Large, low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

•The effect of element substitution on the tricritical behavior of MnCoSi is studied.•Replacing Mn with Co is the most efficient way to reduce the critical field.•Large reversible magnetostriction is achieved under low field at room temperature.•The influence of valence electron concentration on the critical field is revealed.