Magnetic quantum phase transition in MnSi under hydrostatic pressure

The crossover from a spin-polarized to nonpolarized state as a function of pressure (p) at low temperature (T) has been investigated in MnSi via high-precision measurements of the electrical resistivity {ρ} and magnetic susceptibility {χ}. In the magnetic phase (ppc{}14.6 kbar), {ρ}{∝}T² at low T as expected for a Fermi liquid in a weakly polarized state. In the nonmagnetic phase (p>pc), {ρ} vs T is consistent with the predictions for a marginal Fermi liquid model in which nearly critical spin fluctuations of long wavelength lead to a singular quasiparticle interaction. The transition is second order for pp*{}12 kbar and weakly first order in the range p*{p}c$, where the transition temperature ${T}clies below a peak of χ vs T. The variation of{T}c$ with p and of both {ρ} and {χ} with T and p may be understood in terms of a model of quantum critical phenomena.