Pressure-Driven Transitions in La2CoTiO6: Antiferromagnetic Insulator to Nonmagnetic Metal via Antiferromagnetic Metal in a Double Perovskite Oxide

Abstract

In double perovskite oxides (A${}_2$BB${}^{\prime }$O${}_6$), magnetism often arises from diluted magnetic lattices, created by combining a perovskite structure with localized 3$d$ magnetic elements (B) alongside another perovskite lattice containing nearly nonmagnetic delocalized 4$d$/$5d$ elements (B${}^{\prime }$). Alternatively, the magnetic lattice can consist entirely of 3$d$ elements, with one being completely nonmagnetic with $d^0$ state. La${}_2$CoTiO${}_6$ (LCTO), a representative double perovskite oxide, contains Ti in a nonmagnetic state with a $d^0$ electron configuration due to its $4^{+}$ oxidation state. Experimental evidence shows that LCTO possesses a monoclinic structure (space group $P{2}_1/n$) and behaves as an antiferromagnet with a Néel temperature of 14.6 K. Through first-principle electronic structure calculations, we uncover that adjusting external hydrostatic pressure induces a sequence of phase transitions: from antiferromagnetic insulator (AFM-I) to antiferromagnetic metal (AFM-M), and ultimately to itinerant nonmagnetic metal (NM-M). The transition from AFM-I to AFM-M at $\sim$ 42 GPa pressure coincides with a shift in spin states, moving from a high-spin (HS) state to a low-spin (LS) state, while Co retains a $d^7$ configuration. Distortion within the monoclinic structure under pressure plays a pivotal role in the spin-state transition. At the AFM-I to AFM-M transition, we observe a sharp decrease in the ratio of the octahedral volumes occupied by Co and Ti. Such change in ratio is linked to variations in octahedral volumes, akin to a breathing mode distortion. We explore the impact of the breathing mode distortion by examining a highly symmetric theoretical structure (space-group $I4/mmm$), achieved by optimizing the structure with all $\angle${Co-O-Ti} angles set to 180${}^{\circ }$.

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Cited by in corpus (1)

• Tuning Magnetic and Electronic Properties of Double Perovskite La${}_2$CoIr${}_{1-x}$Ti${}_x$O${}_6$