Large magnetoresistance in current-perpendicular-to-plane pseudospin valve using a Co2Fe(Ge0.5Ga0.5) Heusler alloy
TL;DR: Using a newly developed highly spin-polarized Heusler alloy, Co2Fe(Ga05Ge05) (CFGG), as ferromagnetic layers, a current-perpendicular-to-plane pseudospin valve with large resistance change-area product (ΔRA) of 95mΩμm2 and magnetoresistance (MR) ratio (100×ΔR/R) of 417% at 300 K were fabricated in this paper.
Abstract: Using a newly developed highly spin-polarized Heusler alloy, Co2Fe(Ga05Ge05) (CFGG), as ferromagnetic layers, we have fabricated a current-perpendicular-to-plane pseudospin valve with large resistance change-area product (ΔRA) of 95 mΩ μm2 and magnetoresistance (MR) ratio (100×ΔR/R) of 417% at 300 K These values were further enhanced to ΔRA=264 mΩ μm2 and MR=1291% at 10 K The large MR values are attributed to the high spin polarization of the CFGG alloy confirmed by point contact Andreev reflection measurements
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TL;DR: In this article, the authors investigated 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.
Abstract: 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.
224 citations
TL;DR: In this article, a fully epitaxial Co2FexMn1−xSi(CFMS)/Ag/Co2FExMn 1−x Si current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses tCFMS were prepared.
Abstract: Fully epitaxial Co2FexMn1−xSi(CFMS)/Ag/Co2FexMn1−xSi current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses tCFMS were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x = 0.4 and tCFMS = 3 nm. Enhancement of interface spin-asymmetry was suggested for x = 0.4 compared with that at x = 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives.
151 citations
TL;DR: Heusler alloys are theoretically predicted to become half-metals at room temperature (RT) and by employing these ferromagnetic alloy films in a spintronic device, efficient spin injection into a non-magnetic material and large magnetoresistance are also discussed.
126 citations
TL;DR: The spin polarization of ferromagnetic Heusler alloys, Co 2 Fe(Ga x Ge 1−x ) ( x ǫ = 0, 0.75, and 1), is investigated by point contact Andreev reflection (PCAR) measurements as discussed by the authors.
105 citations
TL;DR: In this article, a fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) with a Co2Fe0.4Mn0.6Si structure was fabricated.
Abstract: Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with a Co2Fe0.4Mn0.6Si/Ag/Co2Fe0.4Mn0.6Si structure were fabricated. The bottom and top Co2Fe0.4Mn0.6Si layers had good crystallinity and an L21-ordered structure. In addition, we found from scanning transmission electron microscopy (STEM) measurements that both Co2Fe0.4Mn0.6Si/Ag and Ag/Co2Fe0.4Mn0.6Si interfaces were very flat and sharp. The magnetoresistance (MR) ratio at room temperature was 74.8%, the largest to date for CPP-GMR devices. CPP-GMR devices with Co2Fe0.4Mn0.6Si electrodes would be very useful for the next generation of hard disk drive (HDD) read heads.
98 citations
References
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TL;DR: In this article, the full-potential screened Korringa-Kohn-Rostoker method was used to study the half-metallic properties of Co, Fe, Rh, and Ru.
Abstract: Using the full-potential screened Korringa-Kohn-Rostoker method we study the full-Heusler alloys based on Co, Fe, Rh, and Ru. We show that many of these compounds show a half-metallic behavior; however, in contrast to the half-Heusler alloys the energy gap in the minority band is extremely small due to states localized only at the Co (Fe, Rh, or Ru) sites which are not present in the half-Heusler compounds. The full-Heusler alloys show a Slater-Pauling behavior and the total spin magnetic moment per unit cell ${(M}_{t})$ scales with the total number of valence electrons ${(Z}_{t})$ following the rule ${M}_{t}{=Z}_{t}\ensuremath{-}24.$ We explain why the spin-down band contains exactly 12 electrons using arguments based on group theory and show that this rule holds also for compounds with less than 24 valence electrons. Finally we discuss the deviations from this rule and the differences compared to the half-Heusler alloys.
1,688 citations
TL;DR: A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermani surface.
Abstract: A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals. Because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermi surface, the differential conductance of the point contact can reveal the spin polarization of the metal. This technique has been applied to a variety of metals where the spin polarization ranges from 35 to 90 percent: Ni0.8Fe0.2, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2.
1,469 citations
TL;DR: In this paper, the mechanisms of the giant magnetoresistance (MR) in magnetic multilayers were discussed very generally for both the CIP (current in plane) and CPP (current perpendicular to the planes) geometries.
Abstract: In the talk presented by one of us (AF) at Cargese, the mechanisms of the giant magnetoresistance (MR) in magnetic multilayers were discussed very generally for both the CIP (current in plane) and CPP (current perpendicular to the planes) geometries. A so general discussion would be too long for these proceedings and the present paper will be restricted to the CPP case. We present the theoretical model that we have recently worked out [1,2] and discuss its application to experimental data obtained for the Ag/Co and Cu/Co systems at Michigan State University [3,4,5] and presented at Cargese by Pr. P.A. Schroeder [6]. We describe the specific fundamental problems related to the spin accumulation effects occuring in the CPP geometry and we calculate the magnetoresistance. The expressions of the MR become relatively simple in the limit where the layer thicknesses are much smaller than the spin diffusion length and we justify the analysis of experimental results developed at Michigan State University [3–6]. We also relate our theory to those of Johnson et al [7,8], van Son et al [9] and Zhang and Levy [10]. Of course, it is not in the scope of the present paper to develop calculations presented elsewhere in detail [1] and we will focus on the presentation of the basis of the model and the discussion of our results.
1,357 citations
TL;DR: In this article, a general method for the calculation of lattice constants from powder photographs is given, in which there is taken into account the various systematic errors inevitable in such photographs, including radius errors, film shrinkage, absorption, eccentricity and finite slit height.
Abstract: A very general method is given for the calculation of lattice constants from powder photographs in which there is taken into account the various systematic errors inevitable in such photographs, including radius errors, film shrinkage, absorption, eccentricity and finite slit height. While the solution of the data is made by least squares, it is not at all laborious and is much simpler than the various methods, both analytical and graphical, which have previously been proposed. Examples are given of cubic, hexagonal and orthorhombic structures solved in this way using data from Debye and focusing cameras, extension to other structures and cameras being made evident. In effect, powder cameras become absolute instruments, independent of calibrating substances, and dependent only on the value of the x‐ray wavelength.
417 citations
TL;DR: In this paper, point-contact Andreev reflection measurements of point contact point contacts were analyzed with the Blonder-Tinkham-Klapwijk theory extended to include the polarization P of the metal and proximity effects.
Abstract: We present point-contact Andreev reflection measurements of $X/\mathrm{N}\mathrm{b}$ contacts, where $X=\mathrm{Ni},$ Co, Fe, and Cu. Experimental conductance-voltage curves were analyzed with the Blonder-Tinkham-Klapwijk theory [Phys. Rev. B 25, 4515 (1982)], extended to include the polarization P of the metal and proximity effects. For Ni, Co, and Fe the conductance-voltage curves can be well described by the model with P and Z as the fitting parameters, where Z is a dimensionless barrier strength included in the model to describe elastic scattering at a nonideal metal/superconductor interface. The polarization for Fe, Co, and Ni depends on the magnitude of Z. The value of the intrinsic P can be obtained by extrapolation to $Z=0$ (perfectly transparent interface). For Cu, the conductance-voltage curves show a dip at the position of the Nb superconducting gap, due to proximity effects, which reduce the effective gap value for the normal to supercurrent conversion at the Cu/Nb interface, while leaving the gap for quasiparticle transport essentially unchanged. In addition, an overall decrease of the gap is observed when the size of the point contact approaches the superconducting coherence length in Nb. We have included these effects in our model and obtained very good agreement between experimental data and model calculations.
250 citations