Mechanism Of Magnetic Anisotropy Research Articles

Uniaxial in-plane magnetic anisotropy mechanism in Ni, Fe, and Ni-Fe alloy films deposited on single crystal Y-cut 128° LiNbO3 using magnetron sputtering

We investigated the mechanism of induced in-plane uniaxial magnetic anisotropy (Ku) in Nickel (Ni), Iron (Fe), and Ni-Fe alloy films deposited in situ on a single-crystal 128° Y-cut LiNbO3 (LNO) substrate at various substrate heating temperatures (Th) in the range 30–400 °C through radio frequency magnetron sputtering or co-sputtering. The results show that the Ku values for the Ni, Fe, and Ni-Fe alloy films are induced in the (01.2) or (21¯.0) planes of the LNO substrate. The highest value of Ku for the Ni films was observed at Th = 200 °C, which is owing to the increased orientation of the fcc Ni (311) plane. The Ni film with thickness t ∼ 20 nm deposited on the LNO substrate at Th = 200 °C possesses the highest value of Ku. Density functional theory calculations show that the magnetic anisotropic energy on the fcc Ni (311) plane differs depending on the magnetization direction in the in-plane direction in the model. Meanwhile, the value of Ku for the Fe films decreases with an increase in the value of Th because the films with higher Th are polycrystalline and have an oxide layer. The composition dependence of Ku for Ni-Fe alloy films at Th = 30 °C shows a trend similar to the crystal magnetic anisotropy for bulk Ni-Fe alloy. The induced Ku on LNO is attributed to the magnetostriction effect with the change in the crystal orientation of the ferromagnetic metal owing to a strain from the LNO substrate through the thermal expansion during sputtering. These results indicate the origin of the induced Ku in the Ni and Fe based metallic material films deposited on the LNO substrate.

Toward two-dimensional ionic crystals with intrinsic ferromagnetism

Modern advanced technologies have been employed to synthesize new two-dimensional (2D) materials of various compositions. Since ionic bonds have no orientation, the ability of 2D ionic crystals to resist thermal fluctuation perpendicular to the 2D surface is worth studying. In this paper, we propose a theoretical analysis on the existence of 2D ionic EuS crystals. Although the Mermin-Wagner theorem denies the possibility of long-range magnetic order in 2D systems, our theoretical model predicts that 2D EuS crystals are ferromagnetic semiconductors. The mechanism of magnetic anisotropy in maintaining the magnetic order is uncovered. The model indicates the effect of the low-energy gap in the spin-wave spectrum on preventing thermal disturbance from destroying the ferromagnetism. A new type of magnetic interaction in 2D EuS crystals is revealed, which leads to the enhancement of Curie temperature by applying a gate voltage. Our theoretical research can benefit future research of other magnetic 2D crystals.

Magnetic ground state of the ordered double-perovskite Sr2YbRuO6 : Two magnetic transitions

Comprehensive muon spin rotation/relaxation (muSR) and neutron powder diffraction (NPD) studies supported via bulk measurements have been performed on the ordered double perovskite Sr2YbRuO6 to investigate the nature of the magnetic ground state. Two sharp transitions at TN1 ~ 42 K and TN2 ~ 36 K have been observed in the static and dynamic magnetization measurements, coinciding with the heat capacity data. In order to confirm the origin of the observed phase transitions and the magnetic ground state, microscopic evidences are presented here. An initial indication of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate near TN1. NPD confirms that the magnetic ground state of Sr2YbRuO6 consists of an antiferromagnetic (AFM) structure with interpenetrating lattices of parallel Yb3+ and Ru5+ moments lying in the ab-plane and adopting a A-type AFM structure. Intriguingly, a small but remarkable change is observed in the long-range ordering parameters at TN2 confirming the presence of a weak spin reorientation (i.e. change in spin configuration) transition of Ru and Yb moments, as well as a change in the magnetic moment evolution of the Yb3+ spins at TN2. The temperature dependent behaviour of the Yb3+ and Ru5+ moments suggests that the 4d-electrons of Ru5+ play a dominating role in stabilizing the long range ordered magnetic ground state in the double perovskite Sr2YbRuO6 whereas only the Yb3+ moments show an arrest at TN2. The observed magnetic structure and the presence of a ferromagnetic interaction between Ru- and Yb- ions are explained with use of the Goodenough-Kanamori-Anderson (GKA) rules. Possible reasons for the presence of the second magnetic phase transition and of a compensation point in the magnetization data are linked to competing mechanisms of magnetic anisotropy.

Solar Faculae: Microturbulence as an Indicator of Inclined Magnetic Fields

The observations of the solar facula in the Ba II λ 455.403 A line are used to construct a 3D model of the facula area by solving the inverse nonequilibrium radiative transfer problem and to investigate the fine structure of the field of unresolved velocities (microturbulence). New turbulent structures are formed in the layers of the upper photosphere. They are localized mainly between upward and downward flows with the formation of ring-shaped structures of increased turbulence around these flows. The mechanism of magnetic anisotropy of microturbulent velocity is proposed (small-scale eddy-type plasma motions mainly occur in the planes perpendicular to the magnetic field), which explains the height dependence of the field of unresolved velocities. Anisotropy of microturbulence begins to manifest itself in the lower photospheric layers outside the upward and downward flows, while it manifests itself in the higher layers inside these flows. The increase of microturbulence in the layers of the upper photosphere and the lower chromosphere in the areas between matter flows indicates the presence of inclined magnetic fields, which, along with the blurring of its spatial structure, indicates the existence of a magnetic canopy region. Microturbulence can be used as an additional tool for diagnostics of inclined magnetic fields.

Magnetic and structural properties of L1-Mn50Ga50-xAlx epitaxially grown thin films

Epitaxially grown L10- MnGa(Al) continuous thin films with the c-axis along the film normal are successfully fabricated on MgO (001) substrates at a substrate deposition temperature Ts of around 400 °C. The order parameter S is found to decrease with Al content, except for that for Al = 0. The films under consideration exhibit the perpendicular magnetic anisotropy constant Ku of about 1 x 107 erg/cm3 at 300 K. In order to clarify the magnetic anisotropy mechanism, the correlation between Ms(T) and Ku(T) is discussed. It is found that the values of n in the power law relation Ku(T) ∼ Ms(T)n are found to be 2.6, 2.3, and 2.0 for the films of 2.5, 5.6, 11.2 Al at%, respectively. The present result suggests that the magnetic anisotropy of L10-MnGaAl thin films may be explained in terms of the two-ion model, where both the contributions of Mn and Ga are significant to the total magnetic anisotropy”. The decrease of the value n with Al addition n is of interest, but the reason for this change is not understood at present.

Understanding High Anisotropic Magnetism by Ultrathin Shell Layer Formation for Magnetically Hard–Soft Core–Shell Nanostructures

Magnetic core–shell nanostructures offer a viable solution for tunable magnetism via nanoscale exchange interactions in a single-component unit. A typical synthetic approach for monodisperse bimagnetic ferrite core–shell nanostructures employs the seed-mediated growth method using the heating-up process. Understanding magnetic core–shell interface formation and their interactions is crucial; however, the magnetical persistence of the pristine core component during the heating-up process is unclear. Here, we elucidate the enhancement mechanism of magnetic anisotropy when the hard–soft core–shell nanostructures are formed with the ultrathin shell layer. The heating-up effect on the core component exhibits the coordination change of ligand chemisorption with surface metal ions, which leads to a substantial increase in surface anisotropy due to enhanced spin–orbit couplings. We further demonstrate that the selection of metal precursors and surfactants for additional shell layer formation is important. The kin...

Magnetic and Structural Properties of L10 Mn–Ga–Al Epitaxially Grown Thin Films of Island Structure

Magnetic and Structural Properties of L1₀ Mn–Ga–Al Epitaxially Grown Thin Films of Island Structure

Magnetic and structural properties of L10 Mn-Ga epitaxially grown islands

Magnetic and structural properties of L10 Mn53Ga47 islands epitaxially grown onto MgO(1 0 0) substrates are discussed. The samples were fabricated by sputter-deposition at a substrate temperature Ts during deposition. The samples deposited at Ts above 500 °C were found to form the island structure of Volmer-Weber type. The average size of the islands fabricated at Ts = 600 °C is around 200 nm in width and 60 nm in height. The XRD and TEM analyses indicate that those islands are of the L10 phase with the 〈0 0 1〉 axis perpendicular to the substrate surface. The lattice constants a and c are 3.91 ± 0.01 Å and 3.65 ± 0.02 Å, respectively, which are larger by 0.8%, and smaller by 1.5% respectively, as compared to the bulk values of the same composition. The order parameter of these islands is found to increase from 0.7 to 0.8 for Ts = 450–500 °C, and then remains nearly constant (≈0.8) for higher Ts. The M-H hysteresis loops exhibit a high squareness for all the samples for Ts = 450–600 °C. The saturation magnetization Ms is about 220 and 350 emu/cm3 for Ts = 450 and 600 °C, respectively. The out-of-plane coercivity Hc is 5 and 13 kOe for Ts = 450 and 600 °C, respectively. The temperature dependence of Ms for the sample made at Ts = 600 °C was measured and fitted to an empirical relation in order to estimate Tc. The estimated Tc around 600 K is in reasonable agreement with the reported value of bulk L10 Mn53Ga47. The uniaxial perpendicular magnetic anisotropy constant Ku estimated by the out-of-plane torque curves is around 1.1 × 107 and 8.3 × 106 erg/cm3 at 5 and 300 K, respectively. The initial magnetization curves of these islands exhibit a typical pinning mode for the coercivity mechanism. A phenomenological discussion of the coercivity is presented on the basis of Kronmuller’s formula. It is found that the coefficient α and effective demagnetizing factor Neff in the formula by Kronmuller are approximately 0.38 and 12. For the magnetic anisotropy mechanism, the power law relation between Ku(T) and Ms(T) is examined. It is found that the exponent n for Ku(T)∝Ms(T)n varies from 2.3 to 3.5 for T from 350 to 5 K. However, the n in a whole temperature range from 5 to 350 K is 2.6. The n = 2.6 suggests a deviation from the single-ion mechanism, and is consistent with the theoretical predictions of Ga contribution.

Magnetic Anisotropy of $\tau $ -MnAl Thin Films

Manganese compounds such as MnAl, MnBi, MnGa have received much attention for their high magnetic anisotropy constants, and also for rare-earth free permanent magnet applications. Despite the fact that voluminous work has been conducted regarding the magnetic anisotropy, the origin of this high magnetic anisotropy energy is not well understood. In the case of MnAl, both Mn and Al elements are known to possess low spin-orbit coupling constants, but the τ-phase MnAl is well known to exhibit high magnetic anisotropy constant K in the order of 1×107 erg/cm3 at room temperature [1]. A systematic study of temperature dependence of both the saturation magnetization M S and magnetic anisotropy constant K in τ-MnAl thin films has been carried out in order to elucidate the magnetic anisotropy mechanism.

Magnetic anisotropy energy in disordered [formula omitted

We theoretically analyze the influence of chemical disorder on magnetic anisotropy in Ge1−xMnxTe semiconductor layers known to exhibit carrier-induced ferromagnetism and ferroelectric distortion of rhombohedral crystal lattice. Using DFT method we determine the local changes in the crystal structure due to Mn ions substitution for Ge and due to the presence in Ge1−xMnxTe of very high concentration of cation vacancies. We calculate the effect of this structural and chemical disorder on single ion magnetic anisotropy mechanism and show that its contribution is of the order of magnitude smaller as compared to magnetic anisotropy mechanism originating from the spin polarization induced by Mn ions into neighboring Te and Ge ions. We also discuss magnetic anisotropy effects due to pairs of Mn ions differently allocated in the lattice. The spatial averaging over chemical disorder strongly reduces the strength of this magnetic anisotropy mechanism and restores the global rhombohedral symmetry of magnetic system.

DFT calculations of magnetic anisotropy energy of Ge1−xMnxTe ferromagnetic semiconductor

Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge1−xMnxTe were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin–orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge1−xMnxTe (1 1 1) thin layers.

Effect of strain on the magnetic anisotropy in the epitaxial magnetic thin films

A phenomenological thermodynamic theory of magnetic thin films epitaxially grown on cubic substrates is developed by considering the thermodynamic potential, which corresponds to the actual mechanical boundary conditions. For clamped magnetic thin films with two-dimension strains, the study reveals that the magnitudes of remanent magnetization M r and coercive field H c are dependent on the strain induced by the lattice mismatch. The tensile strain can significantly enhance the out-of-plane magnetization with a larger coercivity, while the compressive strain makes correspondingly thin films exhibit an opposite in-plane magnetic anisotropy. Our analysis provides a profound understanding of magnetic anisotropy mechanism and the relationship with lattice strain in the epitaxial magnetic thin film.

A study of the induced magnetic anisotropy mechanism in acicular cobalt-ferrite particles

The influence of Fe2+ ions on the coercivity and induced magnetic anisotropy of acicular cobalt-ferrite particles was studied. When the Co2+ content was constant, the coercivity and induced magnetic anisotropy linearly increased with increasing Fe2+ content of the acicular cobalt-ferrite particles. The activation energy E of these samples was measured and found to be about 0.4 eV. A model of Co2+ and Fe2+ pairs oriented along the magnetic field direction to induce a uniaxial magnetic anisotropy after magnetic annealing is proposed to explain the experimental results.

MBE growth and magneto-optic properties of magnetic multilayers

Recent interest in the magnetic and magneto-optic properties of transition metal/transition metal multilayers has been stimulated by the discovery of perpendicular magnetism in particular systems such as Co/Pd and Co/Pt. Due to their favorable magneto-optic wavelength dependence and enhanced corrosion resistance, these materials show promise as future data storage media. However, partially due to the large variety of thin-film deposition methods and growth conditions, it has been difficult to obtain a clear understanding of the mechanisms of magnetic anisotropy in these systems. In order to create controlled and well characterized model systems, we have grown a series of epitaxial Co/Pd superlattices oriented along the three high-symmetry crystal directions [001], [110], and [111] on single-crystal GaAs substrates by molecular beam epitaxy [MBE]. Simultaneously, we have deposited polycrystalline Co/Pd multilayers on Si substrates mounted alongside the GaAs for direct comparisons of epitaxial and non-epitaxial films produced under identical conditions. The structural properties of these multilayers were determined by low-and reflection high-energy electron diffraction (LEED and RHEED), low- and high-angle X-ray diffraction, and scanning tunneling microscopy (STM). The dependence of the uniaxial magnetic anisotropy energy on the Co thickness in these superlattices showed significant systematic differences for each of the three crystal orientations. A review of our work on the structural influences responsible for these differences is presented.

Magnetic and magneto-optical properties of (Nd,Pr)-(Fe,Co) alloy amorphous films with huge perpendicular magnetic anisotropy

An extensive study of the magnetic and magneto-optical properties for Nd x Fe 100-x , Pr x Fe 100-x and Nd 40 - Fe 51 Co 6 Ti 3 amorphous films synthesized by r.f. sputtering onto heated substrates has been carried out. Both Nd-Fe and Pr-Fe alloy films exhibit the maximum values of the perpendicular magnetic anisotropy constant K u at 300K at about 40 at% of Nd and Pr elements. The strong thickness dependence of K u was found in both Nd 40 Fe 51 - Co 6 Ti 3 and Pr 40 Fe 60 films fabricated at the substrate deposition temperature T_{s}=210 \sim 250\deg C. The Kerr rotation angle θ K increases with decreasing wavelength in the range from 350 to 800 nm in those alloy films with Nd and Pr. This trend is in contrast to that of films with heavy rare earths. Together with observation by high resolution electron microscopy, it is proposed that a short range atomic ordering in a microcrystalline amorphous structure plays an important role in the perpendicular magnetic anisotropy mechanism.

Structure, magnetization reversal, and magnetic anisotropy of evaporated cobalt films with high coercivity

Grain structure, crystal structure, and magnetic properties relating to coercivity of cobalt thin films with high coercivity are described. Cobalt films evaporated under vacuum at a normal angle of incidence on thallium and titanium sublayers and at a high angle of incidence on a substrate have a coercivity higher than 400 Oe. Transmission electron microscopy shows that the grain structure of the film deposited on a thallium sublayer is like large islands and that the grain structure of the film deposited at a high angle of incidence is columnar. The grain structure of the film deposited on a titanium sublayer, when similarly examined, seems homogeneous. Magnetization reversal and the magnetic anisotropy mechanism under whose influence magnetization is reversed have been investigated using the rotational hysteresis measurement method. A noncoherent rotation process is operative in these films in spite of the differences in the grain and crystal structures and the coercivity. The magnetic anisotropy for the film on the titanium sublayer is probably the magnetocrystalline anistropy of cobalt. On the other hand, the columnar grain shape anistropy should be added to the magnetocrystalline anistropy of cobalt in the oblique incidence film.

A new mechanism of magnetic anisotropy due to π-f exchange in graphite intercalation compound C 6Eu

The origin of XY magnetic anisotropy observed in antiferromagnet C 6Eu is studied theoretically. A new mechanism of magnetic anisotropy due to the combined action of the π-f exchange and the spin-orbit interaction is proposed. It is shown that this mechanism overcomes the ordinary mechanism due to the crystal field in the case of a Eu 2+ ion.