Magnetic phase separation and exchange bias in off-stoichiometric Ni-Mn-Ga alloys

Abstract

The magnetic phase separation and exchange bias effect in off-stoichiometric Ni2Mn1.4Ga0.6 alloy were reported. Spontaneous exchange bias after zero-field cooling was observed in this alloy. The magnetic nature of ground state was characterized as phase separation with non-percolated ferromagnetic domains in spin glass matrix due to the spatial composition fluctuation and competing ferromagnetic and antiferromagnetic interactions. A mechanism of field-induced growth of ferromagnetic domains changing from non-percolating to percolating state was proposed for the appearance of spontaneous exchange bias.

Transformation of epitaxial NiMnGa/InGaAs nanomembranes grown on GaAs substrates into freestanding microtubes

“…The ZFC-FC irreversibility found in this work is consistent with reports on polycrystalline Ni 50 Mn 35 Ga 15 samples with tetragonal structure. 39,40 Similar to aforementioned mentioned works no martensitic transformations can be seen in the magnetization curves due to the nanocrystalline nature.…”

Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

“…The multifunctional properties usually appear across a martensitic transformation due to the strong coupling of crystal structure and magnetic order. The shape memory effect and magnetic-field-induced strains [6][7][8][9][10]12], superelasticity [13][14][15], magnetocaloric effect [16][17][18][19], as well as the spin glass and strain glass behavior [20][21][22][23] are found among these multifunctional properties. Generally, the tuning of both, structural and magnetic transition temperatures, can be useful to achieve better functional properties.…”

Exchange bias phenomena in Ni2−xMn1.4+xGa0.6

“…A simple and useful criterion to determine whether the observed frequency dependence in the ac susceptibility data is associated with metallic spin glass or not is to evaluate the values of the empirical relation, Φ = Δܶ [ܶ Δ݈‫݃‬ ଵ ݂] ିଵ , where Φ represents the relative shift of T p with f. 11,19,20,21 For metallic spin-glass systems the value typically lies between 0.005 and 0.01. A value greater than 0.01 and up to 0.04 would typically signify a SSG state.…”

“…4,5 Recently, EB has been reported in several bulk polycrystalline materials including a series of Mn rich Ni 2 Mn 1+x Z 1-x (Z = Ga, In, Sn, Sb) Heusler alloys. 6,7,8,9,10,11 These Heusler alloys exhibit a first order magnetostructural phase transition during which the high temperature L 21 cubic phase (austenite) transforms to a non-cubic lower symmetry martensitic phase at lower temperatures. The EB in the Mn-rich Huesler alloys is generally observed in the martensitic phase where the Mn-Mn exchange interaction within the regular Mn sublattices is ferromagnetic (FM), while the excess Mn atoms occupying the Z sites couple antiferromagnetically with the Mn atoms on the regular sites.…”

“…The decrease of magnetization in Ni 2-x Mn 1.4+x Ga 0.6 with increasing Mn for x > 0.15 may be attributed to similar reasons.The EB in Heusler alloys is often attributed to a frustrated or spin glass type nature of the ground state. We have performed ac susceptibility measurements on the Ni 2-x Mn 1.4+x Ga 0.6 samples in order to explore possible explanations behind the observed EB phenomena in the system 9,11,19. InFig.…”