Modeling Slater-Pauling curves

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Abstract
The net magnetic moment per transition‐metal (TM) atom in a series of alloys varies with TM content in a way that is readily interpreted in terms of the band model of magnetism. Such Slater‐Pauling‐like curves for glassy metallic alloys of the form TM80P10B10 1 (at.%) and for crystalline TM borides, 2 (TM)2 B and TM B, show characteristic departures from the standard Slater‐Pauling curve for crystalline alloys. When metalloids are present, 1) the curves are shifted on a TM‐content scale, 2) their peaks are depressed, and 3) a steeper slope is observed in the data for the metamagnetic alloys (V, Cr or Mn in Fe). To investigate these differences, the rigid band model is examined using three densities of states: D (E) =constant, D (E) ∝1/2, and D (E) ∝E. Assuming the Goodenough3 form of d‐band exchange splitting, Δ, only the latter two densities of states allow for strong ferromagnetism (Δ≳Eo−EF, where Eo is the energy at the top of the minority‐spin sub‐band). These models also that the Goodenough splitting is inadequate when the data peaks much below (<90% of) 2.5 μB/metal atom and the slope to the right of the peak remains approximately 1 μB/valence electron. The shift in the data for the TM borides relative to the standard Slater‐Pauling curve is interpreted on the basis of these models to show that the TM d‐bands attract 1.6 electrons per boron atom present. The glassy TM80P10B10 alloys show less charge transfer, an average of 1.5 electrons per metalloid atom. This hybridization of metalloid conduction bands with TM d‐bands (or alternatively, the mediation by the matalloids of a greater degree of overlap between TM d‐levels) increases the itinerant character of the d‐bands, lowering their density of states and hence their exchange splitting. This accounts for the depressed peak in the data for metalloid‐containing alloys. The broader d‐bands also bias the alloys toward the antiferromagnetic state. Thus the addition of an anticoupling metal (e.g., Mn, Cr or V in Fe) to an alloy more effectively reduces the net moment when a metalloid is present. This explains the steeper slopes observed in the data for the metamagnetic alloys.

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