Electronic structure of some Heusler alloys based on aluminum and tin

We report on the magnetic properties and electronic structure of ${\mathrm{Cu}}_{2}\mathrm{CrAl},$ and ${\mathrm{Fe}}_{x}\mathrm{TiSn},$ ${\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Ni}}_{x}\mathrm{TiSn},$ and ${\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{TiSn}$ cubic solid solutions. The analysis of the magnetic susceptibility $\ensuremath{\chi}(T),$ electrical resistivity $\ensuremath{\rho}(T),$ and lattice thermal expansion $a(T)$ data allowed us to find the existence of a thermodynamic phase transition in all samples at $\ensuremath{\sim}240 \mathrm{K}.$ The observed anomalies at $\ensuremath{\sim}240 \mathrm{K}$ provide evidence of an isostructural phase transition which could be created by a large strain due to a small size of grains. ${\mathrm{Fe}}_{2}\mathrm{TiSn}$ was observed by high-resolution electron microscopy to be composed of nanosized solid solution grains of the order of 100 nm. We discuss the superparamagnetic behavior in these alloys which results from an atomic disorder.