Abstract
Antiferromagnets (AFMs) are widely believed to be superior than ferromagnets in spintronics because of their high stability due to the vanishingly small stray field. It is thus expected that the order parameter of AFM should always align along the easy-axis of the crystalline anisotropy. In contrast to this conventional wisdom, we find that the AFM order parameter switches away from the easy-axis below a critical anisotropy strength when an AFM is properly tailored into a nano-structure. The switching time first decreases and then increases with the damping. Above the critical anisotropy, the AFM order parameter is stable and precesses under a microwave excitation. However, the absorption peak is not at resonance frequency even for magnetic damping as low as 0.01. To resolve these anomalies, we first ascertain the hidden role of dipolar interaction that reconstructs the energy landscape of the nano-system and propose a model of damped non-linear pendulum to explain the switching behavior. In this framework, the second anomaly appears when an AFM is close to the boundary between underdamped and overdamped phases, where the observed absorption lineshape has small quality factor and thus is not reliable any longer. Our results should be significant to extract the magnetic parameters through resonance techniques.
Highlights
Ferromagnets played a vital role in the early development of magnetism, as well as modern spintronics, while studies and applications of antiferromagnets (AFMs) are quite limited due to their lack of tunability and are useless
magnetostatic interaction (MI) naturally exists in experiments, and one should be very careful to explain the experimental data by the theory without MI effects, especially when extracting the anisotropy coefficients
Even though the total magnetic charges of an AFM as well as the resulting magnetostatic field outside the system are vanishingly small, the local charge distribution at the atomic scale could considerably modify the system anisotropy in magnetic nanowires as well in quasi-2D and -3D structures
Summary
Ferromagnets played a vital role in the early development of magnetism, as well as modern spintronics, while studies and applications of antiferromagnets (AFMs) are quite limited due to their lack of tunability and are useless. In the past few years, AFMs have started to attract significant attention after the discovery of an electrical knob to control antiferromagnetic order in a class of antiferromagnets with broken inversion symmetry [1,2] Various aspects, such as a damping mechanism [3,4], spin transfer torque [5,6,7,8], magnetic switching [1], spin pumping [9], and domain-wall/skyrmion dynamics [10,11,12,13,14,15,16,17,18,19], have been extensively investigated.
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