Tuning of the Structure and Magnetocaloric Effect of Mn1−xZrxCoGe Alloys (Where x = 0.03, 0.05, 0.07, and 0.1)

Abstract

The aim of the present work is to study the influence of a partial substitution of Mn by Zr in MnCoGe alloys. The X-ray diffraction (XRD) studies revealed a coexistence of the orthorhombic TiNiSi-type and hexagonal Ni2In- type phases. The Rietveld analysis showed that the changes in lattice constants and content of recognized phases depended on the Zr addition. The occurrence of structural transformation was detected. This transformation was confirmed by analysis of the temperature dependence of exponent n given in the relation ΔSM = C·(BMAX)n. A decrease of the Curie temperature with an increase of the Zr content in the alloy composition was detected. The magnetic entropy changes were 6.93, 13.42, 3.96, and 2.94 J/(kg K) for Mn0.97Zr0.03CoGe, Mn0.95Zr0.05CoGe, Mn0.93Zr0.07CoGe, and Mn0.9Zr0.1CoGe, respectively. A significant rise in the magnetic entropy change for samples doped by Zr (x = 0.05) was caused by structural transformation.

Critical Behavior Studies in the Vicinity of the Curie Temperature in the MnCoGe Alloy

“…Taking into account values of exponents β and γ delivered by the Kouvel-Fisher method and equation (7), the exponent δ is 2.935. Another way to determine exponent δ is based on a simple modification of (3).…”

“…where ε = (T − T C )/T C , f ± mean regular functions with f + and f − for T > T C and T < T C , respectively. Relation (7) shows dependence between M (H, ε)ε −β and Hε −(β+γ) . Such construction with correct critical exponents should produce two universally different curves: (i) first for temperatures higher than T C and (ii) second one for temperatures lower than T C .…”

“…Moreover, rare earth-transition metal alloys, i.e., Gd 5 Ge 2 Si 2 -or La(Fe,Si) 13 -type [1][2][3][4], are also characterized by relatively good magnetocaloric properties. For several years, the MM'X group of alloys (M and M' denote 3d transition elements, and X denotes main group elements) have been intensively studied due to their excellent magnetocaloric properties [5][6][7][8]. The MM'X family of alloys manifests good physical properties and promising application potential.…”

The magnetocaloric effect properties for potential applications of magnetic refrigerator technology: a review

“…94 Kutynia and Gebara reported on Mn 1− x Zr x CoGe materials with x = 0.03, 0.05, 0.07, and 0.1, showing −Δ S max M values with a range 2.94 to 13.42 J kg −1 K −1 . 87 In summary, the investigations mentioned above indicate that composition, structure, and doping determination play crucial roles in determining the magnetocaloric properties of Heusler alloys. The comprehensive performance summary of MCE in Heusler alloys is provided in Table 2.…”

“…Heusler alloys have two general formulas both A 2 BC (full Heusler) and ABC (half Heusler), where A and B are filled with transition metal elements, and C is filled with elements from groups III-IV A. 86,87 Fig. 3(A) illustrates the structure of full Heusler (a) and half Heusler (b).…”