Development of antiferromagnetic Heusler alloys for the replacement of iridium as a critically raw material

Abstract

As a platinum group metal, iridium (Ir) is the scarcest element on the earth but it has been widely used as an antiferromagnetic layer in magnetic recording, crucibles and spark plugs due to its high melting point. In magnetic recording, antiferromagnetic layers have been used to pin its neighbouring ferromagnetic layer in a spin-valve read head in a hard disk drive for example. Recently, antiferromagnetic layers have also been found to induce a spin-polarised electrical current. In these devices, the most commonly used antiferromagnet is an Ir–Mn alloy because of its corrosion resistance and the reliable magnetic pinning of adjacent ferromagnetic layers. It is therefore crucial to explore new antiferromagnetic materials without critical raw materials. In this review, recent research on new antiferromagnetic Heusler alloys and their exchange interactions along the plane normal is discussed. These new antiferromagnets are characterised by very sensitive magnetic and electrical measurement techniques recently developed to determine their characteristic temperatures together with atomic structural analysis. Mn-based alloys and compounds are found to be most promising based on their robustness against atomic disordering and large pinning strength up to 1.4 kOe, which is comparable with that for Ir–Mn. The search for new antiferromagnetic films and their characterisation are useful for further miniaturisation and development of spintronic devices in a sustainable manner.

Magnetism and exchange-bias effect at the MnN/Fe interface

“…FeMn and NiMn are known alternatives that also produce an EB effect, but the ratios of the exchange bias to the coercive fields are less ideal for technological applications [14]. Because of this technological relevance, the quest for new antiferromagnetic materials avoiding scarce elements is an important topic of modern material research [16], and, in a recent work of Meinert et al [17], it was shown that in the case of polycrystalline MnN/CoFe interfaces a strong exchange-bias effect exists. Although this material combination displays a nonmonotonic dependence of the EB field on both the AF and FM thicknesses, this work indicates the possibility to use MnN as antiferromagnetic material in future magnetic devices.…”

Distinct impact of order degree on thermoelectric power factor of p-type full-Heusler Mn2VAl compounds

“…Mn 2 VAl is a ferrimagnetic compound below ∼767 K, above which it transforms to a paramagnetic phase [19]. These magnetic properties are not significantly affected by the order degree in the case that Mn 2 VAl is in a L2 1 or B2 structure, because calculated exchange parameters are similar between the two structures [30]. On the other hand, we found no obvious difference between the measured Seebeck coefficients in the heating process and the cooling process within the error range (not shown here).…”

Unusual perpendicular anisotropy in Co2TiSi films

“…This type of anisotropy arises in magnets where a = b = c but the arrangement of the atoms inside the unit cells breaks the cubic symmetry. Experimentally well-investigated examples are L1 0 magnets such as FePt and CoPt, where a = b ≈ c [31,39,40] and a small strain can be used to realize c/a = 1 without substantial change in the high magnetic anisotropy. Pseudocubic anisotropy has not been observed yet in Heusler alloy, although the B2 structures theoretically investigated by Hirohata et al [40] contain a superstructure ( Figure 12 in [40]) and may therefore be classified as pseudocubic magnets.…”