Research ArticleMAGNETISM

Accelerated discovery of new magnets in the Heusler alloy family

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Science Advances  14 Apr 2017:
Vol. 3, no. 4, e1602241
DOI: 10.1126/sciadv.1602241
  • Fig. 1 Unit cells and phase stability of HAs.

    Possible HAs: (A) regular Heusler, (B) inverse Heusler, and (C) half Heusler. In (D), we show the unit cell used to construct the electronic structure database. (E) Ternary convex hull diagram for Al-Mn-Ni (note the presence of the stable HA, Ni2MnAl).

  • Fig. 2 Slater-Pauling curve for magnetic HAs of the Co2YZ form.

    (Left) Magnetic moment per formula unit, m, plotted against the number of valence electron, NV. (Right) TC. Red symbols correspond to predicted HAs, whereas black symbols correspond to existing materials. For clarity, several compounds were named collectively: Co2AB 1, Co2FeGa, Co2FeAl, Co2MnSi, Co2MnGe, and Co2MnSn; Co2AB 2, Co2TaAl, Co2ZrAl, Co2HfGa, Co2HfAl, and Co2TaGa; Co2AB 3, Co2ZrAl, Co2HfAl, Co2HfGa, and Co2TaGa.

  • Fig. 3 Critical temperature and magnetic moment for X2MnZ HAs.

    Magnetic data for X2MnZ magnets: TC (left) and magnetic moment per formula unit (right) as a function of the Mn-Mn distance, dMn-Mn. Note that the TC is limited to about 550 K and peaks at a volume of about 60 Å3. In contrast, the magnetic moment is approximately constant, with values in between 4 and 5 μB. Closed circles (with associated chemical compositions) correspond to the predicted compounds, whereas the other symbols correspond to experimental data. Different colors correspond to different number of valence electrons, NV. Blue chemical formulas correspond to compounds displaying tetragonal distortion. The two red lines denote Castelliz-Kanomata curves, whereas the black line is meant to guide the eye.

  • Fig. 4 Enthalpy of formation difference between the regular and inverse Heusler structure, ΔHRI, for Mn2-containing compounds as a function of the cell volume.

    The solid red squares (with chemical formulas) are the predicted stable intermetallic materials, whereas the open red squares are existing compounds. For completeness, we also include data for Co2-based HAs (open symbols, existing compounds; solid symbols, predicted compounds). In brackets beside the chemical formulas, we report the value for the entropic temperature, TS, in kelvin.

  • Fig. 5 Co2MnTi.

    (A) Magnetization curve at 4 and 300 K [inset: zero-field cooled (ZFC) magnetization curve as a function of temperature in a magnetic field of 1 T]. (B) XRD spectrum (inset: EDX chemical composition analysis). Co2MnTi crystallizes in a single Fmm phase corresponding to a regular Heusler. The TC extrapolated from the magnetization curve is around 900 K. arb. units, arbitrary units.

  • Fig. 6 Mn2PtPd.

    (A) Field cooled and zero-field cooled magnetization curves as a function of temperature in a magnetic field of 0.1 T (inset: magnetization curve at 4 and 300 K). (B) XRD spectrum (inset: EDX chemical composition analysis). Mn2PtPd crystallizes in a single I4/mmm (TiAl3-type) phase corresponding to a regular tetragonal distorted Heusler. SEM images confirm that the bulk sample is mainly of Mn2PtPd composition (gray color) with a small amount of secondary Mn-O inclusions, which have a spherical shape of 400 to 900 nm in diameter and do not appear in the XRD spectrum.

  • Table 1 Calculated properties of the 22 magnetic HAs found among all possible intermetallics.

    The table lists the unit cell volume of the F4¯3m cell, the c/a ratio for tetragonal cells (a), the Mn-Mn distance for Mn-containing alloys (dMn-Mn), the magnetic moment per formula unit (m), the spin polarization at the Fermi level (PF), the enthalpy of formation (ΔH), the entropic temperature (TS), and the magnetic ordering temperature (TC). Note that TC is evaluated only for Co2YZ and X2MnZ compounds for which a sufficiently large number of experimental data are available for other chemical compositions. In the case of Mn2YZ compounds, we report the magnetic moment of the ground state and, in brackets, that of the ferromagnetic solution. The last column provides a more stringent criterion of stability. Δ30 = Y if the given compound has an enthalpy within 30 meV/atom from that of its most favorable balanced decomposition (potentially decomposable), and Δ30 = N if this enthalpy is >30 meV/atom lower (robust). f.u., formula unit.

    AlloyV3)c/aa (Å)dMn-Mn (Å)mB/f.u.)PFΔH (eV/atom)TS (K)TC (K)Δ30
    Mn2PtRh58.566.163.080.00 (9.05)0.00 (0.86)−0.293247N
    Mn2PtCo54.286.003.001.13 (9.04)0.00 (0.86)−0.171918Y
    Mn2PtPd60.756.243.120.00 (8.86)0.00 (0.38)−0.293218N
    Mn2PtV55.736.063.034.87 (4.87)0.67−0.303353Y
    Mn2CoCr47.195.732.874.84 (4.84)0.02−0.05529N
    Co2MnTi49.685.844.920.58−0.283122940N
    Co2VZn46.875.731.010.93−0.151653228Y
    Co2NbZn*51.871.05.91.000.95−0.182034212Y
    Co2NbZn51.521.155.630.00.0−0.2020340Y
    Co2TaZn*51.801.05.920.980.63−0.222502125N
    Co2TaZn51.551.125.700.00.0−0.2325020N
    Rh2MnTi58.086.154.354.800.51−0.586500417Y
    Rh2MnZr64.506.374.504.750.34−0.586518338Y
    Rh2MnHf63.226.324.474.740.34−0.677474364Y
    Rh2MnSc61.626.274.434.310.77−0.637031429N
    Rh2MnZn54.956.034.273.370.63−0.313444372Y
    Pd2MnAu*64.211.06.364.494.600.06−0.202203853Y
    Pd2MnAu63.501.355.754.074.280.28−0.332203331Y
    Pd2MnCu57.636.134.344.530.06−0.222492415Y
    Pd2MnZn*58.881.06.174.374.330.38−0.394399894Y
    Pd2MnZn58.741.185.844.134.220.16−0.474399402Y
    Pt2MnZn*59.231.06.194.374.340.34−0.455035694Y
    Pt2MnZn58.951.225.794.104.130.02−0.655035381Y
    Ru2MnNb59.646.204.394.070.85−0.192068276Y
    Ru2MnTa59.726.204.394.060.86−0.262912305N
    Ru2MnV54.386.014.254.000.71−0.161832342Y
    Rh2FeZn54.606.024.240.49−0.283150N

    *Not stable against tetragonal distortion (Co2NbZn and Co2TaZn become diamagnetic after distortion).

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602241/DC1

      fig. S1. Magnetization curves for Mn2PtCo.

      fig. S2. Structural and chemical characterization of Mn2PtCo.

      fig. S3. Magnetization curves for Mn2PtV.

      fig. S4. Structural and chemical characterization of Mn2PtV.

      fig. S5. Histogram of the entropic temperature, TS, for all the 8776 intermetallic HAs displaying negative enthalpy of formation (ΔH < 0 and TS > 0).

      fig. S6. Histogram of the entropic temperature, TS, for all the 248 intermetallic HAs estimated stable after the construction of the convex hull diagrams for the ternary phase.

      fig. S7. Total energy as a function of the c/a ratio for Mn2PtPd calculated with GGA-DFT.

      References (3296)

    • Supplementary Materials

      This PDF file includes:

      • fig. S1. Magnetization curves for Mn2PtCo.
      • fig. S2. Structural and chemical characterization of Mn2PtCo.
      • fig. S3. Magnetization curves for Mn2PtV.
      • fig. S4. Structural and chemical characterization of Mn2PtV.
      • fig. S5. Histogram of the entropic temperature, TS, for all the 8776 intermetallic HAs displaying negative enthalpy of formation (ΔH < 0 and TS > 0).
      • fig. S6. Histogram of the entropic temperature, TS, for all the 248 intermetallic HAs estimated stable after the construction of the convex hull diagrams for the ternary phase.
      • fig. S7. Total energy as a function of the c/a ratio for Mn2PtPd calculated with GGA-DFT.
      • References (32–96)

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