Small hysteresis and giant magnetocaloric effect in Nb-substituted (Mn,Fe)2(P,Si) alloys

Viable Materials with a Giant Magnetocaloric Effect

“…Materials containing highly toxic arsenic include MnAs [123,131,210,238,245,246,256,265,273,276,282,289] and MnFe(P,As) [48,49,239,298]. However, interest is shifting towards less toxic materials without As, such as (Mn,Fe) 2 (P,Si) [125,126,150] doped with Ge [109,205] or B [184,201,215]. Examples with toxic antimony include Mn 1.9 Co 0.1 Sb [211], Mn 2−x Cr x Sb [236], NiMn 0.9 Sb 0.1 [254], Ni 0.5−x Co x Mn 0.38 Sb 0.12 [92], etc.…”

Setting the Basis for the Interpretation of Temperature First Order Reversal Curve (TFORC) Distributions of Magnetocaloric Materials

“…The effect is associated with significant magnetization changes driven by temperature and magnetic field, classifying the MC materials according to the order of their thermomagnetic phase transition: first-and second-order type [4]. Since the first experiments with pure Gd in 1976 [5], which undergoes a Curie transition (second-order type) from the ferromagnetic (FM) to the paramagnetic (PM) state, the interest has moved nowadays to those magnetocaloric materials which undergo magnetoelastic or magnetostructural transitions (first-order type) such as GdSiGe [6,7], LaFeSi [8,9], MnFePAs [10,11] or Heusler [12,13]-based alloys. Typically, these materials present higher MC response than those with second order transitions, although they have associated undesired thermal and magnetic hysteresis, which significantly reduces its response in cyclical conditions, limiting their applicability in refrigeration devices [14].…”

Effect of off-stoichiometry and Ta doping on Fe-rich (Mn,Fe)2(P,Si) based giant magnetocaloric materials

“…Different optimization strategies have been proposed to adjust the GMCE performance of (Mn,Fe) 2 (P,Si)-based MCMs like tuning the metallic (Fe-Mn) and nonmetallic (P-Si) ratios [7,8], chemical pressure engineering (substitutional/interstitial doping) including light elements doping (Li, B, C, N, F, S) [9][10][11][12], 3d transition metal doping (V, Co, Ni, Cu, Zn) [13][14][15], 4d transition metal doping (Zr, Nb, Mo, Ru) [16][17][18][19], other element doping (Al, Ge, As) [20][21][22][23] and nano-structuring [24]. Alloying with doping elements does not necessarily only tune the T tr (towards higher T tr -Li, B, C, Al, Ge, Zn and Zr; towards lower T tr -N, F, S, V, Ni, Co, Cu, Ge, Nb, Mo and Ru), but potentially also change the ΔT hys , which is detrimental to the cooling/heating efficiency [25].…”

“…With Ta doping the ΔT hys remains almost constant (about 5 K). This is the first experimental observation of a constant ΔT hys upon doping, which differs from the situation like doping with light elements (B, C, N, F, S) [10][11][12], doping with 3d transition metals (V, Co, Ni, Cu, Zn) [13][14][15] and doping with 4d transition metals (Zr, Nb, Mo, Ru) [16][17][18][19] and doping with other elements (Al, Ge, As) [20][21][22][23]. However, in comparison to Nb substitution, Ta (r = 1.70 Å) has a comparable covalent radius as Nb (r = 1.64 Å) [38], and therefore generally similar physical properties are expected as a result of the comparable chemical pressure.…”

“…Furthermore, as a chemical-twin element for Nb, doping with Ta in the (Mn,Fe) 2 (P,Si) MCMs behaves completely different from Nb. For example, Nb substitution leads to a continuous reduction in ΔT hys and an attenuated GMCE [17], The difference between Nb and Ta could be ascribed to the difference in electron configuration between Nb ([Kr]4d 4 5s 1 ) and Ta ([Xe] 4f 14 5d 3 6s 2 ) [49]. Although they contain the same number of valence electrons (e v = 5), Nb may easier form an effective p-d hybridization with metalloids (P/Si) because its 4d energy level is markedly lower than the 5d energy level, which could lead to a weaker p-d hybridization for the Ta doped system and affect the energy barrier of ΔT hys .…”