Magnetostructural transition in Co-Mn-Ge systems tuned by valence electron concentration

The effects of annealing process and chemical pressure on the structural and magnetocaloric properties of CoMn1-xVxGe (x=0.05 and 0.10) alloys have been studied. Rietveld refinement of XRD patterns revealed that all samples are single phase and they crystallize in hexagonal structure with a space group (P6(3)/mmc) at room temperature. The structural phase transition temperature T-struct decreases with increasing vanadium (V) content drastically in compare to CoMnGe alloy which exhibit a first order structural transition at around 450 K. The decrease in T-struct. by substituting fourth element in CoMnGebased alloys are discussed in frame of changing its valence electron concentration (e/a) values. We found that, alloys exhibiting a first order magneto-structural transition (FOMT) around room temperature, have an e/a value of 6.62-6.67. The e/a dependence of the magnetostructural transition temperature can be used as a guide to obtain an alloy with FOMT around room temperature. (C) 2019 Elsevier B.V. All rights reserved.