2023, Tschirner, Teresa, Keßler, Philipp, Gonzalez Betancourt, Ruben Dario, Kotte, Tommy, Kriegner, Dominik, Büchner, Bernd, Dufouleur, Joseph, Kamp, Martin, Jovic, Vedran, Smejkal, Libor, Sinova, Jairo, Claessen, Ralph, Jungwirth, Tomas, Moser, Simon, Reichlova, Helena, Veyrat, Louis

Observations of the anomalous Hall effect in RuO2 and MnTe have demonstrated unconventional time-reversal symmetry breaking in the electronic structure of a recently identified new class of compensated collinear magnets, dubbed altermagnets. While in MnTe, the unconventional anomalous Hall signal accompanied by a vanishing magnetization is observable at remanence, the anomalous Hall effect in RuO2 is excluded by symmetry for the Néel vector pointing along the zero-field [001] easy-axis. Guided by a symmetry analysis and ab initio calculations, a field-induced reorientation of the Néel vector from the easy-axis toward the [110] hard-axis was used to demonstrate the anomalous Hall signal in this altermagnet. We confirm the existence of an anomalous Hall effect in our RuO2 thin-film samples, whose set of magnetic and magneto-transport characteristics is consistent with the earlier report. By performing our measurements at extreme magnetic fields up to 68 T, we reach saturation of the anomalous Hall signal at a field Hc ≃ 55 T that was inaccessible in earlier studies but is consistent with the expected Néel-vector reorientation field.

2022, Song, Qi, Sun, Jiaxin, Parzyck, Christopher T., Miao, Ludi, Xu, Qing, Hensling, Felix V. E., Barone, Matthew R., Hu, Cheng, Kim, Jinkwon, Faeth, Brendan D., Paik, Hanjong, King, Phil D. C., Shen, Kyle M., Schlom, Darrell G.

Utilizing the powerful combination of molecular-beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES), we produce and study the effect of different terminating layers on the electronic structure of the metallic delafossite PdCoO2. Attempts to introduce unpaired electrons and synthesize new antiferromagnetic metals akin to the isostructural compound PdCrO2 have been made by replacing cobalt with iron in PdCoO2 films grown by MBE. Using ARPES, we observe similar bulk bands in these PdCoO2 films with Pd-, CoO2-, and FeO2-termination. Nevertheless, Pd- and CoO2-terminated films show a reduced intensity of surface states. Additionally, we are able to epitaxially stabilize PdFexCo1-xO2 films that show an anomaly in the derivative of the electrical resistance with respect to temperature at 20 K, but do not display pronounced magnetic order.