Laser-induced ultrafast spin reorientation in the antiferromagnet TmFeO3

All magnetically ordered materials can be divided into two primary classes: ferromagnets(1,2) and antiferromagnets(3). Since ancient times, ferromagnetic materials have found vast application areas(4), from the compass to computer storage and more recently to magnetic random access memory and spintronics(5). In contrast, antiferromagnetic (AFM) materials, though representing the overwhelming majority of magnetically ordered materials, for a long time were of academic interest only. The fundamental difference between the two types of magnetic materials manifests itself in their reaction to an external magnetic field-in an antiferromagnet, the exchange interaction leads to zero net magnetization. The related absence of a net angular momentum should result in orders of magnitude faster AFM spin dynamics(6,7). Here we show that, using a short laser pulse, the spins of the antiferromagnet TmFeO3 can indeed be manipulated on a timescale of a few picoseconds, in contrast to the hundreds of picoseconds in a ferromagnet(8-12). Because the ultrafast dynamics of spins in antiferromagnets is a key issue for exchange-biased devices(13), this finding can expand the now limited set of applications for AFM materials.