Polarized neutron scattering has been used to determine the changes in the distribution of unpaired electrons which take place in the martensitic transition in Ni2MnGa. Ni2MnGa is a ferromagnetic Heusler alloy which undergoes a reversible transition at about 220 K from a high temperature cubic phase to a low temperature tetragonal one. It has been suggested, on the basis of band structure calculations, that the structural phase transition is driven by a band Jahn-Teller distortion involving redistribution of electrons between 3d sub-bands of different symmetries. The results of the neutron scattering experiments show that the transition from the cubic to the tetragonal phase is accompanied by a transfer of magnetic moment from Mn to Ni. The unpaired electrons in the cubic phase have overall eg symmetry. In the tetragonal phase, the degeneracy of the eg and t2g bands is raised and the unpaired electrons are redistributed in such a way that the sub-bands based on orbitals extending towards the c-axis are preferentially occupied. Although the experimental moments differ in detail from those expected from band structure calculations, the change in symmetry of the magnetization distribution is consistent with a band Jahn-Teller origin for the phase transition.

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The magnetic moments in the triangular antiferromagnetic CsMnBr3 order at TN=8.3 K with a frustration of the magnetic moments in a 120° type magnetic structure. The magnetic moments are either ordered in a clockwise or an anticlockwise direction resulting in a chirality ordering, which is characterized by the critical exponent of the magnetic sublattice magnetization β=0.25. It has been shown that an electric field applied along the [110] direction removes the chiral ordering and a linear Ising-like phase will be established; consequently, the value of β decreases. The subsequent application of a magnetic field of B=4 T along the [100] direction causes the critical exponent β to increase. The magnetic phase diagram of CsMnBr3 does not change due to the introduction of an electric field.