A rapid and anisotropic modification of the Fermi-surface shape can be
associated with abrupt changes in crystalline lattice geometry or in the
magnetic state of a material. In this study we show that such an electronic
topological transition is at the basis of the formation of an unusual
pressure-induced tetragonal ferromagnetic phase in Fe1.08Te. Around 2 GPa,
the orthorhombic and incommensurate antiferromagnetic ground-state of
Fe1.08Te is transformed upon increasing pressure into a tetragonal
ferromagnetic state via a conventional first-order transition. On the other
hand, an isostructural transition takes place from the paramagnetic
high-temperature state into the ferromagnetic phase as a rare case of a `type
0' transformation with anisotropic properties. Electronic-structure
calculations in combination with electrical resistivity, magnetization, and
x-ray diffraction experiments show that the electronic system of Fe1.08Te
is instable with respect to profound topological transitions that can drive
fundamental changes of the lattice anisotropy and the associated magnetic
order.Comment: 7 pages, 4 figur