Semiconductor-metal transition in FeSi in an ultrahigh magnetic field

We study the conductivity and magnetic susceptibility of single-crystal iro n monosilicide in ultrahigh magnetic fields (up to 500 T) at low temperatur es. The experimental methods used in measuring the conductivity and magneti c susceptibility are discussed. At 77 K we detect a gradual increase in the conductivity of iron monosilicide by more than a factor of 100 as the magn etic field gets stronger. At 4.2 K we detect a first-order phase transition in a field of 355 T accompanied by a sudden change in the value of the mag netic moment by 0.95 mu(B) per iron atom and a transition to a phase with h igh conductivity. The results are discussed within the scope of the spin-fl uctuation theory. (C) 1999 American Institute of Physics. [S1063-7761(99)02 011-9].