Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition

We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.Copyright (2014) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters (volume 105: 092408) and may be found at http://scitation.aip.org/content/aip/journal/apl/105/9/10.1063/1.4895032

A robust soliton ratchet using combined antiferromagnetic and ferromagnetic interlayer couplings

A sharp magnetic soliton can be created and propagated in a vertical ratchet structure based on magnetic layers with out-of-plane anisotropy using a combination of antiferromagnetic and ferromagnetic interlayer couplings. This allows the use of identical magnetic layers in the stack, which simplifies the implementation of the ratchet compared to schemes which use alternating layer thicknesses. The ratchet behavior is analyzed using an Ising-macrospin approximation and conditions are derived for the propagation of a soliton, which is demonstrated experimentally. Values extracted from the experimental data for the coercivities and interlayer couplings show significant variation, which demonstrates the robustness of the soliton propagation.This research was funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN. R.L. acknowledges support from the Netherlands Organization for Scientific Research (VENI 68047428). A.F.-P. acknowledges an EPSRC Early Career fellowship and support from the Winton Programme for the Physics of Sustainability.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.491401

Evidence for phonon skew scattering in the spin Hall effect of platinum

\u3cp\u3eWe measure and analyze the effective spin Hall angle of platinum in the low-residual resistivity regime by second-harmonic measurements of the spin-orbit torques for a multilayer of Pt|Co|AlOx. An angular-dependent study of the torques allows us to extract the effective spin Hall angle responsible for the damping-like torque in the system. We observe a strikingly nonmonotonic and reproducible temperature dependence of the torques. This behavior is compatible with recent theoretical predictions which include both intrinsic and extrinsic (impurities and phonons) contributions to the spin Hall effect at finite temperatures.\u3c/p\u3

Spin polarized electron tunneling

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Racetrack memory based on in-plane-field controlled domain-wall pinning

Magnetic domain wall motion could be the key to the next generation of data storage devices, shift registers without mechanically moving parts. Various concepts of such so-called ‘racetrack memories’ have been developed, but they are usually plagued by the need for high current densities or complex geometrical requirements. We introduce a new device concept, based on the interfacial Dzyaloshinskii-Moriya interaction (DMI), of which the importance in magnetic thin films was recently discovered. In this device the domain walls are moved solely by magnetic fields. Unidirectionality is created utilizing the recent observation that the strength with which a domain wall is pinned at an anisotropy barrier depends on the direction of the in-plane field due to the chiral nature of DMI. We demonstrate proof-of-principle experiments to verify that unidirectional domain-wall motion is achieved and investigate several material stacks for this novel device including a detailed analysis of device performance for consecutive pinning and depinning processes

Canted states in anti-ferromagnetically coupled magnetic bilayers

Bilayer systems of ultra-thin anti-ferromagnetically coupled Co and CoFeB layers have been systematically investigated. The intention was to find systems in which the mag- netization of one of the layers (or both) would be in a canted state, meaning that the magnetization is neither in-plane nor out-of-plane at remanence. We have indeed been successful in obtaining such systems, observing configurations where one layer is out-of- plane and one is canted, and others where one layer is in-plane and one is canted. In this work we will discuss other phenomena that have been observed, such as the presence of an in-plane bias field or the competition between the switching fields of both layers as a function of the sweeping field rate

Magnetic behavior of the diluted magnetic semiconductor Zn1-xMnxSe

The magnetic susceptibility and specific heat of the diluted magnetic semiconductor Zn1-xMnxSe have been measured in the temperature range 10 m

Hyperfine field distribution in the Heusler compound Co2FeAl probed by 59Co nuclear magnetic resonance

The Heusler compound Co2FeAl is reported to occur in various structures ranging from the completely ordered L21 to the completely disordered A2 structure type. In this work, we use spin echo nuclear magnetic resonance (NMR) to probe the local structure of Co2FeAl bulk samples. The study of Co2FeAl bulk samples provides the unique possibility to verify the intrinsic generic structural properties. The 59Co NMR measurements reveal a distribution of Fe and Al not only in the first neighbouring shells of the 59Co nuclei but also in more distant shells. The analysis of 59Co NMR main resonance lines with an underlying sub-structure confirms that the local structure of the as-cast Co2FeAl bulk samples consists of a B2 type structure with contributions of the L21 type structure of about 10%. The observed sub-lines, which are attributed to a distribution of Fe and Al atoms in more distant shells, were previously not resolved in NMR spectra of Co2FeAl thin films, pointing to better long range order in bulk material than in thin films. We also show that the individual contributions of the structure types can be influenced by annealing

Tunable resistivity of individual magnetic domain walls

Despite the relevance of current-induced magnetic domain wall (DW) motion for new spintronics applications, the exact details of the current-domain wall interaction are not yet understood. A property intimately related to this interaction is the intrinsic DW resistivity. Here, we investigate experimentally how the resistivity inside a DW depends on the wall width ¿, which is tuned using focused ion beam irradiation of Pt/Co/Pt strips. We observe the nucleation of individual DWs with Kerr microscopy, and measure resistance changes in real time. A 1/¿2 dependence of DW resistivity is found, compatible with Levy-Zhang theory. Also quantitative agreement with theory is found by taking full account of the current flowing through each individual layer inside the multilayer stack