Squeezing the crystalline lattice of the heavy rare-earth metals to change their magnetic order: Experiment andab initiotheory

Ab initio electronic structure theory finds the type of magnetic order of the heavy rare earths to be correlated directly with the a and c lattice parameters of their hexagonal-close-packed crystal lattices. We refine our experimental data and obtain magnetic phase diagrams showing magnetic state and transition temperatures versus a and c for Tb and for the alloy Ho0.4Gd0.6. For both systems we mark out the boundaries in a and c space between incommensurate (helical) antiferromagnetic order and ferromagnetic states and find that these agree very well with the theoretical prediction as well as with each other. These data support the proposition of a universal ``crystallomagnetic'' phase diagram for the heavy rare earths.