Thickness dependence of magnetization structures in thin Permalloy rectangles (original) (raw)
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Micromagnetic Modelling of Hysteresis in Permalloy Thin Films with Non-Magnetic Defects
HAL (Le Centre pour la Communication Scientifique Directe), 2022
In this paper, we present the results of numerical micromagnetic modelling of the domain wall pinning on nonmagnetic defects in a ferromagnetic thin sheet of permalloy. We compared the influence of different distribution of nonmagnetic inclusions on the magnetization reversal in case of uniaxial anisotropy. It is shown that the non-magnetic defects help to resolve vortex singularities and play a role of pinning states. It is demonstrated that the defects located on the sides of the sheet favor the transition into the single-domain state. By varying the in-plane anisotropy constant, we observed that the defects located in the center lead to higher coercivity, when the domain wall width is comparable to the size of the sample, but narrowing of domain wall width leads to a change of energetically favorable distribution of defects and the highest is when defects are located on the sides. It is shown that the defects located in the corner of the sheet serve as nucleation points for the magnetization reversal process and have a lower threshold for unpinning of the domain walls.
Finite size effects in patterned magnetic permalloy films
Journal of Applied Physics, 2000
Electron beam lithography has been used to prepare 250-Å-thick square-shaped permalloy dots whose width and separation are in the range between 1 and 4 m. The static and dynamic magnetic properties of these structures have been investigated by complementary techniques such as magneto-optic Kerr effect ͑MOKE͒, magnetic force microscopy ͑MFM͒, and Brillouin light scattering ͑BLS͒. Longitudinal MOKE enabled us to compare the hysteresis loops of the specimens with different dot size and interdot separation, showing a marked influence of the demagnetizing field inside the dots. MFM images recorded at zero applied field showed that, depending on the interdot spacing, there is a prevalence of either four-or seven-domain patterns together with a minority of nonsolenoidal patterns that possess a net magnetic moment. BLS from thermally activated spin waves were then used to determine the intrinsic magnetic parameters of the permalloy films and to show evidence of the discretization of the spin-wave peak due to the wave vector resonance condition within each dot.
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\]
Magnetic energies of single submicron permalloy rectangles determined via magnetotransport
Physical Review B, 2009
We have investigated the magnetic properties of single submicron permalloy rectangles with a thickness of 20 nm and an aspect ratio of 2:1 via anisotropic magnetoresistance ͑AMR͒. Preparation and investigation via magnetotransport are performed in situ in ultrahigh vacuum. The field-dependent magnetization behavior of the two generic cases with the magnetic field applied perpendicular and parallel to the long axis of the rectangles is studied. Due to the high sensitivity of our setup, single field sweeps are sufficient to obtain magnetoresistance curves of structures with dimensions as small as 600ϫ 300 nm 2 . To link features of the AMR to changes in the micromagnetic states, the remanent state has been investigated via scanning electron microscopy with polarization analysis. Our main result is that the energy density of micromagnetic states can be obtained from the hard-axis magnetization behavior. It is demonstrated that a C/S state can be distinguished from a Landau state and the energy difference between both states is determined.
Micromagnetics of laminated Permalloy films
IEEE Transactions on Magnetics, 1988
A single-layer Permalloy strip with a transverse magnetic easy axis generally has 90" closure domains and associated Bloch walls. However, for certain applications, transversely magnetized single-domain states may be preferred. Laminating the Permalloy by alternating magnetic and nonmagnetic sublayers can eliminate closure domains by permitting flux closure through the nonmagnetic spacers along the edges of the strip. A new kind of 90" wall lying along the edge describes the region where flux closure takes place. The profile and energy of this edge curling wall (ECW) follow from micromagnetic principles. The ECW is observed in an optical Kerr microscope. Conditions are derived energetically favoring single transverse domains with ECW's over either multiple closure domains or single longitudinal domains that are undesirable because of their low permeability. Computed figures illustrate how the maximum permissible spacer thickness depends on Permalloy sublayer thickness, uniaxial anisotropy, width of the magnetic strip, mismatch of Permalloy thickness, and perpendicular anisotropy. The case with strip width W = 100 wm and vanishing magnetostriction or stress should require only a few sublayers. However, if W is very small, or if stress-induced or some other form of perpendicular anisotropy is excessive, then attainment of single transversely magnetized domains requires many sublayers. Some of these conclusions are supported by microscopic observations.
Physica B, 2000
A micromagnetic study of non-magnetic periodic structures in magnetic thin "lms has been carried out. Periodic arrays of non-magnetic squares and rectangles are pointed out as the most appropriate systems for engineering hysteresis properties and ultra-high density storage applications. Non-magnetic structures with size ranging from 2l to 10l have been studied, l being the exchange length of the magnetic material. Variations in the coercivity of two orders of magnitude are found for some rectangle arrays depending on the direction of the applied "eld. Remanent states adequate for magnetic storage in rectangular bits for a theoretical alloy with l / "0.5 ( ,wall width parameter) have been found to record areal densities in the order of 750 Gbits/in.
Micromagnetism of two-dimensional permalloy particles with different aspect ratios
Applied Physics A: Materials Science & Processing, 2003
ABSTRACT Micromagnetic properties of the Fe19Ni81 (5nm)/NiO (50nm)/Fe19Ni81 (30nm) structured system have been investigated in a photoemission electron microscope in the magnetic X-ray circular dichroism operating mode. The microstructured Fe19Ni81 (5nm) film contained two-dimensional islands with the aspect ratio varying from 1:1 to 10:1, and the linear size of their long axis comprised 24, 12 and 6μm. It is shown that the magnetic domains have the direction of magnetization preferentially parallel and antiparallel to the magnetic field direction in which this system was prepared. Their number is determined by the particles’ sizes, their shape as well as by the direction of the external magnetizing field and can be characterized by a non-monotonic size dependence. The magnetization of domains with different lateral sizes was found to be 0.4T with an accuracy better than 20%.
Structure and Magnetic Properties of Thin Permalloy Films Near the “Transcritical” State
IEEE Transactions on Magnetics, 2010
Various series of permalloy thin films were grown by dc-sputtering on Si (100) and glass substrates at room temperature and different argon pressure values using a Fe 20 Ni 80 target. The increase of argon pressure leads to a decrease of the Fe concentration in the films from 17 at.% to 15 at.%, an increase of the root mean square roughness of film surfaces, and a decrease of the sharpness of the crystalline texture of the samples. The increase of the film thickness leads to an increase of the coercive field. The transition to the "transcritical" state was observed at a critical thickness that decreases from 220 to 50 nm as the argon pressure in the chamber increases. This state was confirmed by the characteristic shapes of hysteresis loops, rotatable magnetic anisotropy, and the appearance of stripe domains.
Journal of Nanoscience and Nanotechnology, 2011
Magnetization dynamics and field dependent magnetization of different devices based on 25-30 nm thick Permalloy (Py) films: such as single Py layers (Py/MgO; Py/CoFeB/Al 2 O 3 and Py inserted as a magnetic layer in magnetic tunnel junctions (Py/CoFe/Al 2 O 3 /CoFe; Py/CoFeB/Al 2 O 3 /CoFe; Py/MgO/Fe) have been extensively studied within a temperature range between 300 K down to 2 K. The dynamic response was investigated in the linear regime measuring the ferromagnetic resonance response of the Py layers using broadband vector network analyzer technique. Both the static and the dynamic properties suggest the possible presence of a thermally induced spin reorientation transition in the Py interface at temperatures around 60 K in the all samples investigated. It seems, however, that the details of the interface between Py and the hardening ferromagnet/insulator structure, the atomic structure of Py layers (amorphous vs. textured) as well as the presence of dipolar coupling through the insulating barrier in the magnetic tunnel junction structures could strongly influence this low temperature reorientation transition. Our conclusions are indirectly supported by structural characterization of the samples by means of X-Ray diffraction and high resolution transmission electron microscopy techniques. Micromagnetic simulations indicate the possibility of strongly enhanced surface anisotropy in thin Py films over CoFe or CoFeB underlayers. Comparison of the simulations with experimental results also shows that the thermally-induced spin reorientation transition could be influenced by the presence of strong disorder at the surface.
The effect of the in-plane demagnetizing field on films with weak perpendicular magnetic anisotropy
2006
The effect of reduced lateral dimension on the magnetic behavior of long microstrips with weak perpendicular magnetic anisotropy has been studied. The hysteresis loops of the surface and the whole volume of microstrips and large films have been recorded by magneto-optic Kerr effect magnetometry and vibrating sample magnetometry. Also, the magnetic structure of the microstrips and its evolution under an applied field have been studied by magnetic force microscopy and the Bitter technique. It has been observed that the transversal dimension of the microstrips gives rise mainly to an in-plane demagnetizing field which affects their hysteresis loops and magnetic structure in a different manner. A great increase in the surface coercivity in the transversal direction of the microstrips is the main unexpected effect that has been observed. On the other hand, the magnetic structure in remanence and its evolution with increasing thickness have not revealed a significant dependence on the direction of the last saturating field. It has also been observed that the reduced size of the microstrips in their transversal direction does not prevent the occurrence of the property known as rotatable anisotropy, typical of films with stripe domain structure, although it makes this property very anisotropic. Finally, a two-dimensional qualitative model of closed flux stripe domain structure has been used for correlating the enlargement of the surface coercivity of the microstrips with the evolution of their magnetic structure.