Canted Magnetization Research Articles

Bulk Cr tips with full spatial magnetic sensitivity for spin-polarized scanning tunneling microscopy

A full magnetic characterization of bulk Cr tips has been achieved using spin-polarized scanning tunneling microscopy at low temperature. A detailed bias-dependent study of the spatial magnetic sensitivity on the system of 1.5 monolayers of Fe/W(110) reveals that all magnetic directions in space are sensed over a wide bias range, thereby indicating a canted magnetization direction being a typical feature of bulk Cr tips. Consequently, using Cr as tip material allows any standard scanning tunneling microscope setup to be extended by the spin-polarized mode.

Thickness-driven polar spin reorientation transition in ultrathin Fe/Au(001) films

The magnetic properties of ultrathin Fe films grown on Au(001) were studied at room temperature as a function of iron thickness in the range of two to three Fe monolayers (ML). The magneto-optic Kerr effect (MOKE) indicated that a spin reorientation from an in-plane direction to the film normal direction takes place when the iron thickness is reduced from 2.3 to 2.0 ML. Values of the effective magnetic anisotropy constants were determined from MOKE and superconducting quantum interference device measurements. The flow analysis of the effective anisotropy constants in anisotropy space revealed that the transition occurs via an intermediate state of canted magnetization.

Two-magnon damping in thin films in case of canted magnetization: Theory versus experiment

We present results for ferromagnetic resonance measurements in ultrathin magnetic films. Our aim is to investigate quantitatively the damping of spin motions where different sources of damping are present. We investigate a polycrystalline 10-nm-thick Co film grown on GaAs using microwave frequencies between 4 and 24 GHz and different orientations of the static magnetic field. We discuss the role of Gilbert and two-magnon dampings (activated by defects in the film) within the theoretical framework presented some years ago by Arias and Mills [Phys. Rev. B 60, 7395 (1999)] and its extension to the case in which the magnetization is tipped out of the film plane [P. Landeros, R. E. Arias, and D. L. Mills, Phys. Rev. B 77, 214405 (2008)]. It is found that linewidth vs. field angle data are well reproduced by the theory for several frequencies and we obtain information about fundamental parameters as well as the role of defects in the dynamical response of the prototype Co system.

Time- and vector-resolved magneto-optical Kerr effect measurements of large angle precessional reorientation in a 2×2μm2 ferromagnet

The precessional dynamics of a 2×2μm2 CoFe∕NiFe (4.6nm) element stimulated by an in-plane pulsed magnetic field have been investigated using time- and vector-resolved Kerr microscopy measurements and micromagnetic simulations. The time-resolved signals were normalized to in-plane hysteresis loops obtained from the patterned material, and suggest that the magnetization reorients through an angle of 100°±10°. The simulations reveal that only the magnetization of the center region undergoes large angle reorientation, while the canted magnetization at the edges of the element remains pinned. An enhanced Gilbert damping parameter of 0.1 was required to reproduce the experimentally observed Kerr signals.

Cubic versus Spherical Magnetic Nanoparticles: The Role of Surface Anisotropy

The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, T(B), of the nanoparticles depends on their shape, with the spherical ones exhibiting larger T(B). Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects.

Imaging the Cone State of the Spin Reorientation Transition

The magnetization behavior and the domain pattern in remanence are studied in Co/Pt multilayers. The reorientation of magnetization from perpendicular to in plane is found to happen via the state of canted magnetization. In the transition from an easy axis to an easy plane a stable domain pattern in the in-plane magnetization components is found for Co/Pt multilayers. The analysis of the domain pattern reveals that the magnetization canting is such that all in-plane orientations of magnetization are equally occupied. The found structure is appointed to the cone state.

Spin reorientation transition and magnetic domain structure of Co ultrathin films grown on a faceted Au(455) surface

The spin reorientation transition (SRT) and magnetic domain structure of Co ultrathin films on faceted Au(455) surfaces have been investigated as a function of thickness by using magneto-optic Kerr effect and x-ray photoemission electron microscopy in combination with x-ray magnetic circular dichroism. The magnetization easy axis of the Co films is found to rotate from an out-of-plane to an in-plane orientation perpendicular to the atomic steps of the substrate due to the dominant contribution of the step-induced magnetic anisotropy. Moreover, magnetic stripe domains are observed to replicate the underlying periodic facets of the Au surface. Depending on the facet, the SRT occurs at a well-defined critical thickness and proceeds via a different mechanism: a state of uniform canted magnetization is formed for (233) facets, while the SRT involves continuous magnetization rotation followed by the nucleation of small in-plane magnetic domains for (677) facets.

Imaging the domain pattern of the canted magnetization state in Co/Pt multilayer films

The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern.

Magnetic canting or not? Two isomorphous 3D CoII and NiII coordination polymers with the rare non-interpenetrated (10,3)-d topological network, showing spin-canted antiferromagnetism only in the CoII system

The in situ solvothermal reaction of 3,4-dicyano-1,2,5-thiadiazole with MCl(2) (M = Co, Ni) and NaOH afforded two isomorphous complexes, [M2(L)2(H(2)O)2]n (L = 2,1,3-thiadiazole-4,5-dicarboxylate), which exhibit a rare non-interpenetrated (10,3)-d (utp) network topology and interesting magnetic behaviors: spin-canted antiferromagnetism for the Co(II) complex, but simple antiferromagnetic coupling for the Ni(II).

Adatom-induced spin reorientation transitions and spin canting in Co films on a stepped Cu(001) surface

We have investigated spin reorientation transitions on ultrathin Co films grown on a stepped Cu(1 1 17) surface upon adsorption of Ag and NO by means of the magneto-optical Kerr effect, the magnetization-induced second harmonic generation, x-ray magnetic circular dichroism, and laser excited photoemission magnetic circular dichroism. Although a spin reorientation transition from the step parallel to perpendicular direction is well known to occur after Ag deposition, the magnetization after the transition is found to be canted from the film plane toward the terrace atomic plane. On the other hand, upon NO adsorption, the Co film is shown to lose its inherent twofold uniaxial magnetic anisotropy without showing canted magnetization.

Chiral Molecular Magnets: Synthesis, Structure, and Magnetic Behavior of the Series [M(L‐tart)] (M = MnII, FeII, CoII, NiII; L‐tart = (2R,3R)‐(+)‐tartrate)

A new series of layered magnets with the formula [M(L-tartrate)] (M = Mn(II), Co(II), Fe(II), Ni(II); L-tartrate = (2R,3R)-(+)-tartrate) has been prepared. All of these compounds are isostructural and crystallize in the chiral orthorhombic space group I222, as found by X-ray structure analysis. Their structure consists of a three-dimensional polymeric network in which each metal shows distorted octahedral coordination bound to four L-tartrate ligands, two of which chelate through an alcohol and a carboxylate group and the other two bind terminally through a monodentate carboxylate group. The chirality of the ligand imposes a Delta conformation on all metal centers. Magnetically, the paramagnetic metal centers form pseudotetragonal layers in which each metal is surrounded by four other metals, with syn,anti carboxylate bridges. These salts show intralayer antiferromagnetic or ferromagnetic interactions, depending on the electronic configuration of the metal, and weak interlayer antiferromagnetic interaction. In all cases the magnetic properties are strongly affected by the anisotropy of the system, and the presence of magnetic canting has been found. The Mn derivative behaves as a weak ferromagnet with a critical temperature of 3.3 K. The Ni derivative shows very unusual magnetic behavior in that it exhibits antiferromagnetic ordering below 6 K, the onset of spontaneous magnetization arising from spin reorientation into a canted phase below 4.5 K, and a field-induced ferromagnetic state above 0.3 T at 2 K, behavior typical of metamagnets. The Fe and Co derivatives show antiferromagnetic interactions between spin carriers, but do not order above 2 K.

Mössbauer and magnetic study of Mn2+- and Cr3+-substituted spinel magnesioferrites of the composition Mg1−xMnxFe2−2xCr2xO4

Chromium and manganese co-substituted spinel magnesioferrites of the composition Mg1−x Mn x Fe2−2 x Cr2x O4 (x=O.O, 0.1, 0.2, 0.3, and 0.5) were investigated with X-ray diffraction (XRD), Mossbauer spectroscopy and magnetic measurements. The cation distribution inferred suggests that Mn2+ and Cr3+ ions dominantly occupy the A- and Bsites respectively. The gradual decrease of the hyperfine fields and Curie temperatures with increasing x reflects a gradual weakening in the AB exchange interaction. Mossbauer data of the sample with x=0.5 is suggestive of cation clustering and/or superparamagnetism. The magnetization data is suggestive of Yafet-Kittel-type canted magnetism.

Abnormal reduction of coercivity on magnetic cobalt–platinum alloy films

Ultrathin Co–Pt alloy films as substrate were studied by the surface magneto-optical Kerr effect. As the growth of Ni, the films show uniquely high polar Kerr responses without any in-plane signals. The coercivity decreased until the thickness of Ni film was higher than 5 ML. A new surface structure was discovered at 7–10 ML Ni/Co–Pt films by the low-energy electron diffraction. Interestingly, polar Kerr signal and coercivity of the 10 ML Ni/Co–Pt(1 1 1) template film reduced rapidly as Co films were further deposited onto only about 1–2 ML. Then the films show a canted magnetization with a rollback hysteresis in the polar configuration during the growth of Co. Coercivity of the 7 ML Co/Ni/Co–Pt film was found unusually down to almost 100 Oe.The corresponding magic number at around 7 ML of Co in the abnormal reduction of coercivity may be attributed to the cluster formations of Co.

Ab initio study of canted magnetism of finite atomic chains at surfaces

By using ab initio methods on different levels we study the magnetic ground state of(finite) atomic wires deposited on metallic surfaces. A phenomenological model based onsymmetry arguments suggests that the magnetization of a ferromagnetic wire is alignedeither normal to the wire and, generally, tilted with respect to the surface normal orparallel to the wire. From a first-principles point of view, this simple model canbe best related to the so-called magnetic force theorem calculations being oftenused to explore magnetic anisotropy energies of bulk and surface systems. Thesecond theoretical approach that we use to search for the canted magnetic groundstate is the first-principles adiabatic spin dynamics technique extended to thecase of fully relativistic electron scattering. First, for the case of two adjacent Featoms on a Cu(111) surface we demonstrate that the reduction of the surfacesymmetry can indeed lead to canted magnetism. The anisotropy constants andconsequently the ground state magnetization direction are very sensitive to the positionof the dimer with respect to the surface. We also performed calculations for aseven-atom Co chain placed along a step edge of a Pt(111) surface. As far as theground state spin orientation is concerned, we obtain excellent agreement withexperiment. Moreover, the magnetic ground state turns out to be slightly non-collinear.

Antiferromagnetic Resonance inLaMnO3at Low Temperature

The antiferromagnetic resonance modes have been studied on a stoichiometric single crystal of ${\mathrm{L}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{O}}_{3}$ well below the N\'eel temperature, with a static magnetic field along all three crystallographic directions. A canted antiferromagnet model, with biaxial anisotropy and a Dzyaloshinski-Moriya (DM) interaction, explains the results. The DM interaction, often cited as the dominant cause of the canted magnetism, is found to be weak. Instead, the ${\mathrm{G}\mathrm{d}\mathrm{F}\mathrm{e}\mathrm{O}}_{3}$-type octahedron rotation leads to the tilted character of the single-ion anisotropy that plays a dominant role in spin canting.

Surface magnetic canting in a nonuniform film*1

The zero temperature equilibrium configuration of a nonuniform system made of a ferromagnetic (FM) monolayer on top of a semi-infinite FM film is calculated using a nonlinear mapping formulation of mean-field theory, where the surface is taken into account via an appropriate boundary condition. The analytical criterion for the existence of surface magnetic canting, previously obtained by Popov and Pappas, is also recovered.

Surface magnetic canting in a nonuniform film

Abstract The zero temperature equilibrium configuration of a nonuniform system made of a ferromagnetic (FM) monolayer on top of a semi-infinite FM film is calculated using a nonlinear mapping formulation of mean-field theory, where the surface is taken into account via an appropriate boundary condition. The analytical criterion for the existence of surface magnetic canting, previously obtained by Popov and Pappas, is also recovered.

Fabrication of L10 ordered FePt thin films with a canted easy magnetization axis on MgO (1 1 0) substrate

Abstract We have investigated the magnetic properties of highly coercive FePt films prepared on both MgO (0 0 1) and MgO (1 1 0) substrates with various film thicknesses ( t N ). FePt (0 0 1) films with perpendicular magnetization and FePt (1 0 1) films with a canted easy magnetization axis ( c -axis) were prepared on MgO (0 0 1) and MgO (1 1 0) substrates, respectively. At the critical thickness, where the film morphology changes from a particulate to a continuous state, a drastic decrease in the coercivity H c has been observed for the FePt (0 0 1) film, while no jump of H c has been observed for the FePt (1 0 1) films.

Dimerization versus orbital-moment ordering in a Mott insulator YVO3.

We use exact diagonalization combined with mean-field theory to investigate the phase diagram of the spin-orbital model for cubic vanadates. The spin-orbit coupling competes with Hund's exchange and triggers a novel phase, with the ordering of t(2g) orbital magnetic moments stabilized by the tilting of VO6 octahedra. It explains qualitatively spin canting and reduction of magnetization observed in YVO3. At finite temperature, an orbital instability in the C-type antiferromagnetic phase induces modulation of magnetic exchange constants even in the absence of lattice distortions. The calculated spin structure factor shows a magnon splitting at q-->=(0,0,pi / 2) due to the orbital dimerization.

In situ ferromagnetic resonance in coupled ultrathin trilayers with perpendicularly orientedeasy axes

Ultrathin ferromagnetic trilayers with perpendicularly oriented easy axes—one filmin-plane the other out-of-plane—attracted recent interest in the study of interlayerexchange coupling, domain formation, and canted magnetization orientation. To investigateand understand the thermodynamic ground state of such a prototype trilayer we employedin situ ferromagnetic resonance (FMR) for a Ni/Cu/Co/Cu(001) trilayer. The FMR polarangular dependence has been measured and analysed in the framework of theLandau–Lifshitz equation. In addition the thickness of the Cu spacer layer has beenchanged to manipulate the strength of the interlayer exchange coupling and select betweenferromagnetic and antiferromagnetic coupling. The FMR experiment yields—unlike othertechniques—the coupling strength and anisotropy energy in absolute energy units.This gives also a full insight into all the parameters governing the ground statefree energy, the equilibrium angles of the canted magnetization, as well as theoptical and acoustical mode formed by the two uniform spin-wave excitations.