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Frustrated magnetism of the maple-leaf-lattice antiferromagnet MgMn3O7·3H2O

Yuya Haraguchi, Akira Matsuo, Koichi Kindo, and Zenji Hiroi
Phys. Rev. B 98, 064412 – Published 13 August 2018
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  • INTRODUCTION
  • EXPERIMENTS
  • RESULTS
  • DISCUSSION
  • SUMMARY
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We present the novel hydrated layered manganate MgMn3O7·3H2O as a maple-leaf-lattice (MLL) antiferromagnet candidate. The MLL is obtained by regularly depleting 1/7 of the lattice points from a triangular lattice so that the magnetic connectivity z=5 and is thus intermediately frustrated between the triangular (z=6) and kagome (z=4) lattices. In MgMn3O7·3H2O, the Mn4+ ions carrying Heisenberg spin 3/2 form a regular MLL lattice in the quasi-two-dimensional structure. Magnetization and heat capacity measurements using a hydrothermally prepared powder sample reveal successive antiferromagnetic transitions at 5 and 15 K. A high-field magnetization curve up to 60 T at 1.3 K exhibits a multistep plateaulike anomaly. We discuss the unique frustration of the MLL antiferromagnet in which the chiral degree of freedom may play an important role.

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    • Received 20 June 2018

    DOI:https://doi.org/10.1103/PhysRevB.98.064412

    ©2018 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    AntiferromagnetismFrustrated magnetismMagnetic susceptibilitySpin state transition
    1. Physical Systems
    AntiferromagnetsMagnetic insulatorsPolycrystalline materials
    1. Techniques
    Magnetization measurementsSpecific heat measurements
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Yuya Haraguchi*, Akira Matsuo, Koichi Kindo, and Zenji Hiroi

    • The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan

    • *chiyuya@issp.u-tokyo.ac.jp

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    Issue

    Vol. 98, Iss. 6 — 1 August 2018

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    • Figure 1
      Figure 1

      Comparison between three geometrically frustrated lattices in two dimensions: (a) triangular, (b) maple-leaf, and (c) kagome lattices. Here, d is the amount of depletion from the triangular lattice, and z is the magnetic connectivity for each lattice.

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    • Figure 2
      Figure 2

      Magnetic network with the three kinds of magnetic interactions, Jd,Jt, and Jh, in the maple-leaf-lattice antiferromagnet. The yellow arrows represent the spin arrangement expected in the case of Jd=Jt=Jh [6, 7], which may not be realized in actual magnets with nonequivalent interactions.

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    • Figure 3
      Figure 3

      (a) XRD pattern of a powder sample of MgMn3O7·3H2O. Crystal structures of MgMn3O7·3H2O viewed along (b) the c axis and (c) the ab plane. (d) Local atomic arrangements around the Mn ions with three nonequivalent magnetic interactions, Jd,Jt, and Jh. (e) Mn-O-Mn angle versus the Mn-Mn distance for the three magnetic interactions. The two different Mn-O-Mn angles for Jt(Jh) correspond to the two superexchange pathways via the Mn-O1-Mn and Mn-O3-Mn (Mn-O1-Mn and Mn-O2-Mn) bonds.

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    • Figure 4
      Figure 4

      Temperature dependence of magnetic susceptibility M/H and its inverse for MgMn3O7·3H2O under a magnetic field of 1 T. The solid line on the inverse susceptibility indicates the result of Curie-Weiss fitting.

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    • Figure 5
      Figure 5

      (a) Temperature dependences of M/H measured for several magnetic fields. In each field, measurements were conducted upon heating after zero-field cooling and then upon cooling, as shown by the arrows. (b) Temperature dependences of the real part of the ac susceptibility measured in oscillating magnetic fields of Hac=5Oe at frequencies of 0.1, 1, 10, and 100 Hz.

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    • Figure 6
      Figure 6

      (a) Isothermal magnetization curves measured at 50, 4.2, and 1.8 K for MgMn3O7·3H2O. The inset shows an enlarged view approaching 0 T. (b) Temperature dependence of the spontaneous magnetization Msp. The inset shows differences in the magnetization between the down- and upsweep curves Mdown−Mup.

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    • Figure 7
      Figure 7

      Temperature dependence of the heat capacity divided by temperature C/T for MgMn3O7·3H2O. The dashed line represents the lattice contribution estimated by fitting the data above 100 K, as described in the text. The inset shows C/T data at μ0H=0, 7, and 10 T. The magnetic entropy SM is shown in the bottom panel.

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    • Figure 8
      Figure 8

      Magnetization curves M−H and their derivatives measured in pulsed fields up to 60 T at 1.3 and 4.2 K for MgMn3O7·3H2O. The open circles below 7 T are measured in static fields, which are used to calibrate the high-field data. The vertical dashed lines represent the local minimum point of dM/dH, indicating the presence of magnetization plateaus. The horizontal lines indicate the value of approximately 3/8, 1/2, and 3/4 magnetization saturation. The arrows indicate the critical fields.

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    • Figure 9
      Figure 9

      Possible magnetic structures for the MLL antiferromagnet in the case where |Jd|≫|Jt|>|Jh|: (a) SVC2, (b) PVC, and (c) NVC orders. The + and − symbols on each triangle represent the up and down vector chiralities, respectively.

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    • Figure 10
      Figure 10

      (a) MLL lattice with Jd,Jt, and Jh. (b) Jd dimers on the MLL forming a kagome lattice. (c) MLL in the limit where Jh→0. (d) Star lattice. The lattices in (c) and (d) are topologically equivalent.

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