Role of local disorder in martensitic and magnetic interactions in Ni–Mn based ferromagnetic shape memory alloys

Abstract

Extended X‐ray absorption fine structure (EXAFS) and X‐ray magnetic circular dichroism (XMCD) spectroscopy have been employed to understand the factors responsible for martensitic transformation in Ni–Mn based ferromagnetic shape memory alloys. Local structural distortions have been found even in the austenitic phase in Ni2Mn1.4Z0.6 (Z = Sn and In) alloys. Systematic investigations on Ni2Mn1+xIn1−x (x = 0, 0.3, 0.4, 0.5, and 0.6) reveal a progressive difference between Ni–In and Ni–Mn nearest neighbor bond distances that drive these alloys to martensitic transformation. Thermal evolution of Ni–Mn and Mn–Mn bond distances in the martensitic phase gives a clear evidence of a close relation between structural and magnetic degrees of freedom in these alloys. X‐ray absorption spectroscopy along with XMCD studies highlight the role of Ni 3d–Mn 3d hybridization in the magnetism of the martensitic phase of these alloys.

Long- and short-range order in the Ni52Co2Fe20Ga26 ferromagnetic Heusler alloy

“…As seen in Table 1, the martensitic transformation of Ga26 leaves almost unchanged the nearest-neighboring shell of iron (eight Ni), with a slight increase in the Fe-Ni distance from 2.48 to 2.51 Å and therefore a certain weakening of the Fe3d-Ni3d state hybridization. This is similar to the lengthening of the Mn-Ni bonds in Ni-Mn-Ga alloys upon MT (Sathe et al, 2013), but at variance with the shortening of these bonds in Ni-Mn-In alloys on the same transition (Priolkar et al, 2011;Priolkar, 2014). This suggests that Ni3d-Mn3d hybridization significantly influences the strength of the ferromagnetic or antiferromagnetic interactions in the martensitic phase of the Ni-Mn-In system, while in the Ni-Fe-Ga and Ni-Mn-Ga alloys the role of the Ni3d-Fe3d and Ni3d-Mn3d hybridizations, respectively, in martensite magnetism is diminished with respect to the Ni3d-Ga4p hybridization.…”

“…Similar values of the L2 1 lattice constant were found for Ni 51 Fe 22 Ga 27 , Ni 51 Fe 24 Ga 25 (Du et al, 2011) One can see a marked increase in the structural disorder beyond the nearest Ni1 neighbors, with almost the same degree of disorder ( 2 ) for the higher neighboring shells. This structural disorder could be responsible for a certain instability of the system, thus favoring its transition to the martensite on a decrease in temperature (Priolkar et al, 2008;Priolkar, 2014).…”

“…A great amount of XAS work has been carried out to investigate the geometric and electronic structures of ternary Heusler alloys, such as Ni-Mn-X (X = In, Sn, Sb) (Bhobe et al, 2008a,b;Priolkar et al, 2008Priolkar et al, , 2011Priolkar et al, , 2013Lobo et al, 2010Lobo et al, , 2017Priolkar, 2014;Harris & Chen, 2015), Co-Fe-X (X = Ga, Al, Si, Ge) (Wurmehl et al, 2005;Balke et al, 2007Balke et al, , 2008Wang et al, 2010;Wang, Casper, Guo et al, 2012;Liang et al, 2016;Patra et al, 2018Patra et al, , 2019aHusain et al, 2019) and Co-Mn-X (X = Si, Ge) (Zschech et al, 1984;Ravel et al, 2002;Ouardi et al, 2011). XAS techniques have also successfully been applied to the study of quaternary alloys, like Co-Cr-Fe-X (X = Al, Si) (Wurmehl et al, 2006(Wurmehl et al, , 2007Rani et al, 2018), Co-Fe-Mn-X (X = Si, Ge) (Bainsla et al, 2015), Co-Rh-Mn-Ge (Rani et al, 2017), Ni-Mn-In-Fe (Lobo et al, 2014), Cu-Ni-Mn-Sb (Bandyopadhyay et al, 2018 and Fe-Mn-Cu-Al (Nanto et al, 2014).…”

Reversible tuning of magnetocaloric Ni-Mn-Ga-Co films on ferroelectric PMN-PT substrates

“…Though this is low compared to the spontaneous strain of about 22 % occurring during the martensitic transition from austenite to non-modulated martensite, the same underlying mechanics may be relevant. For a complete metamagnetic transition, this spontaneous strain changes magnetisation by 100 %, which is commonly attributed to the Mn atoms being at an interatomic distance close to the crossover from ferromagnetic to antiferromagnetic coupling 35 – 37 . We propose that the high sensitivity of magnetism on the interatomic distances is also the underlying mechanism for the observed reversible change of magnetisation by 7 % at a biaxial in-plane compression of about 0.1 %.…”

Evidence of Change in the Density of States during the Martensitic Phase Transformation of Ni-Mn-In Metamagnetic Shape Memory Alloys

“…The specimen with x = 0 (NiMn) has been reported to be collinear-type antiferromagnetic with the Néel temperature higher than the martensitic transformation temperature [15]. Therefore, the magnetic state is deduced to be antiferromagnetic for low In concentrations, and the antiferromagnetic exchange interaction in the system decreases with increasing In content [16,17]. The NiMn has an L1 0 -type tetragonal structure with lattice parameters of a = 0.374 and c = 0.352 nm, and it transforms to B2-type cubic one at the martensitic transformation temperature [15].…”