Long range magnetic ordering with giant magnetic moments in Pt doped NiMn thin films (original) (raw)
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Three-dimensional numerical simulation of equilibrium micromagnetic configurations existing in thin ferromagnetic films with surface anisotropy is carried out taking into account the strong demagnetization field acting on the film magnetization and the true micromagnetic boundary condition on the film surface. The numerical results are obtained in the simplest N eel approximation for surface anisotropy energy, a surface anisotropy constant K s being a single phenomenological parameter. It is found that the spin canted state has the lowest total energy as compared to various multi-domain configurations in the intermediate range of thickness, L z,min < L z < L z,max , if the magnitude of surface anisotropy constant K s is below a certain critical value. For small thickness, L z < L z,min , the film is perpendicular magnetized, whereas for a thicker film, L z > L z,max , nearly uniform in-plane magnetization, or the vortex has been obtained depending on the film in-plane aspect ratio. On the other hand, different labyrinth domain structures with large in-plane magnetization have been calculated in a thick enough film, L z > L z,max , with a sufficiently large surface anisotropy constant. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4979864\]
Role of interfaces in higher order angular terms of magnetic anisotropies: ultrathin film structures
Journal of Magnetism and Magnetic Materials, 2001
The role of interface inhomogeneities on macroscopic magnetic anisotropy terms was investigated using simple mathematical modeling. It is shown that the intrinsic anisotropies caused by the spin-orbit interaction in the presence of lateral inhomogeneities can create additional magnetic anisotropies with higher order angular terms. The lateral inhomogeneous distribution of the uniaxial anisotropy can result in the presence of a fourth order angular term. These anisotropies decrease the total energy, and their strength is affected by the exchange averaging effect. Large atomic terraces allow the local magnetic moment to deviate from the mean orientation resulting in negative higher order angular terms in magnetic anisotropies satisfying the sample symmetry. The negative sign results in the magnetic easy axes being oriented 451 with respect to the intrinsic uniaxial axis. It is shown that the additional higher order terms do not always have to satisfy the time inversion symmetry. Odd powers in directional cosines can arise when the exchange restoring torque becomes comparable to or weaker than torques from the internal fields. The additional higher order angular terms in magnetic anisotropies decrease usually more rapidly with the sample thickness than the intrinsic interface anisotropies. Their rapid decrease in strength with an increasing sample thickness allows one to distinguish them from the intrinsic interface anisotropies. It will be shown that the magnetic anisotropies originating in interface inhomogeneities can play an important role in the magnetic phase transitions of ultrathin film structures. r
Journal of Magnetism and Magnetic Materials, 2012
Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of ultrathin Co9Ni multilayer films with a thin permalloy layer underneath. MTXM images with a spatial resolution better than 25 nm were obtained at the Co L 3 edge down to an equivalent thickness of Co of only 1 nm, which establishes a new lower boundary on the sensitivity limit of MTXM. Domain sizes are shown to be strong functions of the anisotropy and thickness of the film.
Effect of submonolayer coverage of Fe and Mn films on the magnetization direction of
Journal of Magnetism and Magnetic Materials, 2004
Ni=Cuð1 0 0Þ films are known to exhibit an ''inverse'' reorientation transition at 8-10 ML: In contrast to Fe or Co ultrathin films one observes that the magnetization rotates from in-plane to out-of-plane upon increasing the thickness. The driving force for this phenomenon is the tetragonal distortion of the film which results in a volume uniaxial anisotropy, which favors an out-of-plane orientation of the magnetization. The effect of submonolayer coverage of Fe and Mn on Ni reorientation transition is studied by means of Magneto-Optic Kerr effect (MOKE). Fe overlayers are found to have a marked influence on the interface anisotropy of Ni films resulting in a strong reduction of the critical thickness. In the submonolayer regime, interface anisotropy favors out-of-plane magnetization. Extrapolation to the fully formed interface shows a negative anisotropy. Mn overlayers did not have any dramatic effect on the SRT thickness. Hence do not change significantly the surface anisotropy. r
Influence of film morphology on perpendicular magnetic anisotropy
Physical Review B, 2001
Perpendicular magnetic anisotropy ͑PMA͒ appears in epitaxial films mainly due to the broken symmetry at the interface. As a result, ultrathin magnetic layers tend to be perpendicularly magnetized. With increasing film thickness, the shape anisotropy overcomes this interface contribution and forces the sample magnetization into the surface plane. We show that previous experimental studies of the magnetic anisotropy energies in the Co/Cu͑111͒ system are affected by the large roughness of the Co films, resulting in underestimated values for the Co-Cu interface anisotropy. By using a surfactant ͑Pb͒ to assist the growth of Co layers we are able to prepare Co films and Cu/Co bilayers of homogeneous thickness and negligible roughness, and to determine a more accurate value for the Co-Cu interface anisotropy. With the aid of a simple model calculation, we demonstrate that roughness will substantially affect experimentally determined values of PMA.
Magnetic thin films and multilayers
Applied Surface Science, 1994
New surprising magnetic phenomena occur in artificial metallic thin films and multilayers. In this paper wc briefly discuss the competition between spin-orbit coupling and dipolar interactions which may favour the alignment of electron spins in directions either perpendicular or parallel to the interfaces. Moreover, we review shortly thc oscillations in the exchange coupling between magnetic layers separated by paramagnetic spacers as a function of thc thickness of the latter and the associated phenomenon of the giant magneto-resistance. 0169-4332/94/$(17.00
Competing magnetic interactions in exchange-bias-modulated films
Physical Review B, 2010
The magnetization reversal in stripe-like exchange bias patterned Ni81Fe19/IrMn thin films was investigated by complementary inductive and high resolution magneto optical magnetometry, magneto optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange bias direction. Due to the interaction of interfacial coupling, exchange, and magneto-static energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micro-patterned exchange bias films.
Field effects on the magnetic properties of three-layer films
Physica B-condensed Matter, 2003
We study by extensive Monte Carlo (MC) simulations and Green function (GF) method some properties of a system composed of three thin ferromagnetic (FM) films coupled to each other by an antiferromagnetic (AF) interface exchange interaction in the presence of a magnetic field H perpendicular to the film surfaces. The films have a triangular lattice structure with Ising spins. In the simplest case, where all interactions except the interface ones are FM and taken to be equal to J ¼ 1; and the interface interactions between the second (middle) film and its neighboring first and third films, J 12 and J 23 ; are equal to À1; the ðT; HÞ-phase diagram obtained by MC simulations shows several interesting features. While for H smaller than the critical value H t there observed a second-order phase transition at a finite T from the AF ordering to paramagnetic phase, for H > H t the transition becomes of first-order. The field H t depends on the interface interactions and the film thickness. The hysteresis cycle measured in the transition region by field-heating and field-cooling shows a two-step cycle which may have important practical applications in magnetic recording. An analytical calculation by the GF method using an Ising-like model has been performed for the same system. The obtained self-consistent layer magnetizations are in excellent agreement with the MC ones.
Hysteresis loops of magnetic thin films with perpendicular anisotropy
Phys Rev B, 2005
We model the magnetization of quasi-two-dimensional systems with easy perpendicular (z) axis anisotropy upon change of the external magnetic field along z . The model is a generalization of the scalar “phi-fourth” model that considers only the z component of the magnetization, and includes magnetic exchange, dipolar interactions, structural disorder, and an external z -oriented magnetic field. The phase diagram in the disorder/interaction strength plane is presented, and the different qualitative regimes are analyzed, mainly focusing on the existence or not of an abrupt nucleation step in the process of magnetization reversal. The results compare very well with observed experimental hysteresis loops and spatial magnetization patterns, as for instance in the case of Co-Pt multilayers.