Spin Impurities in Noncollinear Antiferromagnets With Mn3pt As An Example

We develop a linearized theory for the classical Heisenberg model. which allows us to approximately solve for the local distortion of spins around an impurity in a non-collinear antiferromagnet. Provided that the ratio of disturbed to undisturbed bonds is small, the theory should be applicable. The theory is particularly useful when alloying lifts the degeneracy often found in non-collinear magnets. We look at the cases of gamma-Mn alloys in general, and Mn3Pt in particular. We can successfully predict the experimentally observed phase transitions caused by alloying in these materials, providing further evidence for the exotic 'hedgehog' phase.