Anomalous Hall effect in ferromagnetic LaCo₂As₂ and ferrimagnetic NdCo₂As₂

We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo₂As₂ and NdCo₂As₂. LaCo₂As₂ is a soft metallic ferromagnet which exhibits purely intrinsic anomalous Hall effect (AHE) due to Co-3d electrons. With Nd-4f electronic magnetism, ferrimagnetic NdCo₂As₂ manifests pronounced sign reversal and multiple hysteresis loops in temperature- and field-dependent magnetization, Hall resistivity, and magnetoresistance, due to complicated magnetic structural changes. We reveal that the AHE for NdCo₂As₂ is stemming from the Co sub-lattice and deduce its phase diagram which includes magnetic compensation and two meta-magnetic phase transitions. The sensitivity of the Hall effect on the details of the magnetic structures in ferrimagnetic NdCo₂As₂ provides a unique opportunity to explore the magnetic interaction between 4f and 3d electrons and its impact on the electronic structure.