Current driven magnetization dynamics in ferromagnets and antiferromagnets

The development of spintronics and potential applications demands a thorough understanding of various novel phenomena in ferromagnets and antiferromagnets. Magnetotransport measurements, which have been implemented in current data storage and magnetoresistive sensing technology, provide convenient and powerful approach to the characterizations of magnetism. We conduct point-contact magnetotransport investigations in metallic magnetic multilayers and antiferromagnetic insulators, aiming at probing the electron transports associated with local magnetic properties in those different materials. For metallic exchange biased spin valves, both radiofrequency (rf) and dc currents are injected through point contacts and we detect the rectified electrical signals. Point contacts with contact sizes of the order of 10-100 nm allow to probe the spins in very local scale. It is found that both linear ferromagnetic resonance and nonlinear parametric resonance can be observed driven by oscillating currents. Particularly, the parametric excitation driven by ac spin transfer torque (STT) is a promising candidate of techniques for realizing fast magnetic switching in spin torque based devices. As for investigating the single crystals of antiferromagnetic Mott insulator Sr₂IrO₄ (SIO), a large anisotropic magnetoresistance (AMR) signal originated from the entanglement of orbital physics and magnetic moments was revealed, shedding lights into the unexplored physics in heavy transition metal oxides in presence of comparable magnitudes of electron correlations and spin-orbit coupling. The crystalline AMR found in SIO may point out a practical path to the sensing of antiferromagnetic order in future AFM-based devices. Furthermore, detailed point-contact study of the electron transport in SIO under high electric biases discovers an electrically tunable transport band gap in this iridate, suggesting a very interesting playground for developing functional devices based on transition metal oxides.