A magnetoresistive element according to an embodiment includes: a first ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a second ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to a film plane; a nonmagnetic layer placed between the first ferromagnetic layer and the second ferromagnetic layer; a first interfacial magnetic layer placed between the first ferromagnetic layer and the nonmagnetic layer; and a second interfacial magnetic layer placed between the second ferromagnetic layer and the nonmagnetic layer The first interfacial magnetic layer includes a first interfacial magnetic film, a second interfacial magnetic film placed between the first interfacial magnetic film and the nonmagnetic layer and having a different composition from that of the first interfacial magnetic film, and a first nonmagnetic film placed between the first interfacial magnetic film and the second interfacial magnetic film

Magnetoresistive element and magnetic memory

We employ ab-initio electronic structure calculations to study 60 LiMgPdSn-type (also known as LiMgPdSb-type) quaternary Heusler compounds. All compounds obey the Slater-Pauling rule with diverse electronic and magnetic properties. 41 compounds are found to be half-metals, 8 spin-gapless semiconductors, and 9 semiconductors. CoVTiAl and CrVTiAl compounds are identified as ferromagnetic and antiferromagnetic semiconductors, respectively, with large energy gaps in both spin directions. All magnetic compounds are expected to have high Curie temperatures making them suitable for spintronics/magnetoelectronics applications.

/pdf/slater-pauling-behavior-in-limgpdsn-type-multifunctional-2raj2np9r9.pdf

Slater-Pauling behavior in LiMgPdSn-type multifunctional quaternary Heusler materials: Half-metallicity, spin-gapless and magnetic semiconductors

Large half-metallic gaps in the quaternary Heusler alloys CoFeCrZ (Z = Al, Si, Ga, Ge): A first-principles study

The authors investigate the properties of 378 half-Heusler compounds using density functional theory with the goal of identifying promising candidates for spintronic applications, e.g. half-metals. Although DFT has often been applied to the search for half-metals, this study may be the most comprehensive attempt to identify which of the compounds predicted by DFT to be half-metals are likely to be fabricated. The calculated formation energy of each of the 378 potential half Heuslers was compared to that of all competing phases and combination of phases in the Open Quantum Materials Database. Those semiconductors, half-metals, and near half-metals within an empirically determined 0.1 eV/atom hull distance margin for neglected effects were deemed of interest for further experimental investigation.

Computational investigation of half-Heusler compounds for spintronics applications

Half-metallic ferromagnetic (HMF) materials show high spin polarization and are therefore interesting to researchers due to their possible applications in spintronic devices. In these materials, while one spin sub band has a finite density of states at the Fermi level, the other sub band has a gap. Because of their high Curie temperature (TC) and tunable electronic structure, HMF Heusler alloys have a special importance among the HMF materials. Full Heusler alloys with the stoichiometric composition X2YZ (where X and Y are the transition metals and Z is a sp element) have the cubic L21 structure with four interpenetrating fcc sublattices. When each of these four fcc sublattices is occupied by different atoms (XX′YZ), a quaternary Heusler structure with different structural symmetries (space group F-43m, #216) is obtained. Recently, these equiatomic quaternary Heusler alloys (EQHAs) with 1:1:1:1 stoichiometry have attracted a lot of attention due to their superior magnetic and transport properties. A speci...

Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

This work reports on three quaternary Heusler compounds NiFeMnGa, NiCoMnGa, and CuCoMnGa. In contrast to their ternary relatives, quaternary Heusler compounds are still rarely investigated. A very large pool of interesting materials lies thus idle waiting for exploration. The difficulty consists in choosing prospective compositions, and trial and error is elaborate and expensive. We have identified several candidates employing ab initioelectronic-structure calculations. The compounds were synthesized, and the structural and magnetic properties were investigated experimentally. CuCoMnGa is a quaternary Heusler compound; NiFeMnGa and NiCoMnGa are unreported half-metallic ferromagnetic materials with potential for spintronics applications.

Quaternary half-metallic Heusler ferromagnets for spintronics applications

The magnetic properties of Mn3−xCoxGa Heusler alloys exhibit a very interesting feature. While the Mn-rich alloys (x = 0.1−0.4) are similar to Mn3Ga as they crystallize in a tetragonally distorted variation of the Heusler structure and exhibit comparable hard-ferrimagnetic properties highly useful for spin-transfer torque applications, the Co-rich samples (x = 0.6–1) exhibit cubic Heusler structures, have soft-magnetic hysteresis loops, and follow the generalized Slater-Pauling curve indicating half-metallic ferrimagnetism. The Curie temperatures of all alloys are above 700 K allowing for high operating temperatures.

Tuning the magnetism of the Heusler alloys Mn3−xCoxGa from soft and half-metallic to hard-magnetic for spin-transfer torque applications

Within the huge family of Heusler compounds only a few quaternary derivatives are known that crystallize in the space group. In this work, the yet unreported compounds CoRhMnZ (Z = Ga, Sn, Sb) and the alloy Co0.5Rh1.5MnSb were investigated in detail by experimental techniques and theoretical methods. The ab initio calculations predict the CoRhMnZ compounds to be half-metallic ferromagnets or to be close to the half-metallic ferromagnetic state. Calculations of the elastic constants show that the cubic structure is stable in compounds containing Mn. Both calculations and experiment reveal that Mn cannot be exchanged by Fe (CoRhFeGa). The low temperature magnetization of the compounds is in the range of 3.4–5.5 μB depending on the composition. The best agreement between experiment and calculation has been achieved for CoRhMnSn (5 μB). The other compounds are also cubic but tend to anti-site disorder. Compared to Co2MnSn it is interesting to note that the magnetic properties and half-metallicity are preserved when replacing one of the ‘magnetic’ Co atoms by a ‘non-magnetic’ Rh atom. This allows us to increase the spin–orbit interaction at one of the lattice sites while keeping the properties as a precondition for applications and physical effects relying on a large spin–orbit interaction. The Curie temperatures were determined from measurements in induction fields of up to 1 T by applying molecular field fits respecting the applied field. The highest Curie temperature was found for CoRhMnSn (620 K) that makes it, together with the other well defined properties, attractive for above room temperature spintronic applications.

http://iopscience.iop.org/article/10.1088/0953-8984/24/4/046001/pdf

Quaternary Heusler compounds Co2−xRhxMnZ (Z = Ga, Sn, Sb): crystal structure, electronic structure, and magnetic properties

The tetragonal Mn2RhSn Heusler compound shows better lattice match with MgO than do Mn3−xGa and tetragonal Mn3−xCoxGa Heusler compounds and hence is better suited for spin transfer torque applications. Beside the improved lattice match, this compound shows a low saturation magnetic moment reduces the current to switch which makes it more relevant for application in spin transfer torque devices. This compound shows a low Curie temperature; introducing Co into this system and increasing the Rh content leads to an increase in the Curie temperature. Doping with Co retains the tetragonal structure, with improved lattice match with MgO and low magnetic moment, intact up to x = 0.6, although doping with Rh changes the structure from tetragonal to cubic.

Juergen Winterlik

Papers

Quaternary half-metallic Heusler ferromagnets for spintronics applications

Tuning the magnetism of the Heusler alloys Mn3−xCoxGa from soft and half-metallic to hard-magnetic for spin-transfer torque applications

Quaternary Heusler compounds Co2−xRhxMnZ (Z = Ga, Sn, Sb): crystal structure, electronic structure, and magnetic properties

Increasing Curie temperature in tetragonal Mn2RhSn Heusler compound through substitution of Rh by Co and Mn by Rh