Zernike Colloquium - Martha Greenblatt : Designing Polar and Magnetic Oxides in the A2BB'O6-Type Corundum Derivatives

Martha Greenblatt

Department of Chemistry andChemical Biology

Rutgers University

Piscataway, NJ, USA

Polar and magnetic oxides are fundamentally and technically important, but difficult to prepare. Recently, we were able to synthesize, at high pressure and temperature (HPT) in a Walker-type multi-anvil cell, a number of new compounds, A₂BB’O₆ in the corundum-derived and perovskite structure with unusually small A-site cations .^1-5 At HPT the crystal structures of these A₂BB ' O₆ phases allow the incorporation of strong magnetic transition metal ions on all cation sites for magnetic and potentially multiferroic, or magnetoelectric behavior and applications in spintronics. Our aim was to design room-temperature polar ferri- or ferro - magnets by composition modulation of A₂BB ' O₆ phases. So far, we have successfully prepared a series of polar and magnetic oxides and systematically investigated the relationship between the crystal, magnetic, and electronic structure and physical properties. The discovery of polar antiferromagnetic LiNbO₃-type (R3c) Mn₂FeMO₆ (M = Nb, Ta)¹ predicted new polar structures with second-order Jahn-Teller effect ions (such as Nb⁵⁺ and Ta⁵⁺, d⁰) at the B'-site and small ions at the A-site of A₂BB'O₆, which has been confirmed by the preparation of Zn₂FeTaO₆.² In the Ni₃TeO₆-type (R3) ferrimagnetic semiconductor Mn₂FeMoO₆ (T_C ~ 340 K),³ the polarization of the structure, is found to be stabilized by the spin structure at high pressure, while at ambient pressure, a new spin structure with lower energy state induces an unusually low-temperature (~400 - 550 K) cationic rearrangement, which provides a new way to tune the physical properties at the atomic-scale, under relatively mild conditions, of bulk oxides. In polar ferrimagnetic Mn₂FeWO₆ with Ni₃TeO₆-type structure the charge and size difference between Fe²⁺ and W⁶⁺ leads to a fully ordered Fe/W lattice and several exotic magnetic phases⁴. Other A₂BB’O₆ compounds with perovskite or distorted perovskite structures and interesting magnetic properties were also synthesized at HPT, such as Mn₂FeReO₆ which is half-metallic with large magnetoresistance and orders ferri-magneticaly at 520 K.⁵ While all of these materials are multiferroic, none studied thus far exhibits ferroelectric switching; the search continues .

References

1. Li, M.-R.; Walker, D.; Retuerto, M.; Sarkar, T.; Hadermann, J.; Stephens, P. W.; Croft, M.; Ignatov, A.; Grams, C. P.; Hemberger, J.; Nowik, I.; Halasyamani, P. S.; Tran, T. T.; Mukherjee, S.; Dasgupta, T. S.; Greenblatt, M. Angew. Chem. Int. Ed. 2013, 52, 8406.

2. Li, M.-R.; Stephens, P. W.; Retuerto, M.; Sarkar, T.; Grams, C. P.; Hemberger, J.; Croft, M. C.; Walker, D.; Greenblatt, M. J. Am. Chem. Soc. 2014, 136, 8508.

3. Li, M.-R.; Retuerto, M.; Walker, D.; Sarkar, T.; Stephens, P. W.; Mukherjee, S.; Dasgupta, T. S.; Hodges, J. P.; Croft, M.; Grams, C. P.; Hemberger, J.; Sánchez-Benítez, J.; Huq, A.; Saouma, F. O.; Jang, J. I.; Greenblatt, M. Angew. Chem. Int. Ed. 2014, 53, 10774.

4. Li, M.-R.; Croft, M.; Stephens, Peter, W.; Ye, M.; Vanderbilt, D.; Retuerto, M.; Deng, Z.; Grams, Christoph P. ; Hemberger, J .; Hadermann, J.; Li, W . -M .; Jin, C-Q.; Saouma, F. O.; Jang, J . I . ; Akamatsu, H ., Gopalan, V; Walker, D; Greenblatt , M. Adv. Mater. 2015, 27, 2177.

5. Man-Rong Li, Maria Retuerto, Zheng Deng, Peter W. Stephens, Mark C. Croft, Qingzhen Huang, Hui Wu, Xiaoyu Deng, Gabriel Kotliar, Javier Sánchez-Benítez, Joke Hadermann, David Walker, Martha Greenblatt, Angew. Chem. Int. Ed., 2015 , 54, 1.