Calorimetric Investigation of Localized Magnetic Moments and Superconductivity in Some Alloys of Titanium with Manganese and Cobalt

The specific heats $C$ of arc-cast specimens of Ti and alloys of Ti with Mn and Co have been measured between 1.2 and 4.5°K. For ≈99.92 wt.% pure hcp Ti, the standard $C=\gamma T+\beta T^3$ relation is closely obeyed, with $\gamma =3.30\mathrm{}\pm 0.03$mJ/mole${\left(\mathrm{°}\mathrm{K}\right)}^2$ and ${\beta }^{-\frac{1}{3}}\propto {\theta }_D=429\mathrm{}\pm 7°$K. For hcp Ti alloys containing 0.17-1.7 at.% (nominal atomic percent) Mn we observe (1) a large excess specific-heat contribution which increases with decrease of temperature, evidently associated with ordering of magnetic moments localized at the Mn ions, and (2) no calorimetric evidence of a standard bulk superconducting transition. Neither a large localized-moment-type specific-heat contribution nor a standard bulk superconducting transition is calorimetrically observed in hcp Ti-1 at.% Co. The absence of standard bulk superconducting transitions in dilute hcp Ti-Mn and Ti-Co is in apparent conflict with earlier magnetic evidence for elevation of the superconducting transition temperature $T_c$ above 1.2°K in such alloys. That dilute Mn addition to the hcp Group-IV transition elements Ti or Zr actually lowers $T_c$ is suggested by the observation that 0.2 at.% Mn added to the superconducting alloy hcp Ti-50 at.% Zr [$T_c=1.60\mathrm{}°$K, $\gamma =4.2\mathrm{}$mJ/mole${\left(\mathrm{°}\mathrm{K}\right)}^2$, ${\theta }_D=304\mathrm{}°$K] (1) induces localized-moment behavior in the magnetic susceptibility and specific heat, (2) eliminates the standard bulk calorimetric superconducting transition, and (3) results in a broad and incomplete resistance-versus-temperature superconducting transition. In contrast to the behavior of hcp Ti-Mn and Ti-Zr-Mn alloys, a predominantly bcc Ti-14 at.% Mn alloy displays (1) standard normal-state specific-heat behavior with no evidence of localized moments, and (2) a standard calorimetric superconducting transition at $T_c=2.55\mathrm{}°$K. The formation and interaction of dilute localized moments in Ti and Ti-Zr, and the effect of the localized moments on superconductivity, are qualitatively discussed.