Researchers find that high magnetic field facilitates new ferromagnetic polar metals

Researchers have designed a new oxide material, Ca₃Co.₃O₈, through atomically precise manipulation of crosslinked oxides. It demonstrated a remarkable combination of properties—ferromagnetism, polar distortion, and metallicity—which shines the spotlight on polar metals and sparks considerable scientific interest.

This achievement was published in Materials of Nature. The collaboration included Prof. Sheng Zhigao from the Hefei Institute of Physical Sciences (HFIPS) of the Chinese Academy of Sciences (CAS), Professor Yu Pu’s team from Tsinghua University and the users of the Stable High Magnetic Field Facility (SHMFF) at HFIPS.

In the traditional sense, electric polarization and magnetic order in materials were seen as mutually exclusive. However, the concept of polar metals was proposed, suggesting that these materials could simultaneously exhibit electrical polarization and metallic properties.

The integration of ferromagnetism in polar metals remains a challenge, as it involves reconciling the inherent contradiction between polarization, ferromagnetism and metallicity within a single material, presenting a significant scientific hurdle.

In this study, the researchers explored the use of oxygen polyhedra to control material properties, leading to the creation of a new nearly two-dimensional functional oxide called Ca.₃Co.₃O₈. This material combines features from the two-layer Ruddlesden-Popper (RP) structure and the brownmillerite (BM) structure.

They used SHMFF’s nonlinear optical testing system to confirm the significant polarization ordering in Ca₃Co.₃O₈. They found that the displacement of Co ions in the CoO6 bilayer octahedron was the main contributor to the polarity.

Using the water-cooled SHMFF magnetic system to test electrical transport, the team also observed a significant topological Hall effect in the material.

These results provide an ideal material platform for exploring correlated electrical and magnetic properties and provide a new perspective for the design of crosslinked oxides.

The powerful topological Hall effect in this material not only advances the understanding of magnetic materials and interactions, but also offers potential for fundamental research and application explorations in spintronics, according to the team.