professor of Physics at ETH Zurich and Tomasz Smolenski, Professor at the University of Basel, have now managed to bring about such a re-orientation using only light – without any heating. They recently published their results in the scientific journal Nature.
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