Probing the surface magnetism of antiferromagnets*

Using antiferromagnet-ferromagnet spin valves, we detected and studied uncompensated magnetization at the boundary of an antiferromagnetic FeF₂(110) layer at different temperatures and magnetic fields. It was discovered that, at low temperatures, this magnetization possesses unprecedented stability, and cannot be reversed even in very high magnetic fields (> 90 kOe). Our experimental technique allowed to detect and characterize the reversal of the boundary magnetization at temperatures close to the Néel temperature, thus, demonstrating the possibility of isothermal imprinting of pining into the antiferromagnet. The boundary magnetization was detected only for the valves with the FeF₂(110) layer and not for the valves containing FeF₂(100) or FeF₂(001). This observation is consistent with symmetry-related theory predicting magnetization at the surface of antiferromagnets with broken time-reversal symmetry. We will show and discuss the experimental results on the valves containing antiferromagnetic Mn₂Au whose spin structure can be manipulated electrically.