Iron and copper are both magnetic, but only iron sticks to your refrigerator. That’s because iron is ferromagnetic at room temperature, while copper is paramagnetic. For a material to have two types of magnetism simultaneously at one temperature is uncommon. To have three types simultaneously is exceedingly rare. The alloy NbFe2 is one of those rare materials: at low temperatures it is ferromagnetic, paramagnetic and antiferromagnetic. But why? Researchers have discovered that this odd behavior in a metal is actually caused by a “lucky accident”, rather than a complex interaction between electrons, as had previously been suspected. Just the right ratio of niobium to iron causes the chemistry and structure to produce an interesting electronic feature that explains all of the exotic properties of this material in detail, even the ideal ratio for this to happen. Although the behavior is exotic, the origin is not — but it is exceptional. Knowing about this kind of natural “accident” may lead to the discovery of yet more unusual magnetic materials.
A. Alam and D. D. Johnson “Chemically Mediated Quantum Criticality in NbFe2” Physical Review Letters 107 (2011) 206401. DOI 10.1103/PhysRevLett.107.206401