Low Temperature Specific Heat and Magnetic Susceptibility of NbTi and NbTiMn Alloys

Abstract

We report on the results of a low temperature specific heat and magnetic susceptibility studies of a series of annealed-and-quenched binary NbTi alloys in the concentration range 41~53 wt.% Nb, which includes most compositions of technical interest. Also discussed is the influence of Mn on the calorimetrically measured properties of NbTi. Three series of alloys are considered: (i) a set of binary control alloys; (ii) alloys with Mn content fixed at ~0.5 wt.% and with Nb concentration between about 41 and 53 wt.%; (ii) alloys with an almost fixed Ti content (~46 wt.%) and with Mn concentration between 0 and ~5 wt.%. In alloys such as Ti-52Nb it is demonstrated that the addition of several percent of Mn causes a decrease in the electronic specific heat coefficient and a concomitant decrease in Tc. In that regard the effect of Mn on Tc (dTc/dc = -0.22 K/at.%) is comparable to that of Cr, Mo, or Re (for which dTc/dc = -0.2 K/at.%). It is concluded: (i) that Mn is a strong stabilizer of the bcc phase in Ti-base alloys; (ii) that Mn in bcc NbTi acts like any other nonmagnetic transition-element and influences Tc through its influence on the band density of states.