Heusler alloys for spintronic devices: review on recent development and future perspectives

Abstract

Heusler alloys are theoretically predicted to become half-metals at room temperature (RT). The advantages of using these alloys are good lattice matching with major substrates, high Curie temperature above RT and intermetallic controllability for spin density of states at the Fermi energy level. The alloys are categorised into half- and full-Heusler alloys depending upon the crystalline structures, each being discussed both experimentally and theoretically. Fundamental properties of ferromagnetic Heusler alloys are described. Both structural and magnetic characterisations on an atomic scale are typically carried out in order to prove the half-metallicity at RT. Atomic ordering in the films is directly observed by X-ray diffraction and is also indirectly probed via the temperature dependence of electrical resistivity. Element specific magnetic moments and spin polarisation of the Heusler alloy films are directly measured using X-ray magnetic circular dichroism and Andreev reflection, respectively. By employing these ferromagnetic alloy films in a spintronic device, efficient spin injection into a non-magnetic material and large magnetoresistance are also discussed. Fundamental properties of antiferromagnetic Heusler alloys are then described. Both structural and magnetic characterisations on an atomic scale are shown. Atomic ordering in the Heusler alloy films is indirectly measured by the temperature dependence of electrical resistivity. Antiferromagnetic configurations are directly imaged by X-ray magnetic linear dichroism and polarised neutron reflection. The applications of the antiferromagnetic Heusler alloy films are also explained. The other non-magnetic Heusler alloys are listed. A brief summary is provided at the end of this review.

Perpendicular Anisotropy Controlled by Seed and Capping Layers of Heusler-Alloy Films

“…In W, there is an almost twofold increase in the crystallite size from 5.4 nm ± 0.2 nm to 9.2 nm ± 0.1 nm associated with the increased crystallinity. CFAS without heating shows noncrystalline or nanocrystalline nature as expected [3]. In the samples grown at 62 • C, on the other hand, a crystallite size of 7.9 nm ± 0.1 nm is obtained.…”

“…H EUSLER alloys have been investigated intensively due to their half-metallicity at room temperature, which is considered an ideal spin source for spintronic devices [1]- [3]. The alloys can also exhibit other magnetism by controlling the number of valence band electrons in the alloys and the associated magnetic interactions, achieving antiferromagnetism [4], ferrimagnetism [5], topological insulator [6], and spin gapless semiconductor [7].…”

A Comparative Study of Spin Magnetic Moment, Spin Polarization and Curie Temperature of Heusler type Compounds (A_2-X-YZ_y)Mnz (A = Ni, Pd, Pt And Z = Sb, Sn)

“…In 1983, de Groot and his coworkers (de Groot et al, 1983(de Groot et al, , 1984 had shown in their revolutionary studies that these materials belong to a novel class half metal, which has been since then investigated rigorously. By this time, some other interesting properties of Heusler compounds have been pointed out by different research groups (Elphick et al, 2021;Yu et al, 2015;Wu et al, 2020).…”

Growth and Characterisation of Antiferromagnetic Ni2MnAl Heusler Alloy Films

“…The (220) peaks were used to quantify the A2 crystalline ordering (atomic mixing between Ni, Mn and Al), i.e., the increase in Q factor represents the increase in A2 ordering, which typically leads to B2 ordering (atomic mixing between Ni and Mn) with a coexisting (200) peak and L2 1 perfect ordering with coexisting (200) and (111) peaks [12].…”