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Intra-unitcell cluster-cluster magnetic compensation and large exchange bias in cubic alloys

Bimalesh Giri, Bhawna Sahni, C. Salazar Mejía, S. Chattopadhyay, Uli Zeitler, Aftab Alam, and Ajaya K. Nayak
Phys. Rev. B 104, 014413 – Published 13 July 2021
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  • INTRODUCTION
  • METHODS
  • THEORETICAL CALCULATION
  • STRUCTURAL ANALYSIS
  • MAGNETIZATION STUDY
  • TRANSPORT MEASUREMENT AND DISCUSSIONS
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    Composite quantum materials are the ideal examples of multifunctional systems, which simultaneously host more than one novel quantum phenomenon in physics. Here, we present a combined theoretical and experimental study to demonstrate the presence of an extremely large exchange bias in the range 0.8–2.7 T and a fully compensated magnetic state (FCF) in a special type of Pt and Ni-doped Mn3In cubic alloy. Here, oppositely aligned uncompensated moments in two different atomic clusters sum up to zero, which are responsible for the FCF state. Our density functional theory (DFT) calculations show the existence of several possible ferrimagnetic configurations with the FCF as the energetically most stable one. The microscopic origin of the large exchange bias can be interpreted in terms of the exchange interaction between the FCF background and the uncompensated ferrimagnetic clusters stabilized due to its negligible energy difference with respect to the FCF phase. We utilize pulsed magnetic field up to 60 T and 30 T static-field magnetization measurements to confirm the intrinsic nature of exchange bias in our system. Finally, our Hall effect measurements demonstrate the importance of uncompensated noncoplanar interfacial moments for the realization of large EB. The present finding of gigantic exchange bias in a unique compensated ferrimagnetic system opens up a direction for the design of novel quantum phenomena for the technological applications.

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    • Received 18 March 2021
    • Revised 28 June 2021
    • Accepted 1 July 2021

    DOI:https://doi.org/10.1103/PhysRevB.104.014413

    ©2021 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Exchange biasFerrimagnetismMagnetism
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Bimalesh Giri1,*, Bhawna Sahni2,*, C. Salazar Mejía3,*, S. Chattopadhyay3, Uli Zeitler4, Aftab Alam2,†, and Ajaya K. Nayak1,‡

    • 1School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni 752050, India
    • 2Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India
    • 3Dresden High Magnetic Field Laboratory (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
    • 4High Field Magnet Laboratory (HFML-EMFL), Radboud University, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands

    • *These authors contributed equally to this work.
    • †aftab@phy.iitb.ac.in
    • ‡ajaya@niser.ac.in

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    Vol. 104, Iss. 1 — 1 July 2021

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    Images

    • Figure 1
      Figure 1

      Decomposition of the Mn3In crystal structure. (a) Four Mn atoms (yellow spheres) forming an inner tetrahedron (IT). (b) Four Mn atoms (blue spheres) join together to form an inverted outer tetrahedron (OT), which is rotated by 30 degree with respect to the IT. (c) Six Mn atoms (magenta spheres) constituting an octahedron (OH) in a manner that makes each OH atom close to two IT and two OT atoms. (d) The IT, OT, and OH atoms caged inside the cuboctahedron (CO) formed by 12 Mn atoms (orange spheres). Altogether, this arrangement of IT+OT+OH+CO forms cluster-A. (e) Cluster-B is formed in a similar way to that of cluster-A. Here the CO is formed by 11 In atoms (light-green spheres) and one Mn atom (orange spheres), the OH is composed of four Mn atoms (magenta spheres) and two In atoms (light-green spheres). The atomic composition/geometry for the IT and OT remains same as of cluster-A. (f) Extended view of the complete unit cell of Mn3In with cluster-A centered at (0, 0, 0) and cluster-B at (0.5, 0.5, 0.5).

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    • Figure 2
      Figure 2

      Relative formation energy (ΔE) and net cell moments (μ) of 13 different ferrimagnetic (FiM) spin configurations for pure Mn3In. The exact arrangement of spin alignments at different Mn sublattices in each FiM configurations is shown in Table 1.

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    • Figure 3
      Figure 3

      Room-temperature powder x-ray diffraction (XRD) pattern along with Reitveld refinement for, [(a)–(c)] Mn3−xPtxIn (x=0.1 to 0.3) and [(d),(e)] Mn3−yNiyIn (y = 0.1 and 0.2). The experimentally observed intensity (IObs) and simulated intensity (ICal) data are represented by the black open circles and red solid lines, respectively. The solid lines in blue color describe the difference between the experimental and simulated intensity. The red vertical lines indicate the Bragg positions.

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    • Figure 4
      Figure 4

      (a) Temperature-dependent magnetization, M(T), measured at 0.1 T for Mn3−xPtxIn. Open (solid) symbols correspond to the ZFC (FC) data, respectively. The data for x=0.2 and x= 0.3 are multiplied by scaling factors of 1.3 and 1.5, respectively, for better visualization. Inset shows the Neel temperature TN vs x. (b) ZFC (open symbol) and +5T FC (solid symbol) M(H) loops measured at T= 2 K. M(H) loop corresponding to the sample x=0.2 and 0.3 are shifted by 0.6 and 1.2 μB/f.u., respectively, along the magnetization axis. (c) ZFC (open symbol), +5T FC (solid symbol) and −5 T FC (half-filled symbol) M(H) loops for Mn3−yNiyIn measured at T= 2 K. M(H) loop for y= 0.1 is shifted by −0.6 μB/f.u. The inset of (c) shows the M(T) curve; squares and circles represent data for y = 0.1 and y = 0.2, respectively.

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    • Figure 5
      Figure 5

      Pt concentration (x) dependent exchange bias fields (HEB) and coercive fields HC for Mn3−xPtxIn. Inset shows HEB and HC for Mn3−yNiyIn.

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    • Figure 6
      Figure 6

      (a) ZFC M(H) loops measured up to 60 T for Mn3−xPtxIn. Magnetization data for the sample x= 0.2 and 0.3 are shifted by 0.5 and 1.5 μB/f.u., respectively along M axis. (b) M(H) loops measured up to ±30T after field cooling the sample in an applied field of HFC = 15 T. M(H) loops of x= 0.2 and 0.3 are shifted by 0.8 and 1.6 μB/f.u., respectively.

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    • Figure 7
      Figure 7

      (a) Cluster-A and cluster-B with finite staggered magnetization aligned antiparallely. (b) Left panel: Fully compensated FiM background as a result of cancellation between the staggered magnetization of cluster-A (orange arrows) and cluster-B (magenta arrows). Right panel: Possible FiM cluster due to a finite net (cell) magnetic moment, as in FiM-6/FiM-10 configuration in Table 1. The dashed line indicates the interface between the FCF background and the FiM cluster with finite moment. (c) Field dependence of Hall resistivity (ρyx) measured at 5 K after field cooling the sample in an applied field of +7T (open circles) and −7T (open squares) for Mn2.8Ni0.2In. The open symbols represent experimental data while the solid lines correspond to the total calculated Hall resistivity. The schematic spin configuration at the top and bottom panels represent the possible interfacial FCF magnetic configuration at the field reversal point, which are marked in dotted circles and dotted squares, respectively. The solid angle subtended by the noncoplanar spins in the schematic diagrams are marked by shaded dark yellow region and the red arrows indicate the direction of fictitious magnetic field.

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