Since the discovery of a purely thermally induced magnetisation switching (TIMS) in GdFeCo, there has been much effort to identify the cause of this unexpected phenomenon. While several works have studied the macroscopic relaxation behaviour (Mentink et al., Phys. Rev. Lett. 108, 057202 (2012). Atxitia et al., Phys. Rev. B 87, 224417 (2013)), there has been little headway made in finding the material origins of the switching. In our new work “Two-magnon bound state causes ultrafast thermally induced magnetisation switching” published in the open access journal Scientific Reports we have found, through simulation and described with a combination of theoretical approaches, that the switching is caused by angular momentum transfer from a two magnon bound state which exists in this class of ferrimagnetic materials. Specifically, within GdFeCo we have shown that the amorphous properties of the material affect the switching behaviour because the antiferromagnetic interactions which couple the rare-earth and transition metal species have a large effect only at the interfaces of Gd clusters within the FeCo background. Our work provides a new insight into the switching which is induced by femtosecond laser pulses and gives new directions for experimentalists to focus their research.
The first Ultrafast Magnetism Conference (UMC) was held last week in Strasbourg, France. A week focused on magnetism on the sub-picosecond timescale. Talks from both experimental and theoretical groups included talks on laser induced magnetization dynamics, THz stimulation and ultrafast magneto-acoustics.
This meeting was a huge success with over 150 participants from all over the world and a large number of invited talks. The format was a single session talks and posters so that all participants could see everything on offer. The single session format promoted a comfortable environment in which the audience could ask questions and discuss things amongst themselves.
I gave a contribution based on the thermally induced switching phenomena in GdFeCo, recently accepted to Nature Scientific Reports (the preprint can be found on arXiv). This work by Joe Barker shows that the thermally induced switching is caused by the excitation of a two magnon bound state. This bound state is possible when sufficient energy is provided to excite two spinwave bands. This lays out a criteria for ultrafast switching with heat to occur, which Joe tested using the atomistic spin model.
The second Ultrafast Magnetism Conference will take place in 2015 in Nijmegen, where I am sure the event will be even larger and the talks will be equally as interesting.