Quantum criticality on ferromagnetic systems: it is not where you think it is!

When a ferromagnetic-paramagnetic transition is tuned to $0$~K by application of pressure in clean systems, the transition becomes of the first order at a tricritical point before disappearing. Instead of having a quantum critical point, i.e. a second order transition at $0$~K, there is a quantum phase transition of the first order. The quantum phase transition can be from a ferromagnetic to a paramagnetic phase, or to a spatially modulated phase. We illustrate this case on a new material: LaCrGe$_3$. We will present the temperature-pressure-magnetic field phase diagram of LaCrGe$_3$ and show that quantum criticality is avoided by the appearance of a modulated phase. We will also explain how quantum criticality can be re-introduced. Work at Ames Laboratory was supported by US DOE under the Contract No. DE-AC02-07CH11358. Magnetization measurements under pressure were supported by Ames Laboratory's laboratory-directed research and development (LDRD) funding.