Intermartensitic Transformation and Enhanced Exchange Bias in Pd (Pt) -doped Ni-Mn-Sn alloys

Abstract

In this work, we studied the phase transitions and exchange bias of Ni50−xMn36Sn14Tx (T = Pd, Pt; x = 0, 1, 2, 3) alloys. An intermartensitic transition (IMT), not observed in Ni50Mn36Sn14 alloy, was induced by the proper application of negative chemical pressure by Pd(Pt) doping in Ni50−xMn36Sn14Tx (T = Pd, Pt) alloys. IMT weakened and was suppressed with the increase of applied field; it also disappeared with further increase of Pd(Pt) content (x = 3 for Pd and x = 2 for Pt). Another striking result is that exchange bias effect, ascribed to the percolating ferromagnetic domains coexisting with spin glass phase, is notably enhanced by nonmagnetic Pd(Pt) addition. The increase of unidirectional anisotropy by the addition of Pd(Pt) impurities with strong spin-orbit coupling was explained by Dzyaloshinsky-Moriya interactions in spin glass phase.

Martensitic Transformation, Thermal Analysis and Magnetocaloric Properties of Ni-Mn-Sn-Pd Alloys

“…As showed in Figure 2, evidence is found that the 2 2 0 peak/reflection shifts to a lower angle when we increase the substitution of Ni by Pd, leading to the growth of cell volume. Analogous behaviour was also observed in Ni 50−x Mn 36 Sn 14 Pd x samples [15], confirming that this effect is probably due to the substitution of larger Pd addition (1.79 Å) in previous Ni sites (1.62 Å). It is known that the characteristic martensitic start transformation temperature in Heusler samples is powerfully affected by the Mn-Mn interatomic distances [19].…”

“…Processes 2020, 8, x FOR PEER REVIEW 4 of 14 behaviour was also observed in Ni50−xMn36Sn14Pdx samples [15], confirming that this effect is probably due to the substitution of larger Pd addition (1.79 Å) in previous Ni sites (1.62 Å). It is known that the characteristic martensitic start transformation temperature in Heusler samples is powerfully affected by the Mn-Mn interatomic distances [19].…”

“…Concerning Pd addition, S.Y. Dong et al have reported that the lattice parameter and the martensite transformation temperature increases gradually in Ni 50−x Mn 36 Sn 14 Pd x with the increase in Pd content [15]. Likewise, R. Saha et al have observed the same effect.…”

“…Likewise, the addition of a fourth element to Ni-Mn-Sn systems is a current strategy to tune the structural-magnetic transformations and the magnetic behaviour of SMAs, enhancing the properties even though it can also modify the structure [10]. Numerous quaternary systems have been established, such as those with the addition of Cu [11], Co [12], Fe [13], W [14] or Pd [15]. The additions usually produce a shift of the transformation temperatures.…”

“…A parameter has been defined that influences MT temperatures-e/a (average outer electron concentration per atom) [16], which offers a suitable way to control the transition temperature. Likewise, the stoichiometry Heusler structure is X 50 Y 25 Z 25 (also described as X 2 YZ) and some articles analyse the influence on the characteristic temperatures and magnetic response of the addition of a fourth element taking into account the expected site position of this additional element, usually X or Z sites [11,15].…”