MAGNETIC QUANTUM PHASE-TRANSITION IN MNSI UNDER HYDROSTATIC-PRESSURE

The crossover from a spin-polarized to nonpolarized state as a functio n of pressure (p) at low temperature (T) has been investigated in MnSi via high-precision measurements of the electrical resistivity rho and magnetic susceptibility chi. In the magnetic phase (p<p(c) similar or equal to 14.6 kbar), rho proportional to T-2 at low T as expected for a Fermi liquid in a weakly polarized state. In the nonmagnetic phase ( p>p(c)), rho vs T is consistent with the predictions for a marginal Fe rmi liquid model in which nearly critical spin fluctuations of long wa velength lead to a singular quasiparticle interaction. The transition is second order for p<psimilar or equal to 12 kbar and weakly first o rder in the range p<p<p(c), where the transition temperature T-c lies below a peak of chi vs T. The variation of T-c with p and of both rho and chi with T and p may be understood in terms of a model of quantum critical phenomena.