  An effective scheme of isostructural alloying was applied to establish a
Curie-temperature window in isostructural MnNiGe-CoNiGe system. With the
simultaneous accomplishment of decreasing structural-transition temperature and
converting antiferromagnetic martensite to ferromagnetic state, a 200 K
Curie-temperature window was established between Curie temperatures of
austenite and martensite phases. In the window, a first-order magnetostructural
transition between paramagnetic austenite and ferromagnetic martensite occurs
with a sharp jump in magnetization, showing a magnetic entropy change as large
as -40 J kg-1 K-1 in a 50 kOe field change. This giant magnetocaloric effect
enables Mn1-xCoxNiGe to become a potential magnetic refrigerant.
