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We study the high-temperature phase diagram of the chiral magnetic insulator Cu 2 OSeO 3 by measuring the spin-Hall magnetoresistance (SMR) in a thin Pt electrode. We find distinct changes in the phase and amplitude of the SMR signal at critical lines separating different magnetic phases of bulk Cu 2 OSeO 3 . The skyrmion lattice state appears as a strong dip in the SMR phase. A strong enhancement of the SMR amplitude is observed in the conical spiral state, which we explain by an additional symmetry-allowed contribution to the SMR present in noncollinear magnets. We demonstrate that the SMR can be used as an all-electrical probe of chiral surface twists and skyrmions in magnetic insulators.

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Recently, it has been shown that the chiral magnetic insulator Cu2OSeO3 hosts skyrmions in two separated pockets in temperature and magnetic field phase space. It has also been shown that the predominant stabilization mechanism for the low-temperature skyrmions (LTS) phase is the crystalline anisotropy in contrast to temperature fluctuations, which stabilize the well established high-temperature skyrmion (HTS) lattice. Here, we report on the gigahertz dynamics in the LTS phase in Cu2OSeO3. The LTS phase is populated via a field cycling protocol with the static magnetic field applied parallel to the h100i crystalline direction of plate and cuboid-shaped bulk crystals. By analyzing temperature-dependent broadband spectroscopy data, clear evidence of low-temperature skyrmion excitations with clockwise (CW), counterclockwise (CCW), and breathing mode (BR) character at temperatures below T = 40 K are shown. We find that the modes’ intensities can be tuned with the number of field-cycles below the saturation field, and by tracking the resonance frequencies, the LTS phase diagram can be established. From our experiments, we conclude that the LTS phase is well separated from the high-temperature phase. Furthermore, by monitoring the strength of the observed hybridization between a dark CW mode and the BR as a function of temperature for the two differently shaped crystals, we unambiguously conclude that the magnetocrystalline anisotropy governs the hybridization.

Current induced magnetization switching, jointly with the manipulation of exchange bias, via spin-orbit torques (SOT) on sub-nanosecond timescales hold great promise for fast and low-power spintronic devices. Speci cally, the time-resolved detection and subsequent analysis of switching trajectories relevant to ferromagnet/antiferromagnet exchange biased structures are central to designing SOT devices with high speed, and are still open questions. Here, we report the SOT-induced multileveled switching on sub-nanosecond timescales in Pt/Co/IrMn heterostructures, and illustrate the time-resolved magnetization switching trajectories of the exchange bias. By adopting time-resolved magneto-optical Kerr microscopy combined with micromagnetic simulations, our work reveals that not only the ferromagnets, but also the multiple antiferromagnetic domains and exchange bias, can be partially switched by sub-nanosecond current pulse, to exibly control the switching probabilities at multiple levels. The experiments demonstrate that the SOT switching of exchange bias, which immediately depends on the current density, can signi cantly stabilize the multileveled magnetization switching within sub-nanosecond current pulse with high thermal stability. Main TextSpintronic devices based on spin-orbit torques (SOT) have emerged as crucial candidates for future nonvolatile memory devices with low power consumption and high operation speed 1-3 . Developed from the initial SOT devices comprising heavy metal/ferromagnet (FM)/Oxide trilayers 4,5 , the introduction of FM/antiferromagnet (AFM) structures with in-plane exchange bias has extra bene ts. In addition to the advantage of inducing an internal effective eld through the exchange bias effect to enable eld-free SOT switching 6-8 , a second bene t is that optimized structures also provide a exible approach to manipulate the AFM spins through energy-e cient SOT switching 9,10 . The reversal of FM accompanied by the switching of exchange bias also has technological importance for realizing robust magnetization switching with high thermal stability. In view of the intrinsic high frequency response of AFMs 11,12 , gaining insight into the magnetization dynamics as well as into the time-resolved switching process of SOT devices comprising FM/AFM is of great interest, since this lays the scienti c foundation for designing SOT devices with ultrafast switching speed.Recent studies have shown that the perpendicular exchange bias at FM/AFM interfaces can be switched by SOTs, which are either generated from the heavy metal Pt in Pt/Co/IrMn 9 , or from the AFM IrMn in IrMn/CoFeB 10 . The independent manipulation of the perpendicular magnetization and the interfacial exchange bias in the FM/AFM system could improve the plasticity and stability of potential devices towards practical applications. However, these recent experiments have focused on examining the nal magnetic state long after a current pulse has passed, while investigations of the details of magnetization dynamics and in particular the tim...