Impact of incomplete martensitic phase transition on the magnetic behavior of Co-doped MnNiGe1.05 alloys

Co-doped ${\mathrm{MnNiGe}}_{1.05}$ alloys of nominal compositions ${\mathrm{MnNi}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{Ge}}_{1.05}$ (for $x=0.075$ and 0.125), with a significant amount of vacancies at the transition-metal sites, have been explored through temperature-dependent structural and magnetic investigations. Such studies confirm the presence of martensitic phase transition (MPT) in both the alloys. However, the observed MPT is found to be incomplete in nature. The presence of a significant amount of high-temperature austenite phase, well below the MPT, results in several interesting features, including field-induced metamagnetic transition and nonmonotonic change in the inverse magnetocaloric behavior, etc. In addition, a possible spin-reorientation transition has also been noticed in the magnetically ordered austenite phase for both the alloys.