Epitaxial Stabilization of Molybdate Pyrochlore Thin Film Near Phase Boundary

In quantum materials, colossal responses can emerge near phase boundaries. The molybdate pyrochlore oxides, <i>R</i>₂Mo₂O₇ (<i>R</i> = rare earth), form a series of compounds where there is a transition from a ferromagnetic metal to a spin glass insulator as a function of the <i>R</i>³⁺ radius [1]. To date, most of the work on this family of materials has been on bulk polycrystalline samples [2]. In this work, we synthesized pyrochlore Gd₂Mo₂O₇ and Tb₂Mo₂O₇ in thin film form using molecular beam epitaxy (MBE); in the bulk samples, Gd₂Mo₂O₇ and Tb₂Mo₂O₇ are a metallic ferromagnet and an insulating spin glass, respectively, both sitting adjacent to the phase boundary. Gd₂Mo₂O₇ thin films show insulating ferromagnetic behavior which is not present in the reported phase diagram of molybdate pyrochlore investigated in bulk form. Our work realizes novel phases of molybdate pyrochlore near phase boundary enabled by the thin film geometry.<br/><br/><b>References</b><br/>[1] J. S. Gardner, M. J. P. Gingras, J. E. Greedan, <i>Rev. Mod. Phys.</i> <b>82</b> (2010) 53<br/>[2] T. Katsufuji, H. Y. Hwang, S.-W. Cheong, <i>Phys. Rev. Lett.</i> <b>84</b> (2000) 1998<br/><br/>This work was supported by the Air Force Office of Scientific Research (MURI Grant No. FA9550-21-1-0429).