# Coexistence of room temperature magneto-chiral dichroism and magneto-electric coupling in a chiral nanomagnet

Langit Cahya Adi, Maxime Aragon-Alberti, Jérôme Rouquette, Geert L J A

Rikken, Cyrille Train, Jérôme Long, Matteo Atzori

► To cite this version:

Langit Cahya Adi, Maxime Aragon-Alberti, Jérôme Rouquette, Geert L J A Rikken, Cyrille Train, et al.. Coexistence of room temperature magneto-chiral dichroism and magneto-electric coupling in a chiral nanomagnet. Nanoscale, 2024, 17 (4), pp.1954-1958. 10.1039/d4nr04422c. hal-05375371

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# Coexistence of Room Temperature Magneto-Chiral Dichroism and Magneto-Electric Coupling in a Chiral Nanomagnet

Langit Cahya Adi,ª Maxime Aragon-Alberti,ª,b Jérôme Rouquette,ª Geert L.J.A. Rikken,ª Cyrille Train,ª Jérôme Long,ᵇ,c,\* Matteo Atzoriª,\*

Received 00th January 20xx,
Accepted 00th January 20xx

DOI: 10.1039/x0xx00000x

We report herein on the magneto-chiral dichroism (MChD), investigated through Near Infrared light absorption, of a chiral nanomagnet showing room temperature magneto-electric coupling. The MChD signal associated to the Yb¹¹¹ center is driven by the magnetic dipole allowed character of the ²F₇/₂ ← ²F₅/₂ electronic transition (|Δμ| = 1). Magnetic field and temperature dependence studies reveal a MChD signal that follows the material magnetization and persists at room temperature. These results represent the first evidence of coexistence between magneto-chiral dichroism and magneto-electric coupling at room temperature in a molecular nanomagnet and pave the way for further studies where magneto-chiral anisotropy and magneto-electric coupling would interact.

Magnetic materials responsive to external stimuli such as light irradiation or electric fields are of crucial importance for the development of new nanotechnologies.¹⁻⁴ Light irradiation can be used to induce magnetization changes with high spatial resolution and (ultra)fast timescales²,³ owing to specific light-matter interactions such as the Faraday or optical Kerr effects.⁵,⁶ Electric fields can be used to act on the materials magnetization much more locally than with magnetic fields on nanometer-size samples.⁴,⁷ This is achieved when the material’s magnetization is influenced by the electric field through magneto-electric coupling.⁷⁻⁹

Introducing structural chirality in molecular nanomaterials can help to achieve the above-mentioned interactions.¹⁰ For example, by breaking space-reversal symmetry, chirality combined with magnetic fields enable a magneto-chiral effect, called magneto-chiral dichroism (MChD).¹¹⁻¹³ MChD manifests as an enantioselective differential absorption of light shown by chiral magnetized media when a light wavevector **k** and a magnetic field **B** are applied collinearly to the sample.¹¹⁻¹⁴ This effect is similar to the Faraday effect⁶ but does not require light

polarization to be observed.¹⁵ Indeed, it has been recently demonstrated as an effective phenomenon to optically probe, using unpolarized light, the magnetic memories stored in chiral single-molecule magnets (SMMs), the smallest dimension nanoobjects able to retain magnetization.¹⁶

At the same time, structural chirality can drive the structural arrangement of magnetic molecular materials toward polar space groups which are compatible with ferroelectricity.⁸ In such systems, a spontaneous electrical polarization can appear and be switched by an electric field. When combined with magnetism, this can enable reciprocal control of magnetic and electric properties through magneto-electric coupling.⁷⁻⁹

Molecular materials exhibiting room temperature magneto-electric coupling are extremely rare. The best-known example is a chiral Zn¹¹¹/Yb¹¹¹-based complex that shows ferroelectricity at room temperature and strong magnetostriction.⁸ The association of the two phenomena is responsible for a distinctive magneto-electric coupling at room temperature demonstrated by piezoresponse force microscopy.⁸ Materials showing room temperature MChD are also uncommon.¹⁷ The few reported examples involve lanthanide chiral complexes¹⁸⁻²⁰ based on Yb¹¹¹, Er¹¹¹ or Tm¹¹¹ that are characterized by f-f transitions associated with a magnetic-dipole allowed character, a key-ingredient to observe strong MChD signals up to room temperature.¹⁸,¹⁹ Both effects are driven by the high angular momenta and strong spin-orbit coupling intrinsic to lanthanide ions, and are enabled by the space-symmetry breaking of structural chirality. However, to the best of our knowledge, no previous report has demonstrated the coexistence of magneto-electric coupling and magneto-chiral dichroism in a material. Potential effects of electric fields on chiral magnetic materials showing MChD are the modulation of the MChD response by acting i) on the electronic transitions selections rules¹⁹ or ii) the magnitude of the magnetization through magneto-electric coupling.⁷⁻⁹

In this work, we report the MChD investigation of the aforementioned Zn¹¹¹/Yb¹¹¹ complex.⁸ Notably, we demonstrate that MChD signals persist at room temperature, opening new avenues for exploring the interplay between magneto-electric coupling and MChD at ambient conditions.

<footnote>ª Laboratoire National des Champs Magnétiques Intenses (LNCMI), Univ. Grenoble Alpes, INSA Toulouse, Univ. Toulouse Paul Sabatier, EMFL, CNRS, Grenoble, France.</footnote>

<footnote>ᵇ Institut Charles Gerhardt Montpellier, UMR 5253, Université de Montpellier, ENSCM, CNRS, Place E. Bataillon, 34095 Montpellier Cedex 5, France.</footnote>

<footnote>ᶜ Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris - France.
Supplementary Information available: Additional figures and plots as mentioned in the text. See DOI: 10.1039/x0xx00000x</footnote>
Reaction of enantiopure chiral ligands with Zn(OAc)₂·2H₂O (OAc = acetate) and Yb(NO₃)₃·5H₂O provides enantiomerically pure compounds formulated as [ZnYb(R,R)-L(μ-OAc)(NO₃)₂] (1-(R,R)) and [ZnYb(S,S)-L(μ-OAc)(NO₃)₂] (1-(S,S)) where L stands for 2,2'-[[[(1S,2S)-1,2-diphenyl-1,2-ethanediyl]bis[(E)]nitrile methylidyne]bis[6-methoxy] or 2,2'-[[[(1R,2R)-1,2-diphenyl-1,2-ethanediyl]bis[(E)]nitrilemethylidyne]bis[6-methoxy].

The molecular and crystal structure of 1 has been previously described.⁸ Therefore, here we report only the most salient features. Compound 1 crystallizes in the polar and chiral space group P2₁. The unit cell content of 1-(R,R) is presented in Figure 1. It consists of two crystallographically independent complexes whose crystallographic differences are responsible for a net uncompensated dipolar moment along the b crystallographic axis.⁸

<figure><img src="image_2.png" /><figcaption>**Figure 1.** View of the content of the unit cell for 1, with the relative orientation of the two crystallographically independent molecules (gold and blue) with respect to the (0-, 1,1) crystallographic plane highlighted. The direction of the light wavevector and applied magnetic field during MChD measurements with respect to the unit cell is also shown. Colour code: pink, Yb; gray, Zn. Hydrogen atoms have been omitted for clarity.</figcaption></figure>

The Zn¹¹ ion is pentacoordinated by three oxygen and two nitrogen atoms in the inner ligand framework while Yb¹¹¹ has nine-coordination arrangement with four oxygens of two bidentate nitrate ligands, an oxygen from the acetate group, and four oxygen atoms from the chiral ligand. It should be highlighted that the carbon stereocenters of the chiral ligand are far from the Yb¹¹¹ ion and much closer to the Zn¹¹ ion, where they are directly involved in the asymmetric distortion of its coordination sphere.

The temperature dependence of the magnetic susceptibility times the temperature (χT vs T) was measured under an applied magnetic field *B* = 1.0 T on a microcrystalline sample of 1-(R,R) and the results shown in Figure S1. The data correspond well to an isolated Yb¹¹¹ ion per formula unit, and are well reproduced by *ab initio* calculation (*vide infra*). The magnetic field dependence of the magnetization at T = 4.0 K shows a typical unsaturated curve, with a value of 1.7 μB mol⁻¹ at 7.0 T (inset of Figure S1).

To get insights into the electronic transitions of the investigated compound, single crystals of 1-(S,S) and 1-(R,R) were used to record temperature-dependent (4.0-290 K) absorption spectra in the 900-1000 nm range, with unpolarized light propagating perpendicular to the (011) crystallographic plane (Figure 2). The choice of the probed direction was dictated by the shape of the crystals.⁸ The spectra for 1-(R,R) are presented in Figure 2 and those of 1-(S,S) in Figure S2.

<figure><img src="image_3.png" /><figcaption>**Figure 2.** (a) Thermal variation of the absorption coefficient for a single crystal of 1-(R,R) (kL(0,-1,1) in the 900-1000 nm range. The vertical lines correspond to the calculated energy of the transitions (average of Yb1 and Yb2 contributions). (b) Energy diagram for the ²F₇/₂ ← ²F₅/₂ transition split by the crystal field parameters in three main components and calculated values for the two crystallographically independent Yb¹¹¹ ions in the crystal structure obtained from *ab initio* calculations.</figcaption></figure>

The investigated range shows multiple sharp absorption bands between 900 and 1000 nm. These bands are associated to the ²F₇/₂ ← ²F₅/₂ electronic transition of Yb¹¹¹. The presence of three main components centred at ca. 928.0, 957.0 and 977.5 nm is associated with the crystal field splitting of the ²F₇/₂ and ²F₅/₂ ground and excited multiplet, respectively (Figure 2b).²⁰,²¹ The peak at λ = ca. 977.5 nm is associated to the lowest energy 0-1' absorption, which loses intensity as the temperature decreases, while those at λ = ca. 960 nm and λ = ca. 935 nm, associated to the 0-2' and 0-3' transitions, respectively, gain intensity.

*Ab initio* calculations at the Complete Active Space Self Consistent Field (CASSCF),²² followed by N-Electron Valence Perturbation Theory to second order (NEVPT2) were performed to elucidate the electronic structures of both crystallographic Yb¹¹¹ sites. The calculated energy differences between 1', 2' and 3' excited state Kramers doublets are in a very good agreement with the experimental findings (Figure 2 and Tables S1-S4). Notably, the calculated energy difference between the contributions of the two Yb¹¹¹ sites to the optical spectrum is smaller than the experimental full width at half maximum, rendering the two sites optically indistinguishable (Figure 2).

Magnetic field dependent MChD measurements were performed on 1-(R,R) and 1-(S,S) at T = 4.0 K with alternating magnetic fields *B* applied along *k* from 0.0 to 2.0 T. The results are presented in Figure 3a. The *B* dependence of the MChD spectra for the two enantiomers show mirror-image spectral profiles of opposite sign and similar intensity. At 4.0 K, three main MChD signals are observed for each enantiomer with an
intense sharp signal detected at ca. 977.5 nm, a weaker and fine-structured contribution at ca. 955 nm with, and a weak sharp contribution at ca. 923 nm. These MChD signals are in accordance with the absorbance bands recorded at 4.0 K and attributed to the ²F₇/₂ ← ²F₅/₂ electronic transition split by the crystal field and fine-structured (0-2') by vibronic coupling.²⁰,²¹

The magnetic field dependence of the $\Delta A_{MChD}$ signal at $\lambda$ = 977.5 nm is compared to the magnetic field dependence of the magnetization recorded on a microcrystalline sample of 1-(R,R) in similar experimental conditions (Figure 3b). Attempts to perform magnetic measurements on oriented single-crystals were unsuccessful given the small size of the crystals. The magneto-chiral optical data follows the same magnetic field dependence of the sample magnetization, with an almost linear increase in the 0-2 T range, in agreement with previous studies, without reaching saturation.²⁰,²¹

<figure><img src="image_4.png" /><figcaption>**Figure 3.** (a) Magnetic field dependence of $\Delta A_{MChD}$ for 1-(R,R) at T = 4.0 K. Red dashed line is the MChD spectrum for 1-(S,S) at B = 1.0 T. (b) Magnetic field dependence of $\Delta A_{MChD}$ ($\lambda$ = 977.5 nm) compared to the magnetic field dependence of the magnetization collected in similar experimental conditions on a microcrystalline powder of 1-(R,R).</figcaption></figure>

Temperature dependent MChD measurements were carried out on 1-(R,R) and 1-(S,S) in the T = 4.0-290 K range with an alternating magnetic field **B** = 1.0 T applied along **k**. The results are presented in Figure 4a. At low temperature, the signals exhibit absorptive line shapes. This means that the underlying mechanism at the origin of the MChD signal is the variation of the Boltzmann population of the ²F₇/₂ ground state, which contributes to the MChD C term (Barron-Vrbancich theory).²³ At 4.0 K, $k_B T$ is worth 2.78 cm⁻¹, therefore only the lowest energy 0 sublevel is populated. The temperature dependence of the C term with 1/T explains the weakening of the intensity as the temperature increases.¹⁴ Indeed, at ca. 100 K, the signals assume a dispersive line shape and the intensity remains almost constant up to room temperature. This indicates that the temperature independent MChD A term associated to the zero-field splitting of both ground and excited states starts to dominate over the C term.²³ This is in agreement with previous studies.¹⁶,¹⁸⁻²¹,²⁴

The thermal variation of the MChD signal (integrated absolute area of the overall ²F₇/₂ ← ²F₅/₂ multiplet) was compared to the thermal variation of the sample magnetization

at **B** = 1.0 T (Figure S3). The data are in good agreement with those obtained through magnetometry but a deviation is observed in the 24-100 K range. This deviation can be due to the different experimental conditions used for the two measurements.²⁴ While magneto-chiral optical data were collected on oriented single crystals along a specific crystallographic direction, magnetic measurements were performed on a microcrystalline sample of randomly oriented crystallites due to the small size of the single-crystals (vide supra).

Figure 4b shows in detail the MChD spectra obtained at 290 K. A clear derivative type signal is observed at room temperature for both enantiomers. To better quantify the magnitude of the MChD, the MChD dissymmetry factors $g_{MChD}$ (equation S1), which represent the amount of absorption affected by the magnetic field with respect to the natural absorption at zero field, has been extracted at 4.0 and 290 K.

<figure><img src="image_5.png" /><figcaption>**Figure 4.** (a) Temperature dependence of $\Delta A_{MChD}$ for 1-(R,R) at T = 4.0 K. Red and black dashed lines are the MChD spectra for 1-(S,S) at T = 4.0 and 290 K, respectively. (b) Room temperature MChD spectra for 1-(R,R) and 1-(S,S).</figcaption></figure>

The analysis is limited to 1-(R,R), which exhibited the spectra with the highest signal-to-noise ratio, and to the signal at $\lambda$ = 977.5 nm, that has provided a MChD signal above the detection limits of our setup at room temperature. At T = 4.0 K and **B** = 1.0 T, $\Delta A_{MChD}$ is ca. 0.065 cm⁻¹T⁻¹ and the absorption coefficient A is ca. 7 cm⁻¹. This provides a $g_{MChD}$ of 9(1) × 10⁻³ T⁻¹. At T = 290 K and **B** = 1.0 T, $\Delta A_{MChD}$ is ca. 0.007 cm⁻¹T⁻¹ and A = 17 cm⁻¹, which provides a $g_{MChD}$ of 4(1) × 10⁻⁴ T⁻¹. Although the $\Delta A_{MChD}$ can be measured at room temperature, the $g_{MChD}$ values are two orders of magnitude lower than previously investigated Yb¹¹¹ complexes with helicene based ligands at low and room temperature.²⁰,²¹

It is important to analyse the potential reasons of such a reduction of the $g_{MChD}$ factor. First of all, it should be recalled that two crystallographically independent molecules are present in the asymmetric unit. Given the slightly different crystallographic parameters and magnetic response, they are expected to behave similarly. Therefore, the presence of two
independent Yb¹¹¹ sites should weakly contribute to the reduction of the gMChD factors.

The orientation of the magnetic anisotropy axis with respect to the probed direction (Figure S4) may play a more important role. *Ab initio* calculations reveal that the magnetic easy-axis related to the ground Kramers doublet (0) is primarily aligned along the two oxygen from the methoxy groups of the ligand. The orientation of the anisotropic easy-axis within the ligand plane implies that the magneto-optical measurements were performed with an applied magnetic field **B** and light wavevector **k** perpendicular to the anisotropic axis of both crystallographically independent molecules, that are disposed in pairs at ca. 90° with respect to each other (Figure 1).¹⁶

The last consideration concerns the distance of the carbon stereocenters of the chiral ligand with respect to the Yb¹¹¹ ion and their interaction with its *f* orbitals. Given the distance between them and the presence of another metal ion in between (Zn¹¹¹), it is reasonable that the magneto-chiral optical response of the Yb¹¹¹ is reduced. A similar behaviour has been already observed in two chiral heterometallic extended networks where only the electronic transitions of the metal closer to the chiral ligand showed clearly detectable MChD signals.²⁵,²⁶

In the present case, the nature of the Yb¹¹¹ electronic transition, favourable to MChD, can be considered responsible for a signal detectable up to room temperature but the relative intensity of the signal with respect to the overall absorption seems reduced by the magneto-structural considerations described above.

## Conclusions

In conclusion, we have investigated the MChD properties of a Zn¹¹¹/Yb¹¹¹-based chiral molecular nanomagnet exhibiting room temperature magneto-electric coupling.

The magnetic and optical properties are in good agreement with *ab initio* theoretical calculations. MChD measurements reveal a MChD signal associated to the magnetic-dipole allowed ²F₇/₂ ↔ ²F₅/₂ electronic transition, which is retained up to room temperature. Although the MChD signal is clearly detectable at room temperature, the dissymmetry factors gMChD are two orders of magnitude lower than record values reported in the literature.

An analysis of the magneto-structural correlations identifies two key factors for such a reduction: *i*) the magnetic field **B** applied perpendicular to the main anisotropic axis of the ground state and *ii*) the long distance between the source of chirality (sterocenters) and the magnetic center. These findings support previous studies on the magneto-structural and spectroscopic ingredients that are necessary to observe strong MChD responses.

Nevertheless, the obtained results represent the first evidence of the coexistence between magneto-chiral dichroism and magneto-electric coupling at room temperature in a molecular nanomagnet, paving the way for further studies where magneto-chiral anisotropy and magneto-electric coupling interact. Future studies will be focused on *i*) measuring

MChD along the direction of the uncompensated dipolar moment on materials that satisfy the chemical design principles mentioned above to maximize the MChD response while maintaining a net polarization and *ii*) applying an electric field along the probed direction to detect a potential increase of the MChD signal intensity due to the magneto-electric coupling.

## Conflicts of interest

There are no conflicts to declare.

## Data availability

The data supporting this article have been included as part of the Supplementary Information.

## Acknowledgements

The French National Research Agency (ANR) is acknowledged for financial support through Switch-MChD (ANR-23-CE07-0003), PRINCIPE (ANR-23-CE07-0015) and MEMORI (ANR-19-CE07-0026) projects. This project has received financial support from the CNRS through the MITI interdisciplinary programs through its exploratory research program. The authors thank the University of Montpellier, CNRS and PAC of ICGM. J. Long also acknowledges the support from the Institut Universitaire de France.

## Notes and references

1. J. J. Zakrzewski, M. Liberka, J. Wang, S. Chorazy and S. Ohkoshi, *Chem. Rev.*, **2024**, *124*, 5930–6050.

2. A. Stupakiewicz, C. S. Davies, K. Szerenos, D. Afanasiev, K. S. Rabinovich, A. V. Boris, A. Caviglia, A. V. Kimel and A. Kirilyuk, *Nat. Phys.*, **2021**, *17*, 489–492.

3. D. Afanasiev, J. R. Hortensius, B. A. Ivanov, A. Sasani, E. Bousquet, Y. M. Blanter, R. V. Mikhaylovskiy, A. V. Kimel and A. D. Caviglia, *Nat. Mater.*, **2021**, *20*, 607–611.

4. T. Manouras and M. Vamvakaki, *Polym. Chem.*, **2017**, *8*, 74–96.

5. R. Serber, *Phys. Rev.*, **1932**, *41*, 489–506.

6. M. Faraday, *Philos. Trans. R Soc. Lond.*, **1846**, *136*, 1–20.

7. M. Fittipaldi, A. Cini, G. Annino, A. Vindigni, A. Caneschi and R. Sessoli, *Nat. Mater.* **2019**, *18*, 329–334.

8. J. Long, M. S. Ivanov, V. A. Khomchenko, E. Mamontova, J.-M. Thibaud, J. Rouquette, M. Beaudhuin, D. Granier, R. A. S. Ferreira, L. D. Carlos, B. Donnadieu, M. S. C. Henriques, J. A. Paixão, Y. Guari and J. Larionova, *Science*, **2020**, *367*, 671–676.

9. A. K. Boudalis, J. Robert and P. Turek, *Chem. Eur. J.*, **2018**, *24*, 14896–14900.

10. L. D. Barron, *Chem. Soc. Rev.*, **1986**, *15*, 189.

11. G. L. J. A. Rikken and E. Raupach, *Nature*, **1997**, *390*, 493–494.

12. M. Atzori, G. L. J. A. Rikken and C. Train, *Chem. Eur. J.*, **2020**, *26*, 9784–9791.

13. M. Atzori, C. Train, E. A. Hillard, N. Avarvari and G. L. J. A. Rikken, *Chirality*, **2021**, *33*, 844–857.

14. M. Atzori, H. Ludowieg, M. Cortijo, I. Breslavetz, K. Paillot, P. Rosa, C. Train, J. Autschbach, E. A. Hillard and G. L. J. A. Rikken, *Sci. Adv.*, **2021**, *7*, eabg2859.

15. L. D. Barron, *Molecular Light Scattering and Optical Activity*, Cambridge University Press, **2004**.
16 M. S. Raju, K. Paillot, I. Breslavetz, G. Novitchi, G. L. J. A. Rikken, C. Train and M. Atzori, *J. Am. Chem. Soc.*, **2024**, *146*, 23616–23624.

17 F. Pointillart, M. Atzori and C. Train, *Inorg. Chem. Front.*, **2024**, *11*, 1313–1321.

18 C.-Y. Li, L. C. Adi, K. Paillot, I. Breslavetz, L.-S. Long, L.-S. Zheng, G. L. J. A. Rikken, C. Train, X.-J. Kong and M. Atzori, *J. Am. Chem. Soc.*, **2024**, *146*, 16389–16393.

19 L. C. Adi, O. G. Willis, A. Gabbani, G. L. J. A. Rikken, L. Di Bari, C. Train, F. Pineider, F. Zinna and M. Atzori, *Ang. Chem. Int. Ed.*, **2024**, DOI:10.1002/anie.202412521.

20 K. Dhbaibi, M. Grasser, H. Douib, V. Dorcet, O. Cador, N. Vanthuyne, F. Riobé, O. Maury, S. Guy, A. Bensalah-Ledoux, B. Baguenard, G. L. J. A. Rikken, C. Train, B. Le Guennic, M. Atzori, F. Pointillart and J. Crassous, *Ang. Chem. Int. Ed.*, **2023**, DOI:10.1002/ange.202215558.

21 M. Atzori, K. Dhbaibi, H. Douib, M. Grasser, V. Dorcet, I. Breslavetz, K. Paillot, O. Cador, G. L. J. A. Rikken, B. Le Guennic, J. Crassous, F. Pointillart and C. Train, *J. Am. Chem. Soc.*, **2021**, *143*, 2671–2675.

22 F. Neese, The ORCA program system, *WIREs Computational Molecular Science*, **2012**, *2*, 73–78.

23 L. D. Barron and J. Vrbancich, *Mol. Phys.*, **1984**, *51*, 715–730.

24 M. S. Raju, K. Dhbaibi, M. Grasser, V. Dorcet, I. Breslavetz, K. Paillot, N. Vanthuyne, O. Cador, G. L. J. A. Rikken, B. Le Guennic, J. Crassous, F. Pointillart, C. Train and M. Atzori, *Inorg. Chem.*, **2023**, *62*, 17583–17587.

25 M. Atzori, I. Breslavetz, K. Paillot, K. Inoue, G. L. J. A. Rikken and C. Train, *J. Am. Chem. Soc.*, **2019**, *141*, 20022–20025.

26 M. Atzori, I. Breslavetz, K. Paillot, G. L. J. A. Rikken and C. Train, *J. Mater. Chem. C*, **2022**, *10*, 13939–13945.