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Anisotropic physical properties of the Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic

We have investigated anisotropic physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient and the thermal conductivity) of the single-crystalline Taylor-phase T-Al72.5Mn21.5Fe6.0 complex intermetallic that is an orthorhombic approximant to the d-Al-Mn-Pd decagonal quasicrystal. The measurements were performed along the a, b and c directions of the orthorhombic unit cell, where (a, c) atomic planes are stacked along the perpendicular b direction. The T-Al72.5Mn21.5Fe6.0 shows spin-glass behavior below the spin freezing temperature Tf ≈ 29 K with a small anisotropy in the magnetic susceptibility. The anisotropic electrical resistivities are rather large and show negative temperature coefficient. The resistivity is lowest along the stacking direction, which appears to be a common property of the decagonal approximant phases with a stacked-layer structure. The temperature-dependent resistivity was theoretically reproduced by the quantum transport theory of slow charge carriers. The thermopower is positive for all three crystallographic directions, indicating that holes are the majority charge carriers, and no anisotropy can be claimed within the experimental precision. The same conclusion on the holes being the dominant charge carriers follows from the Hall-coefficient measurements, which is a sum of the (positive) normal Hall coefficient and the anomalous term, originating from the magnetization. The anisotropy of the thermal conductivity is practically negligible. The T-Al72.5Mn21.5Fe6.0 Taylor phase can be considered as a "close-to-isotropic" complex intermetallic. The relation of the anisotropic physical properties of the Taylor phase to other families of decagonal approximant phases with the stacked-layer structure is discussed.

T-phases; complex intermetallic; hall effect; electrical conductivity; themal conductivity; thermopower

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