Crinkle cut magnets

Figure 1. A schematic illustration of how tilting ferromagnetic chains with strong single ion anisotropy can produce a noncollinear structure with a net moment

In most magnetic materials, the underlying atomic spins line up either parallel (ferromagnetic correlation) or antiparallel (antiferromagnetic correlation): they are collinear. In noncollinear magnets spins can arrange themselves in any direction relative to each other (depending on the interactions and geometry of the material) and these noncollinear spin textures can produce magnetic properties that are hard to realise otherwise, including electrical control over magnetic spin or nanometric magnetic data storage. Creating materials with these noncollinear structures is challenging, however, because they typically require multiple different spin-spin interactions to be competitive with each other.

In this paper, we make four new noncollinear magnets by reacting iron and nickel dichloride with the organic molecules pyrimidine and 2,1,3-benzothiadiazole. These layered materials are made of metal chloride chains connected by the organic molecules into 2D sheets. In each chain, the spins point in the same direction, but because the organic molecules are not linear, the ferromagnetic chains are tilted relative to each other creating corrugated sheets. This crinkled structure means that the spins on each chain are forced to be non-collinear and even better, have a net magnetic moment. This design strategy demonstrates how metal-organic materials can be used to design new and functional magnetic materials.

This work was carried out in collaboration with the University of Birmingham (theory), University of Cambridge (high field magnetic measurements) and Oak Ridge National Lab (neutron scattering), and emerged from a undergraduate masters project (Pete Speakman).