High-performance giant-magnetoresistance junctions based on the all-Heusler architecture with matched energy bands and Fermi surfaces

Significance Statement

Giant magnetoresistance (GMR) was discovered in 1988 by Albert Fert (France) and Peter Grünberg (Germany). The practical significance of this experimental discovery was recognized by the Nobel Prize in Physics awarded to Fert and Grünberg in 2007. Now, Giant magnetoresistance has been widely used in hard disk drives and magnetoresistive random-access memories. Giant magnetoresistance is a quantum mechanical magnetoresistance effect observed in thin-film structures composed of alternating ferromagnetic and non-magnetic conductive space layers. Traditional space layers are Cu or Ag, whose Fermi surface are poorly matched to that of the ferromagnetic leads, resulting a low MR efficiency. Here, we proposed all-Heusler Giant magnetoresistance devices with the ferromagnetic Heusler (Co₂MnSi) leads and non-magnetic conductive Heusler (Ni₂NiSi) spacer. Because of the matched energy bands and Fermi surfaces, all-Heusler Giant magnetoresistance devices show a superior Giant magnetoresistance performance.

Figure Legend Almost perfectly matched Fermi surfaces between the Co₂MnSi leads and Ni₂NiSi spacer, and high spin transmittance (upper panel). Poorly Fermi surfaces between the Co₂MnSi leads and Ag spacer, and relatively low spin transmittance (lower panel).

Journal Reference

Appl. Phys. Lett. 102, 152403 (2013).

Zhaoqiang Bai, Yongqing Cai, Lei Shen, Guchang Han, Yuanping Feng.

Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore and

Data Storage Institute, Agency for Science, Technology and Research, 5 Engineering Drive 1, Singapore 117608, Singapore

Abstract

We present an all-Heusler architecture which could be used as a rational design scheme for achieving high spin-filter efficiency in the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A Co₂MnSi/Ni₂NiSi/Co₂MnSi trilayer stack is chosen as the prototype of such an architecture, of which the electronic structure and magnetotransport properties are systematically investigated by first principles approaches. Well matched energy bands and Fermi surfaces between the all-Heusler electrode-spacer pair are found, which, in combination with the electrode half-metallicity, indicate large bulk and interfacial spin-asymmetry, high spin-filter efficiency, and consequently good magnetoresistance performance. Transport calculations further confirm the superiority of the all-Heusler architecture over the conventional Heusler/transition-metal structure by comparing their transmission coefficients and interfacial resistances of parallel conduction electrons, as well as the macroscopic current-voltage characteristics. We suggest future theoretical and experimental efforts in developing high-performance all-Heusler CPP-GMR junctions for the read heads of the next generation high-density hard disk drives.

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High-performance giant-magnetoresistance junctions based on the all-Heusler architecture with matched energy bands and Fermi surfaces

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