In this work is studied the electronic structure and phase stability of orthorhombic (B31) β-MnAs, which is compared with hexagonal (B8 _2) α-MnAs. In both phases the magnetic moment on the Mn atom decreases monotonically under lattice compression. The electronic effect which arises from the α→β geometrical distortion with increasing temperature is reminiscent of a second-order static JahnTeller effect. From the characteristics of the calculated Fermi surfaces is found evidence for the larger resistivity experimentally observed in the β-phase, which exhibits unfavorable conditions for the formation of open orbits. The results indicate that the structural transition (318 K) is driven by nesting of the Fermi surfaces.
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