Abstract
For the sustainable development of spintronic devices, a half-metallic ferromagnetic film needs to be developed as a spin source with exhibiting 100% spin polarisation at its Fermi level at room temperature. One of the most promising candidates for such a film is a Heusler-alloy film, which has already been proven to achieve the half-metallicity in the bulk region of the film. The Heusler alloys have predominantly cubic crystalline structures with small magnetocrystalline anisotropy. In order to use these alloys in perpendicularly magnetised devices, which are advantageous over in-plane devices due to their scalability, lattice distortion is required by introducing atomic substitution and interfacial lattice mismatch. In this review, recent development in perpendicularly-magnetised Heusler-alloy films is overviewed and their magnetoresistive junctions are discussed. Especially, focus is given to binary Heusler alloys by replacing the second element in the ternary Heusler alloys with the third one, e.g., MnGa and MnGe, and to interfacially-induced anisotropy by attaching oxides and metals with different lattice constants to the Heusler alloys. These alloys can improve the performance of spintronic devices with higher recording capacity.
Highlights
IntroductionSince the discovery of giant magnetoresistance (GMR) by Fert [1] and Grünberg [2] independently, magnetoresistive (MR) junctions have been used widely in many spintronic devices [3,4], e.g., a read head in a hard disk drive (HDDs) [5], and a cell in a magnetic random access memory (MRAM) [6]
Since the discovery of giant magnetoresistance (GMR) by Fert [1] and Grünberg [2] independently, magnetoresistive (MR) junctions have been used widely in many spintronic devices [3,4], e.g., a read head in a hard disk drive (HDDs) [5], and a cell in a magnetic random access memory (MRAM) [6].The maximum GMR ratio achieved in a [Co (0.8)/Cu (0.83)]60 junction was reported to be 65% at 300 K [7]
In a Co0.5 Fe0.5 (2.5)/Al-nano2 oxide layers (NOL)/Co0.5 Fe0.5 (2.5) junction, resistancearea product (RA) = 0.5~1.5 Ω·μm2 and MR = 7~10% at room temperature (RT) has been achieved. These values are below the requirement for the 2 Tbit/in2 HDD, and further improvement in GMR or tunnelling magnetoresistance (TMR) junctions are crucial
Summary
Since the discovery of giant magnetoresistance (GMR) by Fert [1] and Grünberg [2] independently, magnetoresistive (MR) junctions have been used widely in many spintronic devices [3,4], e.g., a read head in a hard disk drive (HDDs) [5], and a cell in a magnetic random access memory (MRAM) [6]. For further improvement in HDD and MRAM, it is critical to satisfy two criteria: (i) low power consumption and resulting unfavourable side effects, such as Joule heating and possible damage resistance-area product (RA) and (ii) perpendicular magnetic anisotropy. Heusler alloys (red with circles) in-plane (open symbols) and perpendicular anisotropy symbols) together that with of giant magnetoresistive (GMR) junctions with 2 hard disk drive (HDD) read. Read heads as well as 1 and 10 Gbit magnetic random access memory (MRAM) applications are shown as purple and yellow respectively
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