  The crystal structure and magnetic properties of MnCoxFe1-xSi (x=0-0.5)
compounds were investigated. With increasing Fe content, the unit cell changes
anisotropically and the magnetic property evolves gradually: Curie temperature
decreases continuously, the first-order metamagnetic transition from a
low-temperature helical antiferromagnetic state to a high-temperature
ferromagnetic state disappears gradually and then a spin-glass-like state and
another antiferromagnetic state emerge in the low temperature region. The Curie
transition leads to a moderate conventional entropy change. The metamagnetic
transition not only yields a larger negative magnetocaloric effect at lower
applied fields than in MnCoSi but also produces a very large temperature span
(103 K for H=5 T) of delta S(T), which results in a large refrigerant capacity.
These phenomena were explained in terms of crystal structure change and
magnetoelastic coupling mechanism. The low-cost MnCo1-xFexSi compounds are
promising candidates for near room temperature magnetic refrigeration
applications because of the large isothermal entropy change and the wide
working temperature span.
