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Enantiopurity-Controlled Magnetism in a Two-Dimensional Organic-Inorganic Material

P. Garrett Hegel, Oscar Gonzalez, Mingrui Li, Shannon S. Fender, Harishankar Jayakumar, Archana Raja, Ariana Ray, Isaac M. Craig, D. Kwabena Bediako

Abstract

Extended solids that combine unpaired electron spin and structural chirality can host unconventional magnetic behaviors with potential for electronic technologies. A versatile strategy for creating chiral solids is incorporation of chiral organic molecules into inorganic crystals. However, such hybrid organic-inorganic materials have so far been examined through the lens of absolute chirality, leaving enantiomeric excess (ee) underexplored as a tuning parameter. Here, we report two-dimensional (2D) intercalation compounds with controllable ee produced by cation exchange of MnPS$_3$ with chiral organic molecules. We show that these materials' magnetism is determined by intercalant ee rather than absolute chirality. Moreover, low-ee materials display thermally activated dynamic magnetism absent from enantiopure analogs. These ee-dependent magnetic behaviors are explained by local ordering of Mn vacancies, directed by correlated vacancy-intercalant electrostatics and confined molecular packing. Together, these results demonstrate a distinctive tuning strategy for molecule-material hybrids and establish design principles for 2D chiral and magnetically dynamic materials.

Enantiopurity-Controlled Magnetism in a Two-Dimensional Organic-Inorganic Material

Abstract

Extended solids that combine unpaired electron spin and structural chirality can host unconventional magnetic behaviors with potential for electronic technologies. A versatile strategy for creating chiral solids is incorporation of chiral organic molecules into inorganic crystals. However, such hybrid organic-inorganic materials have so far been examined through the lens of absolute chirality, leaving enantiomeric excess (ee) underexplored as a tuning parameter. Here, we report two-dimensional (2D) intercalation compounds with controllable ee produced by cation exchange of MnPS with chiral organic molecules. We show that these materials' magnetism is determined by intercalant ee rather than absolute chirality. Moreover, low-ee materials display thermally activated dynamic magnetism absent from enantiopure analogs. These ee-dependent magnetic behaviors are explained by local ordering of Mn vacancies, directed by correlated vacancy-intercalant electrostatics and confined molecular packing. Together, these results demonstrate a distinctive tuning strategy for molecule-material hybrids and establish design principles for 2D chiral and magnetically dynamic materials.

Paper Structure

This paper contains 22 sections, 5 figures.

Figures (5)

  • Figure 1: (a) Intercalation of chiral molecules into MnPS3. Purple, orange, and yellow spheres represent Mn, P, and S, respectively. (b) Powder X-ray diffraction patterns of pristine and intercalated powders. Data are normalized to the (001) reflection intensity for clarity. The intercalate (001) reflection is highlighted in gray. (c) IR spectra of pristine and intercalated powders. A spectrum of isolated [1-R][I] is included for reference. (d) Raman spectra of the pristine and intercalated powders. Modes involving Mn are highlighted in gray.
  • Figure 2: (a) Magnetic susceptibility as a function of temperature of the R, S, and rac intercalated samples measured at 100 Oe. (b) Representative magnetic hysteresis curves at 2 K for varying ee intercalates.
  • Figure 3: (a-b) Enantiopure and racemic intercalate magnetization as a function of applied field measured after aging under different storage conditions. (c) Racemic intercalate magnetization after thermal cycling. (d) Maximum magnetization at 0.5 T from (c) as a function of cycle number and cycling conditions. Blue shading denotes thermal cycles conducted under 300 K. (e-f) Racemic and enantiopure intercalate magnetization before and after a 12 hour 350 K heating and subsequent room temperature aging. All measurements are conducted at 2 K.
  • Figure 4: (a) The structure of hexagonally arranged Mn atoms within a single MnPS3 layer. (b) Top down spacefill model of intercalated molecules on a slab of MnPS3 with water molecules omitted. (c) Limiting cases of ferrimagnetically ordered Mn vacancies and evenly distributed, antiferromagnetic Mn vacancies after intercalation-induced removal of 1/6 Mn sites. (d) Possible ordered superlattices of Mn vacancies. Different net magnetizations are possible depending on the combination of superlattice cell and vacancy site(s).
  • Figure 5: Polarization dependence of SHG collected at room temperature from pristine and intercalated bulk crystals. Solid black lines are fits to the data.