Magnetic structure

In the most simple (collinear) cases of antiferromagnetism, there is still a common quantization axis, but the electronic spins are pointing alternatingly up and down, leading again to cancellation of the macroscopic magnetization.

However, specifically in the case of frustration of the interactions, the resulting structures can become much more complicated, with inherently three-dimensional orientations of the local spins.

In this view, with increasing temperature the local magnetization would thus decrease homogeneously, as single delocalized electrons are moved from the up- to the down-channel.

Here, finite temperatures lead to a deviation of the atomic spins' orientations from the ideal configuration, thus for a ferromagnet also decreasing the macroscopic magnetization.

At a temperature above the ordering point of the magnetic moments, where the material behaves as a paramagnetic one, neutron diffraction will therefore give a picture of the crystallographic structure only.

Below the ordering point, e.g. the Néel temperature of an antiferromagnet or the Curie-point of a ferromagnet the neutrons will also experience scattering from the magnetic moments because they themselves possess spin.

More recently, table-top techniques are being developed which allow magnetic structures to be studied without recourse to neutron or synchrotron sources.

[8] Manganese (in the α-Mn form) has 29 atoms unit cell, leading to a complex, but commensurate antiferromagnetic arrangement at low temperatures (magnetic space group P42'm').