Impact of F and S doping on (Mn,Fe)2(P,Si) giant magnetocaloric materials

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

“…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.…”

“…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].…”

“…The main parameters for the Ta doped alloys are summarized in Table 2. Precise atomic occupancies for highly ordered crystalline materials is indispensable to characterize their physical properties [11,12,40,41]. Although XRD cannot resolve the occupancy of Mn/Fe (similar structure factors), the position of the heavy element Ta can be uniquely determined at the substitutional 3g site.…”

“…The reduced T tr indicates the decreased magnetic exchange interaction [44]. However, covalent bonding is also pivotal for the magnetoelastic phase transition [42] and doping with different electronegativity elements can modify its bonding properties [12], and thereby change the band structure for this partially localized and itinerant system [45]. The already distinguished occupancy for the Mn/Fe/P/Si atoms obtained from previous neutron diffraction experiments [11,12,46] and the above DFT calculations make it possible to determine the interatomic distances of different metalmetal pairs using the XRD data, shown in Fig.…”

Magnetocaloric Effect in Lightly‐Doped Fe5Si3 Single Crystals

“…[2,9] So far, two types of firstorder magnetic transitions have been reported in giant MCE materials: type I is a first-order magneto-structural transition, as observed in Gd 5 Si 4-x Ge x , [10,11] Ni-Mn-(In, Sn, Sb)-based Heusler-type magnetic shapememory alloys, [4,12,13] and MnCoGeB x ; [14,15] type II relies on a magneto-elastic transition as found in MnFeP(As, Ge), [5,16,17] LaFe 13-x Si x H, [18,19] and Fe 2 P-based Mn-Fe-P-Si systems. [20,21] Generally, type I materials offer large MCEs, however, the accompanying thermal and magnetic hysteresis inhibits applicability. The lack of thermal and magnetic hysteresis of type II MCE materials makes them more desirable potential refrigerants.…”