# 1:1 Ca2+:Cu2+ A-site order in a ferrimagnetic double double perovskite

Elena Solana Madruga, Padraig S. Kearins, Clemens Ritter, Angel Arevalo

Lopez, J. Paul Attfield

► To cite this version:

Elena Solana Madruga, Padraig S. Kearins, Clemens Ritter, Angel Arevalo Lopez, J. Paul Attfield. 1:1 Ca2+:Cu2+ A-site order in a ferrimagnetic double double perovskite. Angewandte Chemie International Edition, 2022, 61 (40), pp.e202209497. 10.1002/anie.202209497. hal-04142726

HAL Id: hal-04142726

https://hal.univ-lille.fr/hal-04142726

Submitted on 27 Jun 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Perovskites

# 1:1 Ca²⁺:Cu²⁺ A-site Order in a Ferrimagnetic Double Double Perovskite

Elena Solana-Madruga,* Padraig S. Kearins, Clemens Ritter, Ángel M. Arévalo-López, and J. Paul Attfield*

How to cite: Angew. Chem. Int. Ed. 2022, 61, e202209497

International Edition: doi.org/10.1002/anie.202209497

German Edition: doi.org/10.1002/ange.202209497

**Abstract:** Cation ordering in ABX₃ perovskites is important to structural, physical and chemical properties. Here we report discovery of CaCuFeReO₆ with the tetragonal AA'BB'O₆ double double perovskite structure that was previously only reported for A'=Mn compositions. CaCuFeReO₆ occurs in the same phase field as CaCu₃Fe₂Re₂O₁₂ demonstrating that different A-cation ordered peroskites may be obtained in the same chemical system. CaCuFeReO₆ has ferrimagnetic order of Fe, Re and Cu spins below T_c=567 K, in contrast to Mn analogues where the Mn spins order separately at much lower temperatures. The magnetoresistance of CaCuFeReO₆ displays low-field "butterfly" hysteresis with an unusual change from negative to positive values as field increases. Many more AA'BB'O₆ double double perovskites may be accessible for A'=Cu and other divalent transition metals at high pressure, so the presently known phases likely represent only the "tip of the iceberg" for this family.

ABO₃ perovskite oxides are important for a wide range of chemical and physical properties.[1,2] Cation ordering within the perovskite lattice can generate emergent physical properties,[3] notably in A₂BB'O₆ double perovskites (DPv) where rock-salt ordering of B/B' transition metal cations[4-6]

leads to ferrimagnetism and large magnetoresistance in Sr₂FeMoO₆ and related materials.[7-9] More complex perovskites featuring order of alkali metal, alkaline earth or rare earth A cations with A' transition metal ions in addition to the latter B/B' order enable effects of the magnetic A' transition metal ions on the B/B' ferrimagnetism to be explored. Two such classes of compounds have been reported, both requiring high pressure synthesis to stabilise cation order based on size difference between the large A and small transition metal A' cations as substantial tilts of the B/B'O₆ octahedra reduce the A' coordination number from 12 in the ideal perovskite structure to 4 in the ordered derivatives. AA'₃B₂B'₂O₁₂ (referred to as 1322-type) materials have a cubic (space group Pn-3) structure with 1:3 order of 12-coordinate A and 4-coordinate square-planar A' cations, and are formed predominantly for A'=Cu. Ferromagnets with Curie temperatures (T_c) > 300 K are found for CaCu₃B₂B'₂O₁₂ (B/B'=Fe/Re, Fe/Os, Mn/Os)[9-11] and ACu₃Fe₂Os₂O₁₂ (A=Na, La)[12,13] materials, with lower temperature ferri- or antiferro- magnetic orders in other analogues; CaCu₃B₂B'₂O₁₂ (B/B'=Ga/Sb, Cr/Sb, Fe/Sb, Fe/Nb),[14-17] LaCu₃Co₂Re₂O₁₂[18] and LaMn₃Ni₂Mn₂O₁₂.[19] The latter is the only A'=Mn (and non-Cu) 1322 phase reported to date.

The second group of A/A' and B/B' ordered perovskites have AA'BB'O₆ stoichiometry and are labelled double double (or doubly ordered) perovskites (DDPv's) following the "double perovskite" description for AA'B₂O₆ or A₂BB'O₆ materials with cation order at only one type of site.[3] They have tetragonal P4₂/n symmetry with columnar ordering of 10-coordinate A and 4-coordinate A' cations, and all previously reported materials are based on A'=Mn. RMnMnB'O₆ (R=rare earth) series are reported for B'=Sb[20,21] and Ta,[22] and many CaMnBB'O₆ materials (B=Mn, Fe, Co, Ni for B'=Re,[23,24,25] and B/B'=Fe/Ta,[26] Cr/Sb and Fe/Sb[27]) were also synthesised at high temperatures and pressures. High temperature ferrimagnetism was reported in CaMnFeReO₆ (T_c=500 K) and also a Cu-doped derivative of nominal composition Ca(Mn₀.₅Cu₀.₅)FeReO₆ (T_c=560 K), with an unusual switch between negative and positive magnetoresistances in the latter at low temperatures.[23] The latter material suggests that DDPv's stabilised by A/Cu ordering, without any Mn content, may be accessible. This offers the exciting possibility of being able to stabilise AA'₃B₂B'₂O₁₂ (1322) and AA'BB'O₆ (DDPv) cation ordered perovskites in the same A–A' (=Cu)-B–B' chemical system for the first time, and hence compare effects of the 1:3 and 1:1 A:Cu orders on the magnetic and electronic properties

[*] Dr. E. Solana-Madruga, P. S. Kearins, Prof. J. P. Attfield
Centre for Science at Extreme Conditions (CSEC) and School of Chemistry, University of Edinburgh
Mayfield Road, Edinburgh EH9 3JZ (UK)
E-mail: j.p.attfield@ed.ac.uk

Dr. E. Solana-Madruga
Departamento de Química Inorgánica, Facultad CC. Químicas,
Universidad Complutense de Madrid (Spain)
E-mail: elsolana@ucm.es

Dr. C. Ritter
Institut Laue-Langevin
38042 Grenoble Cedex (France)

Dr. Á. M. Arévalo-López
Univ. Lille, CNRS, Centrale Lille, Univ. Artois, UMR 8181, UCCS,
Unitéde Catalyse et Chimie du Solide
59000 Lille (France)

<figure><img src="image_2.png" /></figure>

© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
of the B/B' sublattice. Here we report synthesis of a Mn-free, high-$T_C$ DDPv material CaCuFeReO$_6$ and comparison of properties to the previously reported CaCu$_3$Fe$_2$Re$_2$O$_{12}$.[9]

Samples of nominal composition CaCuFeReO$_6$ were heated under pressures of 10–15.5 GPa using stoichiometric mixtures of Ca$_2$Fe$_2$O$_5$, ReO$_2$ and CuO in a Walker-type module as described in Supporting Information. A component with the $P4_2/n$ DDPv type structure was identified by powder X-ray diffraction within multiphase products. Optimum samples were synthesised at 15.5 GPa and 1400 °C and were characterised by powder synchrotron X-ray diffraction at 300 K, neutron diffraction patterns from 5 to 550 K, and magnetic and electronic transport measurements (details in Supporting Information).

The crystal structure of CaCuFeReO$_6$ was refined using synchrotron X-ray[28] and neutron powder diffraction profiles. 6.8(2)% Fe/Re antisite disorder was found from the X-ray fit (full results are in Supporting Information) and this value was fixed in all neutron refinements. The $A'=\text{Cu}$ cation columns have two inequivalent sites with tetrahedral (Cu1) and square planar (Cu2) coordinations. Refinement against powder neutron data (Figure 1) showed that 29(1) and 0(1)% of Fe was substituted at the Cu1 and Cu2 sites, respectively, so their occupancies were fixed as 70%Cu/30%Fe and 100%Cu in subsequent variable temperature neutron fits.

Magnetic diffraction peaks from CaCuFeReO$_6$ (Figure 1) were observed in all neutron diffraction patterns from 5 to 550 K. Peaks from ordered moments at both A-site Cu

and B/B' Fe/Re are observed. The magnetic peaks are indexed by propagation vector [0 0 0] and good fits were obtained from a ferrimagnetic model with spins parallel to the c-axis (Figure 2). The small Re spin was found to be unstable in initial magnetic refinements and was constrained to be antiparallel to the Fe moment as done in previous refinements of Mn-based CaA'FeReO$_6$ materials.[23] The two Cu site spins were both found to be parallel to the Fe spin and were constrained to be equal in the final refinements. Results of the refinement of crystal and magnetic structures against powder neutron diffraction data are shown in Figures 1 and 2 and are tabulated in Supporting Information.

The crystal structure refinements demonstrate that the present CaCuFeReO$_6$ sample is slightly off-stoichiometric with refined composition CaCu$_{0.85}$Fe$_{1.15}$ReO$_6$ and also with 7% Fe/Re antisite disorder. Fe shows a clear preference for substituting at the tetrahedral (Cu1) rather than the square planar (Cu2) site. Nevertheless the material shows a very high degree of order of four different metals over five cation sites, and demonstrates that the double double perovskite arrangement, previously reported only for Mn-based materi-

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Rietveld fits of the DDPv structure of CaCuFeReO$_6$ against NPD data at 320 K showing the full range of data (top) and at 5 K showing the low-angle magnetic peaks (bottom), labelled $m_A/m_B/m$ to show peaks from spins at A/B/(A and B) type cation sites. Markers from top to bottom show CaCuFeReO$_6$ DDPv (82(1) w.t.%), CaCuFeReO$_6$ DPPv (5.3(3) %), ReO$_2$ (7.4(4) %) and Re (4.8(3) %).</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 2.** a) Refined crystal and magnetic structures for CaCuFeReO$_6$ with Fe, Re and Cu magnetic moments as red, grey and blue arrows, respectively. b) Refined magnetic moments vs. temperature with critical functions fitted in the $T_c/2 < T < T_c$ temperature range.</figcaption></figure>
als, can be stabilised at pressure by Ca/Cu ordering over A/
A' columns.

Bond valence sum calculations using the 320 K neutron
bond lengths give BVS values Ca=2.3, Cu1=1.6, Cu 2=1.5,
Fe=2.6 and Re=5.1. These are consistent with the ideal
valence distribution Ca²⁺Cu²⁺Fe³⁺Re⁵⁺O₆ which is analo-
gous to those in related materials such as Ca²⁺Mn²⁺Fe³⁺
Re⁵⁺O₆,[²³] allowing for disorder at some sites and structural
strain induced by high pressure synthesis. Octahedral tilt
angles calculated from Fe–O–Re angles along the c axis (φ=
19.3(4)°) and within the ab plane (θ=17.4(2)°) are within
the range of 15 to 19.5° for Mn-based analogues[²⁰] and thus
demonstrate that these substantial tilts are essential to
stabilisation of this DDPv structure type.

The same ferrimagnetically ordered spin structure (Fig-
ure 2a) was observed in CaCuFeReO₆ from 5 to 550 K, and
thermal variations of the refined magnetic moments are
shown in Figure 2b. The two independently refined magnetic
moments (Fe/Re and Cu1/Cu2) both follow the same critical
dependence ≈[1-(T/T<sub>C</sub>)]<sup>β</sup> with fitted T<sub>C</sub>=566.70(3) K and
β=0.254(2). The latter is close to the ideal mean field value
of β=0.25 for a tricritical transition, on the cusp between
first and second order behaviour. This may reflect the
complex network of interactions between four distinct spin
sublattices. Ordered moments at 5 K of 3.0 and 1.2 µ<sub>B</sub> for
Fe<sup>3+</sup> and Re<sup>5+</sup> (refined in a 5:2 ratio) are reduced from
ideal values of 5 and 2 µ<sub>B</sub> reflecting B/B' antisite disorder
and spin-orbit coupling for Re<sup>5+</sup>. However the average
moment at 5 K for the Cu sites of 1.4 µ<sub>B</sub> exceeds the ideal
1 µ<sub>B</sub> value for Cu<sup>2+</sup> showing that the Fe spins substituted at
the Cu sites are also aligned. Mössbauer spectroscopy would
be useful for further characterisation of the Fe states at the
Cu sites.

Physical properties of CaCuFeReO₆ were explored
through magnetisation and resistivity measurements in zero
and applied fields. Magnetic susceptibility, shown in Fig-
ure 3a, reveals a single Curie transition. The estimated T_C =
551 K, from extrapolation of the steepest negative χ-T slope
to χ=0, is in agreement with the value of T_C = 567 K from
fitting the zero field neutron moments above. A Curie-
Weiss fit to data at 600-625 K gives realistic results despite
the narrow fitting range; an effective paramagnetic moment
of μ<sub>eff</sub> = 6.52 μ<sub>B</sub>/f.u., close to the spin-only estimate of
6.78 μ<sub>B</sub>/f.u., and a Weiss temperature of θ = 522 K, compara-
ble to T<sub>C</sub> and showing that 3D ferrimagnetic order occurs
with little frustration. Magnetisation-field hysteresis loops
confirm the ferrimagnetic order, with a saturated magnetic
moment of 4 μ<sub>B</sub>/f.u. (Figure 3b) at 2 and 100 K identical to
the value expected for order of S = 1/2 ↑ Cu<sup>2+</sup>, S = 5/2 ↑ Fe<sup>3+</sup>,
and S = 1 ↓ Re<sup>5+</sup> spins, confirming the arrangement derived
from neutron diffraction. The saturated moment decreases
to 2.7 μ<sub>B</sub> at 400 K (see Supporting Information). Small
coercive fields of 120 and 97 mT are observed at 2 and
100 K respectively, reflecting the weak anisotropy of the
tetragonal DDPv structure.

The resistivity of a ceramic pellet of CaCuFeReO₆ is
140 mΩcm at room temperature increasing to 210 mΩcm to
4 K (Figure 2a). This change corresponds to an energy gap
of ≈1 meV which is unrealistically small for intrinsic semi-

conducting behaviour suggesting that grain boundary resis-
tances mask an underlying metallic conductivity. Magneto-
resistance (MR) values in Figure 3b are small, most likely
due to the Fe/Re antisite disorder, but show interesting
variations with field. The negative low field effect is a typical
spin-valve-type magnetoresistance due to the intergrain
tunneling of spin-polarized conduction carriers, as observed
in Sr<sub>2</sub>FeMoO<sub>6</sub> and other ferromagnetic double perovskites.
However a positive MR effect dominates at high fields. A
similar switch from negative to positive MR was reported in
the related Ca(Mn<sub>0.5</sub>Cu<sub>0.5</sub>)FeReO<sub>6</sub> DDPv<sup>[23]</sup> and in the DPv
Mn<sub>2</sub>FeReO<sub>6</sub><sup>[29,30]</sup> due to canting of Fe and Re spins arising
from frustration of their order with respect to the Mn spins
as field increases, and a similar mechanism may operate
here due to their interactions with the Cu site spins. Low
field “butterfly” MR hysteresis curves are observed but the
hysteresis in MR differs slightly from that in the magnet-
ization as the peak-to-peak MR separations do not coincide
with the coercive fields. The behavior is also observed in
Sr<sub>2</sub>FeMoO<sub>6</sub> and the 1322-type analogue to CaCuFeReO<sub>6</sub>,
CaCu<sub>3</sub>Fe<sub>2</sub>Re<sub>2</sub>O<sub>12</sub>,<sup>[9]</sup> and for epitaxial Fe<sub>3</sub>O<sub>4</sub> films and
NiCo<sub>2</sub>O<sub>4</sub><sup>[31,32]</sup>

<figure><img src="image_5.png" /><figcaption>**Figure 3.** a) FC-ZFC (red-black) magnetic susceptibility (left) and inverse (right) of CaCuFeReO₆. Inset shows T-dependence of resistivity.
b) Hysteresis loops and butterfly-shaped magnetoresistance at 2 and 100 K.</figcaption></figure>
CaCuFeReO₆ is an important discovery in the field of cation-ordered perovskites as it demonstrates that the P4₂/n AA'BB'O₆ double double perovskite (DDPv) structure already reported for many RMnBB'O₆ and CaMnBB'O₆ materials can also be stabilised for A' = Cu. CaCuFeReO₆ is the first reported Mn-free DDPv. Synthesis of CaCuFeReO₆ has proved more challenging than for the CaMnFeReO₆ analogue.[23] The present neutron sample of CaCuFeReO₆ was recovered from 15.5 GPa and 1400 °C, has 82% phase purity, with 7% Fe/Re antisite disorder and 30% Fe substituted at one of the Cu sites, whereas CaMnFeReO₆, prepared at 10 GPa and 1400 °C was >99% phase pure with 3% Fe/Re antisite disorder and 8 and 16% Fe at the two Cu sites. Nevertheless this study indicates that increasing pressure significantly above 10 GPa may enable many more AA'BB'O₆ DDPvs to be synthesised for A'=Cu and perhaps other divalent A'=Fe, Co, Ni... cations, so the presently known phases likely represent only the "tip of the iceberg" of DDPv materials.

Interesting differences between the physical properties of CaCuFeReO₆ and CaMnFeReO₆ are apparent. Both have high T_c's for ferrimagnetic Fe/Re spin order, of 567 and 500 K respectively, typical for A₂FeReO₆ double perovskites, but the Cu spins also order at T_c in CaCuFeReO₆ whereas the A-site Mn spins in CaMnFeReO₆ order at a separate transition at T_A=70 K.[9] Order of Mn²⁺ spins at T_A=75 K, well below T_c=520 K, is also seen in the double perovskite Mn₂FeReO₆.[28,29] These differences evidence stronger Fe/Re-O-A' superexchange for A'=Cu compared to A'=Mn, and perhaps also a shift in relative values of the various exchange interactions so that A' spins in CaCuFeReO₆ are less magnetically frustrated. CaMnFeReO₆ has negative MR diverging to large values at low temperature and high field (-32% at 20 K and 7 T), typical for ferrimagnetic double perovskites like Sr₂FeMoO₆,[7] whereas CaCuFeReO₆ shows a switch from negative to positive MR with increasing field. A similar switch in Mn₂FeReO₆ results from increased canting of Fe and Re spins due to frustration of their order with respect to the Mn spins as field increases. High field neutron diffraction experiments would be needed to verify the same effect in CaCuFeReO₆. It is also interesting to compare the mixed DDPv Ca(Mn₀.₅Cu₀.₅)FeReO₆[23] to CaA'FeReO₆ (A'=Cu and Mn). Ca(Mn₀.₅Cu₀.₅)FeReO₆ has T_c=560 K and a separate ordering transition at T_A=150 K unlike in CaCuFeReO₆, but the increase relative to T_A=70 K in CaMnFeReO₆ demonstrates the effect of Cu in strengthening Fe/Re-O-A' superexchange. However Ca(Mn₀.₅Cu₀.₅)FeReO₆ displays a switch from negative to positive MR on warming, as seen in CaCuFeReO₆ (e.g. by comparing 2 and 100 K MR values in a 3 T field in Figure 3b) but not in CaMnFeReO₆. Such complex MR behaviour is therefore not directly linked to the presence (or absence) of a distinct ordering transition of A-site spins, but rather to field effects on competing A'-O-B, A'-O-B' and B-O-B' interactions within AA'BB'O₆ DDPvs with ordered A', B and B' spin sublattices.

Formation of CaCuFeReO₆ is also important because a 1322 type phase CaCu₃Fe₂Re₂O₁₂ (written here as Ca₁/₂Cu₃/₂FeReO₆ for comparison) is also known and so this is the

first demonstration that two different A-cation ordered perovskites can be prepared within the same chemical system. Comparison of their properties is again instructive. CaCuFeReO₆ and Ca₁/₂Cu₃/₂FeReO₆ have similar T_c's of 567 and 560 K with Cu spins ordering parallel to Fe spins at T_c leading to large saturated magnetisations of 4.0 and 4.35 µB respectively, the latter value reflecting the extra 0.5 Cu²⁺ spin per double perovskite unit. Both materials have apparent metallic conductivity but with resistive grain boundaries in ceramic samples. A high spin-polarization of conduction electrons was reported for Ca₁/₂Cu₃/₂FeReO₆ and both materials display low-field "butterfly" spin-valve MR effects although the magnitude of MR is small. However, Ca₁/₂Cu₃/₂FeReO₆ has negative MR while CaCuFeReO₆ shows an unusual switch to positive values at high field. Exploration and comparison of DDPv, 1322 type, and perhaps other types of A and B-site ordered perovskites in mixed transition metal oxide systems is likely to lead to discovery of spintronic and other types of interesting property.

In conclusion, discovery of CaCuFeReO₆ marks an important milestone in development of A- and B- cation ordered perovskites, as it demonstrates that the tetragonal AA'BB'O₆ double double perovskite structure, previously only reported for A'=Mn, can be stabilised by Cu and perhaps other metals at pressures above 10 GPa. CaCuFeReO₆ occurs in the same phase field as 1322-type CaCu₃Fe₂Re₂O₁₂ demonstrating that different A-cation ordering types may be obtained in the same chemical system. Ferrimagnetic Fe (up), Re (down) and Cu (up) spin order occurs in CaCuFeReO₆ below T_c=567 K and magnetoresistance shows low-field spin-valve-type butterfly hysteresis with an unusual change from negative to positive values as field increases.

## Acknowledgements

We thank EPSRC and STFC for support, and Diamond and the ILL for beamtime provided at I11 and D20 beamlines respectively. Stephen Thompson is acknowledged for assistance on I11 data collection. AMAL thanks the ANR-AMANTS project (19-CE08-0002-01). Chevreul Institute (FR 2638), Region Hauts-de-France, and FEDER are acknowledged for funding the PPMS magnetometer.

## Conflict of Interest

The authors declare no conflict of interest.

## Data Availability Statement

The data that support the findings of this study are available in the Supporting Information of this article.
**Keywords:** Double Perovskites · High-Pressure Chemistry · Magnetic Properties · Solid-State Structures

[1] R. J. Tilley, *Perovskites: structure–property relationships*, Wiley, Hoboken, **2016**.

[2] J. P. Attfield, P. Lightfoot, R. E. Morris, *Dalton Trans.* **2015**, *44*, 10541–10542.

[3] G. King, P. M. Woodward, *J. Mater. Chem.* **2010**, *20*, 5785–5796.

[4] M. T. Anderson, K. B. Greenwood, G. A. Taylor, K. R. Poeppelmeier, *Prog. Solid State Chem.* **1993**, *22*, 197–233.

[5] C. J. Howard, B. J. Kennedy, P. M. Woodward, *Acta Crystallogr. Sect. B* **2003**, *59*, 463–471.

[6] S. Vasala, M. Karppinen, *Prog. Solid State Chem.* **2015**, *43*, 1–36.

[7] K.-I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, Y. Tokura, *Nature* **1998**, *395*, 677–680.

[8] D. Serrate, J. De Teresa, M. Ibarra, *J. Phys. Condens. Matter* **2007**, *19*, 023201.

[9] W.-T. Chen, M. Mizumaki, H. Seki, M. S. Senn, T. Saito, D. Kan, J. P. Attfield, Y. Shimakawa, *Nat. Commun.* **2014**, *5*, 3909.

[10] S. Sidi Ahmed, G. D. Ngantso, L. Bahmad, A. Benyoussef, A. E. Kenza, *Phys. Lett. A* **2018**, *382*, 186–192.

[11] L. Gao, X. Wang, X. Ye, W. Wang, Z. Liu, S. Qin, Z. Hu, H.-J. Lin, S.-C. Weng, C.-T. Chen, P. Ohresser, F. Baudelet, R. Yu, C. Jin, Y. Long, *Inorg. Chem.* **2019**, *58*, 15529–15535.

[12] X. Wang, M. Liu, X. Shen, Z. Liu, Z. Hu, K. Chen, P. Ohresser, L. Nataf, F. Baudelet, H.-J. Lin, C.-T. Chen, Y.-L. Soo, Y.-f. Yang, C. Jin, Y. Long, *Inorg. Chem.* **2019**, *58*, 320–326.

[13] X. Ye, X. Wang, Z. Liu, B. Zhou, L. Zhou, H. Deng, Y. Long, *Dalton Trans.* **2022**, *51*, 1745–1753.

[14] S.-H. Byeon, M. W. Lufaso, J. B. Parise, P. M. Woodward, T. Hansen, *Chem. Mater.* **2003**, *15*, 3798–3804.

[15] S.-H. Byeon, S.-S. Lee, J. B. Parise, P. M. Woodward, N. H. Hur, *Chem. Mater.* **2005**, *17*, 3552–3557.

[16] H. Xiang, J. Wang, J. Meng, Z. Wu, *Comput. Mater. Sci.* **2009**, *46*, 307–309.

[17] M. Senn, W.-t. Chen, T. Saito, S. García-Martín, J. P. Attfield, Y. Shimakawa, *Chem. Mater.* **2014**, *26*, 4832–4837.

[18] Z. Liu, X. Wang, X. Ye, X. Shen, Y. Bian, W. Ding, S. Agrestini, S.-C. Liao, H.-J. Lin, C.-T. Chen, S.-C. Weng, K. Chen, P. Ohresser, L. Nataf, F. Baudelet, Z. Sheng, S. Francoual, J. R. L. Mardegan, O. Leupold, Z. Li, X. Xi, W. Wang, L. H. Tjeng, Z. Hu, Y. Long, *Phys. Rev. B* **2021**, *103*, 014414.

[19] Y.-Y. Yin, M. Liu, J.-H. Dai, X. Wang, L. Zhou, H. Cao, C. de la Cruz, C.-T. Chen, Y. Xu, X. Shen, R. Yu, J. A. Alonso, A. Muñoz, Y.-F. Yang, C. Jin, Z. Hu, Y. Long, *Chem. Mater.* **2016**, *28*, 8988–8996.

[20] E. Solana-Madruga, Á. M. Arévalo-López, A. J. Dos Santos-García, E. Urones-Garrote, D. Ávila-Brande, R. Sáez-Puche, J. P. Attfield, *Angew. Chem. Int. Ed.* **2016**, *55*, 9340–9344; *Angew. Chem.* **2016**, *128*, 9486–9490.

[21] E. Solana-Madruga, Á. M. Arévalo-López, A. J. Dos Santos-García, C. Ritter, C. Cascales, R. Sáez-Puche, J. P. Attfield, *Phys. Rev. B* **2018**, *97*, 134408.

[22] K. Ji, Y. Yuan, G. T. Moy, C. Ritter, J. P. Attfield, *J. Solid State Chem.* **2022**, *313*, 123329.

[23] G. M. McNally, Á. M. Arévalo-López, P. Kearins, F. Orlandi, P. Manuel, J. P. Attfield, *Chem. Mater.* **2017**, *29*, 8870–8874.

[24] G. M. McNally, A. M. Arévalo-López, F. Guillou, P. Manuel, J. P. Attfield, *Phys. Rev. Mater.* **2020**, *4*, 064408.

[25] E. Solana-Madruga, Y. Sun, Á. M. Arévalo-López, J. P. Attfield, *Chem. Commun.* **2019**, *55*, 2605–2608.

[26] P. Kearins, E. Solana-Madruga, K. Ji, C. Ritter, J. P. Attfield, *J. Phys. Chem. C* **2021**, *125*, 9550–9555.

[27] E. Solana-Madruga, P. S. Kearins, K. N. Alharbi, C. T. Lennon, C. Ritter, J. P. Attfield, *Phys. Rev. Mater.* **2021**, *5*, 054412.

[28] Deposition Number 2194053 contains the supplementary crystallographic data for this paper. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service.

[29] M.-R. Li, M. Retuerto, Z. Deng, P. W. Stephens, M. Croft, Q. Huang, H. Wu, X. Deng, G. Kotliar, J. Sánchez-Benítez, J. Hadermann, D. Walker, M. Greenblatt, *Angew. Chem. Int. Ed.* **2015**, *54*, 12069–12073; *Angew. Chem.* **2015**, *127*, 12237–12241.

[30] A. M. Arévalo-López, G. M. McNally, J. P. Attfield, *Angew. Chem. Int. Ed.* **2015**, *54*, 12074–12077; *Angew. Chem.* **2015**, *127*, 12242–12245.

[31] P. Li, L. T. Zhang, W. B. Mi, E. Y. Jiang, H. L. Bai, *J. Appl. Phys.* **2009**, *106*, 033908.

[32] P. Li, C. Xia, D. Zheng, P. Wang, C. Jin, H. Bai, *Phys. Status Solidi* RRL **2016**, *10*, 190–196.

Manuscript received: June 29, 2022

Accepted manuscript online: August 8, 2022

Version of record online: August 26, 2022