Transition metal thiophosphates have been well studied with respect to both their magnetic and structural properties, whereas alkali transition metal thiophosphates are not as well studied. The primary focus of this research are Li2FeP2S6 and Li2CoP2S6. Phase pure powders and single crystals of both Li2FeP2S6 and Li2CoP2S6 were synthesized via a solid-state method. The crystal structure of Li2FeP2S6 was determined to have a layered honeycomb P-31m lattice. This structure had been previously reported, but prior to this research, no magnetic properties of this material had been studied. Susceptibility and field dependent magnetometry measurements of Li2FeP2S6 demonstrate a transition from an ordered antiferromagnetic state to a disordered paramagnetic state at 25 K. The cobalt counterpart is even less well-known, neither the nuclear nor the magnetic properties have been reported. The novel crystal structure of LixCoyP2S6 was solved using single crystal x-ray diffraction data. Structurally, the iron and the cobalt thiophosphates are similar but not identical. The largest discrepancy in nuclear structure is the partial disorder in the thiophosphates, the P-P bond forms across the lithium layer instead of the cobalt layer approximately 5% of the time. To our surprise, even though the nuclear structure remains largely unaffected, changing the transition metal from iron to cobalt affects the magnetic properties significantly. The susceptibility data for the cobalt sample shows complete paramagnetic behavior down to 5 K. In addition to this, there was no hysteresis in the field dependent measurements, confirming paramagnetic ordering. This study is only scratching the surface of fully understanding both the physical and magnetic properties of these materials. The potential applications are endless: magnetoelectrics, ferrotoroidics, quantum spin liquids, and much more.

Magnetic and structural properties of lithium transition metal thiophosphates Li2CoP2S6 and Li2FeP2S6

ACS Spring Meeting 2021

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