Itinerant-electron metamagnetism of MnSi at high pressure

Metamagnetic behaviors observed recently for MnSi at high pressure are discussed by using the electronic structures calculated in a self-consistent linear muffin-tin orbital method within the atomic-sphere approximation. It is shown that the ferromagnetic state with the moment larger than about $0.4{\mu }_{\mathrm{B}}/\mathrm{Mn}$ is stable at large lattice constants, while the paramagnetic state becomes stable at smaller lattice constants. By the fixed-spin-moment method the difference $\Delta E\left(M\right)\mathrm{}$ between the total energies of the ferromagnetic and paramagnetic states is calculated as a function of magnetic moment M near the critical lattice constant. The calculated $\Delta E\left(M\right)\mathrm{}$ is fitted to a form of the power series of $M^2$ up to the term of $M^{10}.$ Pressure dependences of the magnetization and susceptibility observed for MnSi are compared with the calculated results. Temperature dependences of the metamagnetic transition and susceptibility are also discussed by taking into account the effects of spin fluctuations and by using the expansion coefficients in the calculated $\Delta E\left(M\right).$ Metamagnetic behaviors observed for MnSi at high pressure are shown to be described very well by the present model.