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We present a direct observation of a flipping magnetization of a uniform Fe film/wedged-Mn bilayer induced by a biquadratic-type exchange coupling established at the interface. The element-resolved magnetic imaging shows that the Fe film exhibited a flipping of magnetization between the [&1horbar00] and [010] directions with a periodicity of one monolayer Mn thickness as below a critical temperature. The enhancement of the variation angle with the increase of Mn thickness follows the tendency of the finite-size effect of antiferromagnetism on interface exchange coupling. The flipping magnetization emerging coincidentally with the uncompensated-compensated transition of Mn magnetic surface indicates a frustration-induced biquadratic-type interface exchange coupling, and suggests a layered-like uncompensated AFM ordering for the Mn layer. [ABSTRACT FROM AUTHOR]

A textured thin film of FeGe was grown by magnetron sputtering with a helimagnetic ordering temperature of TN = 276 ± 2 K. From 5 K to room temperature, a variety of scattering processes contribute toward the overall longitudinal and Hall resistivities. These were studied by combining magnetometry and magnetotransport measurements. The high-field magnetoresistance (MR) displays three clear temperature regimes: Lorentz force MR dominates at low temperatures, above T ≈80 K scattering from spin-waves predominates, while finally for T ≳ 200 K scattering from fluctuating local moments describes the MR. At low fields, where the magnetization is no longer technically saturated, we find a scaling of magnetoresistance with the square of the magnetization, indicating that the MR due to the unwinding of spins in the conical phase arises from a similar mechanism to that in magnetic domain walls. This MR is only visible up to a temperature of about 200 K. Nofeatures can be found in the temperature or field dependence of the longitudinal resistivity that belie the presence of the underlying magnetic phase transition at TN: the marked changes in behavior are at much lower temperatures. The anomalous Hall effect has a dramatic temperature dependence in which the anomalous Hall resistivity scales quadratically with the longitudinal resistivity: comparison with anomalous Hall scaling theory shows that our system is in the intrinsic "moderately dirty" regime. Lastly, we find evidence of a topological Hall effect of size ∼100 μΩ cm. [ABSTRACT FROM AUTHOR]

We study the edge magnetization and the local density of states of chiral graphene nanoribbons using a π-orbital Hubbard model in the mean-field approximation. We show that the inclusion of a realistic next-nearest hopping term in the tight-binding Hamiltonian changes the graphene nanoribbon band structure significantly and affects its magnetic properties. We study the behavior of the edge magnetization upon departing from half-filling as a function of the nanoribbon chirality and width. We find that the edge magnetization depends very weakly on the nanoribbon width, regardless of chirality as long as the ribbon is sufficiently wide. We compare our results to recent scanning tunneling microscopy experiments reporting signatures of magnetic ordering in chiral nanoribbons and provide an interpretation for the observed peaks in the local density of states, that does not depend on the antiferromagnetic interedge interaction. [ABSTRACT FROM AUTHOR]

We report the manipulation of nitrogen vacancy (NV) spins in diamond when a nearby ferrimagnetic insulator, yttrium iron garnet, is driven into precession. The change in NV spin polarization, as measured by changes in photoluminescence, is comparable in magnitude to that from conventional optically detected magnetic resonance, but relies on a distinct mechanism as it occurs at a microwave frequency far away from the magnetic resonance frequency of the NV spin. This observation presents an approach to transferring ferromagnetic spin information into a paramagnet and then transducing the response into a robust optical signal. It also opens strategies for studying ferromagnetism and spin transport at the nanoscale. [ABSTRACT FROM AUTHOR]

Dynamic magnetization reversal in the mesofrequency range is studied by ac magneto-optical Kerr effect (ac-MOKE) and ac anisotropic magnetoresistance (ac-AMR) magnetometry in a series of epitaxial and polycrystalline thin magnetic films. The dynamic coercive field was found to scale as a power law with scaling exponents ≤1/2 depending on the ferromagnetic material. In addition, there is a low sweep rate regime in which the dynamic coercivity reaches a minimum. These findings are explained in the context of reversal proceeding by motion of a few domain walls (~1). At dc and low field sweep rates the reversal proceeds between local pinning sites via Barkhausen avalanches and the overall reversal speed is strongly dependent on the field sweep rate. At higher field sweep rates a continuous motion regime is entered in which the reversal velocity depends linearly on the applied field sweep rate and only an average pinning force is experienced by the wall. The fit of the dynamic coercivity vs applied field sweep rate allows the determination of the average nonlocal pinning field. The nonuniversal scaling exponent can be explained using recently developed models and introducing a field rate-dependent number of active domain walls. [ABSTRACT FROM AUTHOR]

The magnetization reversal process within the first two iron layers at the Fe/GaAs(001) interface is found to be different and independent from the Fe thin film bulk as measured by magnetic second-harmonic generation and magneto-optical Kerr effect. The interface magnetization is largely noncollinear from the bulk with an abrupt magnetic boundary and an anisotropic exchange coupling stiffness, weak interlayer coupling but relatively strong intralayer stiffness. In contrast, Fe/GaAs(l 10) exhibits a rigid coupling between interface and bulk magnetization suggesting that the interfacial bonding structure can dramatically change the nature of the exchange coupling. Moreover, the uniaxial magnetic anisotropy in Fe/GaAs(001) extends from the interface to the first 5 nm in the Fe film and is induced by stress. These results are also relevant to other magnetic/nonmagnetic interfaces with abrupt chemical bond structures. [ABSTRACT FROM AUTHOR]

All-electrical spin-wave spectroscopy and frequency-resolved magneto-optical Kerr-effect measurements are combined to study spin waves propagating through a magnetic antidot lattice nanopatterned from a Ni80Fe20 thin film. Spin waves are injected from a plain film into the antidot lattice and the transmission across the interface is explored in detail for different wavelengths. We find that spin waves with a wavelength much greater than the lattice periodicity are not described well by recently discussed approaches. Instead the spin-wave dispersion is consistent with an effective magnetization smaller than the saturation magnetization measured on the unstructured ferromagnetic material. Consistently, we find that the transmission coefficients are modeled well by assuming an effectively continuous metamaterial for spin waves characterized by the reduced magnetization. The experimental data and interpretation are substantiated theoretically using the plane-wave method and micromagnetic modeling. The results are interesting for the development of frequency-selective mirrors in magnonics through lateral nanopatterning. [ABSTRACT FROM AUTHOR]

The spin dependence of the photoelectron tunnel current from free-standing GaAs films into out-of-plane magnetized cobalt films is demonstrated. The measured spin asymmetry (A), resulting from a change in light helicity, reaches ±6% around zero applied tunnel bias and drops to ±2% at a bias of -1.6 V applied to the GaAs. This decrease is a result of the drop in the photoelectron-spin polarization that results from a reduction in the GaAs surface-recombination velocity. The sign of A changes with that of the cobalt magnetization. In contrast, A is negligible on nonmagnetic gold films. [ABSTRACT FROM AUTHOR]

Using x-ray photoemission electron microscopy and the magneto-optical Kerr effect, we have demonstrated a perpendicular magnetic anisotropy that could be due to exchange coupling between the ferromagnetic and antiferromagnetic layers. The results of magnetic imaging and hysteresis loops show that the magnetization of Fe and permalloy (Py) films orients from the in-plane to perpendicular direction, as an Mn underlayer is above a threshold value that depends on the Fe or Py layer thickness. Their thickness-dependent behaviors can be quantitatively described by a phenomenological model that takes into account the finite-size effect of the antiferromagnet on exchange coupling. The anisotropy energy extracted from the model and the thermal stability of perpendicular magnetization enhanced with the increase of the Mn underlayer further demonstrate the exchange coupling nature. [ABSTRACT FROM AUTHOR]