Some observations of the temperature dependences of magnetic susceptibility of titanium and titanium-aluminum alloys

The magnetic susceptibilities (χ) of a series of single-phase Ti-Al alloys have been measured in the temperature range 74-400 K. In addition, the susceptibility temperature dependences, χ parallel ( T ) and χ perpendicular ( T ), of single crystal specimens of pure Ti and the intermetallic compound Ti 3 Al were measured and correlated with the results of lattice-parameter ( c, a ) thermal expansion studies. In pure Ti, both χ parallel ( T ) and χ perpendicular ( T ) (4.2-400 K) are relatively temperature independent below about 70 K, the range within which the volume thermal expansion coefficient is practically zero; and increase linearly above about 130 K, in which region c and a both expand linearly. For Ti 3 Al, changes of slope of χ parallel ( T ) and χ perpendicular ( T ) (78-400 K) occurring near 200 K and 300 K were accompanied by distinct changes in the rates of thermal expansion of c and a . As a result of these and other experiments, several statements could be formulated relating to the susceptibility temperature dependences, χ( T ), of Ti and Ti-Al alloys: (i) χ( T ) was strongly responsive to thermally-induced lattice-parameter changes: (ii) for a family of Ti-Al solid solutions, χ( T ) was relatively insensitive to solute concentration; (iii) the total susceptibility was anisotropic; (iv) of the total susceptibility, only about one-third could be accounted for by the calorimetrically measured Fermi density-of-states, n ( E F ), the remainder being due chiefly to orbital paramagnetism; (v) curvature of n ( E )] E = E F is incapable of accounting for χ( T ) in the systems under study. To satisfy the experimental observations it was suggested that the principal mechanism for susceptibility temperature dependence in Ti and Ti-Al alloys is lattice-expansion-induced variation of the orbital paramagnetism.