Superconductivity and Localized Magnetic States in Ti-Mn Alloys

Evidence for superconductivity (Matthias et al.) and for localized magnetic states (Hake, Leslie, and Berlincourt) in the dilute hcp alloys of Ti-Mn has been given previously. In this paper, detailed studies are described which indicate that the superconductivity observed previously in the dilute (1 to 5 at.% Mn) alloys was due to retained enriched bcc inclusions and not proper to the hcp matrix itself. Curie-Weiss susceptibility behavior is observed in dilute (0.2-4 at.%) Ti-Mn confirming the existence of localized magnetic states in the hcp phase. The magnitude of the Curie constant (typically ≈ ${10}^{-4\mathrm{}}$ emu/g) suggests that magnetic moments ($\mu \approx 3.5$ μB/atom) are localized at the sites of Mn atoms in the hcp ($\alpha$ or ${\alpha }^{\prime }$) phases of the alloys. No Curie-Weiss behavior is observed in bcc ($\beta$) Ti-Mn. Annealing and quenching techniques were employed to prepare single phase hcp specimens and two-phase specimens consisting of bcc filaments in an hcp matrix. The former are not superconducting down to 1°K; the latter have zero resistance at the temperature coinciding with the $T_c$ of bulk bcc specimens. It is concluded that localized magnetic states suppress superconductivity in hcp Ti-Mn, while in the bcc phase $T_c$ is elevated commensurately with expected changes in the electronic state density $N\left(0\right)\mathrm{}$. In consequence, the existing experimental evidence on this system should not be interpreted in support of a magnetic-interaction hypothesis for superconductivity.