Low-temperature giant coercivity in metallic Co6.2Ga3.8-xGex(x=2.4 to 3.2) with chemically tunable spin frustration

Abstract

The observation of giant coercivity exceeding 20 kOe at low temperatures in several transition-metal-based compounds has attracted significant attention from a fundamental perspective. This research is also relevant to developing rare-earth-free permanent magnets, wherein cobalt is one of the primary elements used. To facilitate easy fabrication, rare-earth-free and Co-based inorganic bulk magnets that exhibit giant coercivity are highly demanded but rarely reported. Herein, we report the observation of low-temperature giant coercivity in polycrystalline metallic Co6.2Ga3.8-xGex (x=2.4 to 3.2) with the hexagonal Fe13Ge8-type structure composed of Kagome and triangular lattices. As the Ge content x decreases from 3.2, the magnetic ground state changes from ferrimagnetism to ferromagnetism at x=2.6. In the ferrimagnetic state, we observed a signature of spin frustration arising from the Kagome and/or triangular lattices of Co atoms. The ferromagnetic ordering temperatures for the x=2.6 and 2.4 samples are 46 K and 60 K, respectively. The coercive fields rapidly increase upon cooling and reach values of 26 kOe and 44 kOe in the x=2.6 and 2.4 samples, respectively, at 2 K. We discuss the possible origin of the observed giant coercivity in the present system.