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We determine the composition of intrinsic as well as extrinsic contributions to the anomalous Hall effect (AHE) in the isoelectronic L1_{0} FePd and FePt alloys. We show that the AHE signal in our 30 nm thick epitaxially deposited films of FePd is mainly due to an extrinsic side jump, while in the epitaxial FePt films of the same thickness and degree of order the intrinsic contribution is dominating over the extrinsic mechanisms of the AHE. We relate this crossover to the difference in spin-orbit strength of Pt and Pd atoms and suggest that this phenomenon can be used for tuning the origins of the AHE in complex alloys.

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A magnetic helix realizes a one-dimensional magnetic crystal with a period given by the pitch length λ h . Its spin-wave excitations -the helimagnons -experience Bragg scattering off this periodicity leading to gaps in the spectrum that inhibit their propagation along the pitch direction. Using high-resolution inelastic neutron scattering the resulting band structure of helimagnons was resolved by preparing a single crystal of MnSi in a single magnetic-helix domain. At least five helimagnon bands could be identified that cover the crossover from flat bands at low energies with helimagnons basically localized along the pitch direction to dispersing bands at higher energies. In the low-energy limit, we find the helimagnon spectrum to be determined by a universal, parameterfree theory. Taking into account corrections to this low-energy theory, quantitative agreement is obtained in the entire energy range studied with the help of a single fitting parameter.PACS numbers: 75.30. Ds, 78.70.Nx, 71.27.+a, 71.70.Gm The weak spin-orbit Dzyaloshinskii-Moriya interaction, D, in the cubic chiral magnets energetically favours spatial modulations of the magnetization. This gives rise to magnetic crystalline phases with unit cells that are incommensurate with and much larger than the atomic lattice spacing. Most prevalent is the magnetic helix, a one-dimensional magnetic crystal, with a large pitch λ h = 2π/k h proportional to the ratio J/D where J is the magnetic exchange [1]. For a small range of finite magnetic fields, a two-dimensional magnetic crystal is also stabilized close to the critical temperature [2]. It can be identified as a lattice of magnetic skyrmions whose non-trivial topology is at the origin of various interesting phenomena [3] like, for example, a topological Hall effect [4,5] and an emergent electrodynamics [6,7]. Interestingly, the phase transition from the paramagnetic to the magnetically ordered phases at small fields corresponds to a weak crystallization process [8] and is driven firstorder by strongly correlated chiral paramagnons [9][10][11].The spin-wave excitations of these magnetic crystals possess a band structure ω n,q with band index n that, according to Bloch's theorem, reflects the periodicity of the magnetic order. For the magnetic helix with a pitch vector k h , the dispersion is periodic, ω n,q = ω n,q+mk h with m ∈ Z, along the direction in momentum space singled out by k h . In contrast to commensurate antiferromagnets, however, the size k h = |k h | of the resulting magnetic Brillouin zone is small; for MnSi at lowest temperatures λ h = 180Å and k h = 0.035Å −1 . Importantly, this ensures on the one hand that the dispersion, ω n,q , of the magnons is universal in the sense that it is captured by an effective continuum theory and is determined by only a few parameters. On the other hand, a high resolution of momenta is required in order to resolve the band structure experimentally with the help of inelastic neutron scattering. In a first experiment on MnSi, Janoschek et al. [12] succee...

Preparation of giant magnetostrictive thin film by magnetron and ion beam sputtering processes Rev. Sci. Instrum. 71, 996 (2000)

An angle dependent analysis of the planar Hall effect (PHE) in nanocrystalline single-domain Co 60 Fe 20 B 20 thin films is reported. In a combined experimental and theoretical study we show that the transverse resistivity of the PHE is entirely driven by anisotropic magnetoresistance (AMR). Our results for Co 60 Fe 20 B 20 obtained from first principles theory in conjunction with a Boltzmann transport model take into account the nanocrystallinity and the presence of 20 at. % boron. The ab initio AMR ratio of 0.12% agrees well with the experimental value of 0.22%. Furthermore, we experimentally demonstrate that the anomalous Hall effect contributes negligibly in the present case. DOI: 10.1103/PhysRevLett.107.086603 PACS numbers: 72.25.Ba, 71.70.Ej, 72.15.Gd Electron transport effects employing the electronic spin degree of freedom lie at the heart of spintronics and its applications not only in information technology [1] but more increasingly also in sensorics for biomedical purposes, where the utmost sensitivity for detecting minute magnetic stray fields is needed. The planar Hall effect (PHE) and the anomalous Hall effect (AHE) as well as tunneling magnetoresistance are promising phenomena for realizing highly sensitive sensors. From a materials point of view, nanocrystalline Co 60 Fe 20 B 20 (CoFeB) attracts growing attention since it combines large saturation magnetization with low coercivity [2,3], both favoring high sensitivities.PHE and AHE are both observed as a voltage transverse to the applied current [4,5] in contrast to the anisotropic magnetoresistance (AMR), which is measured in the longitudinal geometry. For PHE the magnetization M lies in the plane spanned by the current density j ¼ je x and the direction e y of the transverse voltage measurement, and for AHE the component of M perpendicular to j and e y matters. Although AMR has been known since Thomson's-later known as Lord Kelvin-observations in 1856 [6], PHE was discovered only a century later in polycrystalline permalloy [7]. More recently, PHE has also been found in crystalline La 2=3 Fe 1=3 MnO 3 [8] and as a very large effect at low temperatures in the dilute magnetic semiconductor (Ga,Mn)As [9]. The transverse resistance xy characterizing the PHE and the longitudinal resistivity xx denoting the AMR are given by [10] xy ¼ ð k À ? Þ sinÈ cosÈwhere k ( ? ) is the resistivity along (perpendicular to) the direction of the in-plane component of M, and È is the angle enclosed by j and M. A transverse voltage arises whenever the current is neither perpendicular nor parallel to the magnetization. Even though the AMR is a subtle spin-orbit effect, quantitatively reliable predictions from first principles based on the density functional theory (DFT) can be made [11,12]. In this Letter, we elucidate the role of AMR in the PHE in nanocrystalline Co 60 Fe 20 B 20 thin films experimentally and by ab initio calculations. We measure AMR and PHE in longitudinal and transverse four-probe transport experiments. The single-domain behavior enforced by an ...

The skyrmion crystal (SkX) characterized by a multiple-q helical spin modulation has been reported as a unique topological state that competes with the single-q helimagnetic order in noncentrosymmetric materials. Here we report the discovery of a rich variety of multiple-q helimagnetic spin structures in the centrosymmetric cubic perovskite SrFeO 3 . On the basis of neutron diffraction measurements, we have identified two types of robust multiple-q topological spin structures that appear in the absence of external magnetic fields: an anisotropic double-q spin spiral and an isotropic quadruple-q spiral hosting a three-dimensional lattice of hedgehog singularities. The present system not only diversifies the family of SkX host materials, but furthermore provides an experimental missing link between centrosymmetric lattices and topological helimagnetic order. It also offers perspectives for integration of SkXs into oxide electronic devices.

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