Magnetization scaling in the paramagnetic phase of Mn1-xFexSi solid solutions

The magnetization field and temperature dependences in the paramagnetic phase of Mn1-xFexSi solid solutions with x<0.3 are investigated in the range B<5 T and T<60 K. It is found that field dependences of the magnetization M(B,T=const) exhibit scaling behavior of the form Bpartial M/partial B-M=F(B/(T-Ts)), where Ts denotes an empirically determined temperature of the transition into the magnetic phase with fluctuation driven short-range magnetic order and F(c{hi}) is a universal scaling function for given composition. The scaling relation allowed concluding that the magnetization in the paramagnetic phase of Mn1-xFexSi is represented by the sum of two terms. The first term is saturated by the scaling variable c{hi}=B/(T-Ts), whereas the second is linearly dependent on the magnetic field. A simple analytical formula describing the magnetization is derived and applied to estimates of the parameters characterizing localized magnetic moments in the studied system. The obtained data may be qualitatively interpreted assuming magnetic inhomogeneity of the paramagnetic phase on the nanoscale.

Spin excitations of the correlated semiconductor FeSi probed by THz radiation

By direct measurements of the complex optical conductivity $sigma( u)$ of FeSi we have discovered a broad absorption peak centered at frequency $ u_{0}(4.2 K) approx 32 cm^{-1}$ that develops at temperatures below 20 K. This feature is caused by spin-polaronic states formed in the middle of the gap in the electronic density of states. We observe the spin excitations between the electronic levels split by the exchange field of $H_{e}=34pm 6 T$. Spin fluctuations are identified as the main factor determining the formation of the spin polarons and the rich magnetic phase diagram of FeSi.