Soft Permalloy Research Articles

High Curie temperature and high magnetization potential Fe2CoS alloy soft magnet

Developing soft magnets is attracting extensive research efforts for several device applications and other issues. Here, we investigate the finite temperature magnetic properties of the Fe2CoS alloy using first-principles density functional theory calculations and Monte Carlo simulations. Without a demagnetization factor, it exhibits semi-hard-magnetic properties at room temperature. For instance, it exhibits a coercivity of 290 mT, a magnetic anisotropy constant of 218 kJ/m3, and a magnetic hardness parameter of 0.3. By considering the demagnetization factor at 300 K, the coercivity, magnetic anisotropy constant, and hardness parameter are reduced to 1.5 mT, 0.7 kJ/m3, and 0.035. Besides, compared to ferrites soft magnets, the Fe2CoS alloy shows a high relative permeability of 10,000 and low energy loss of 0.16 Watt/kg. The curie temperature (940 K) and high saturation magnetization MS (1.49 T) of the Fe2CoS alloy are significantly higher than those of soft ferrites and Permalloy. Therefore, we propose that the Fe2CoS alloy can be used as a potential Fe-based soft magnet.

Mapping AC susceptibility with quantum diamond microscope

We present a technique for determining the micro-scale AC susceptibility of magnetic materials. We use the magnetic field sensing properties of nitrogen-vacancy (NV-) centers in diamond to gather quantitative data about the magnetic state of the magnetic material under investigation. A quantum diamond microscope with an integrated lock-in camera is used to perform pixel-by-pixel, lock-in detection of NV- photo-luminescence for high-speed magnetic field imaging. In addition, a secondary sensor is employed to isolate the effect of the excitation field from fields arising from magnetic structures on NV- centers. We demonstrate our experimental technique by measuring the AC susceptibility of soft permalloy micro-magnets at excitation frequencies of up to 20Hz with a spatial resolution of 1.2 µm and a field of view of 100 µm. Our work paves the way for microscopic measurement of AC susceptibilities of magnetic materials relevant to physical, biological, and material sciences.

Magnetization reversal and ground states in thin truncated conical nanodisks: Analytical and micromagnetic modelling approach

Simulation of magnetization reversal of soft permalloy thin truncated conical disks is done using micromagnetic modelling. The thickness of the disks are fixed at 20nm. Base radius (R) of the conical disk is varied between 50−100nm while the radius of upper surface (r) is varied such that the ratio σ=r/R lies between 0 to 1. As the conical disks are gradually tapered by reducing r, the remanent states change from vortex state to shifted vortex state to buckled magnetization state. In buckled state, the magnetic moments are essentially parallel except at the corners where they curl away from the applied field direction. The extent of curling away of magnetization in buckled state reduce as base radius R is decreased. Thus at smaller base radius, the buckled states converge to homogeneous magnetization state or so called ferromagnetic state. Analytical expressions for the total energy of these three remanent states are calculated using simple models. Analytical calculations reveal that vortex configuration is the ground state for a wide range of geometrical parameters and shifted vortex state is a metastable state which appears as remanent state in the in-plane magnetization reversal due to a possible existence of energy barrier. Other observations from micromagnetic simulations are well corroborated by the results of analytical calculations.

Enhancement the perpendicular magnetic anisotropy of nanopatterned hard/soft bilayer magnetic antidot arrays for spintronic application

Development of perpendicular magnetic anisotropy thin films is a requisite for many applications. In this work, we have illustrated the enhancement of the PMA of Hard (Co)/Soft (Permalloy, Py) ferromagnetic bilayers by depositing them onto nanoporous anodic alumina membranes with different hole diameters varying in the range between 30 nm and 95 nm. A dramatic change in the hysteresis loops behaviour with hole size, D, and magnetic surface cover ratio parameters has been observed: (1) for samples with small antidot hole diameters, the in-plane (INP) hysteresis loops show single-step magnetic behaviour; (2) for D = 75 nm, the hysteresis loops of Co/Py and Py samples exhibit a multistep magnetic behaviour; (3) a decreasing coercivity in the INP hysteresis loops for antidot arrays samples with D> 75 nm has been detected as a consequence of the reduction of the INP magnetic anisotropy and the rising of the out-of-plane component. A crossover of the magnetic anisotropy from the INP to out-of-plane for bilayer antidot samples has been observed for Co/Py ferromagnetic bilayers, favoured by the interfacial exchange coupling between the two ferromagnetic materials. These findings can be of high interest for the development of novel magnetic sensors and for perpendicular-magnetic recording patterned media based on template-assisted deposition techniques.

Nanopatterned hard/soft bilayer magnetic antidot arrays with long-range periodicity

A top-down approach using focused ion beam has been employed to fabricate Co/Permalloy hard-soft bilayer magnetic antidot arrays. These nanopatterned films are studied with particular emphasis on magnetic coercivity. The antidots have a diameter of 40 nm and the studied antidot symmetries are square and hexagonal. A dependence of magnetic coercivity on the relative thicknesses of the magnetically hard (Co) and soft (Permalloy) layers is found; increasing Permalloy thickness results in lower magnetic coercivity. Furthermore, the long-range periodicity of top-down nanopatterned antidots results in higher magnetic coercivity and a stronger magnetic domain-wall pinning, compared to identical hard/soft bilayers of short-range order deposited on porous anodic alumina. The combination of antidot symmetry and hard/soft thickness, allow for efficient tailoring of the magnetic properties of nanopatterned thin films. Finally, magnetic force microscopy imaging of the antidot array magnetic configuration shows striking qualitative differences between the two array symmetries: square symmetry arrays have inhomogeneous magnetic state and a high density of immobile super-domain walls, whereas hexagonal symmetry arrays show a homogeneous magnetic configuration.

Magnetically induced anisotropy of flux penetration into strong-pinning superconductor/ferromagnet bilayers

We studied the impact of soft ferromagnetic permalloy (Py) on the shielding currents in a strong-pinning superconductor—YBa2Cu3O7−δ with Ba2Y(Nb/Ta)O6 nano-precipitates—by means of scanning transmission x-ray microscopy. Typically and in particular when in the thin film limit, superconductor/ferromagnet (SC/FM) bilayers exhibit isotropic properties of the flux line ensemble at all temperatures. However, in elements with small aspect ratio a significant anisotropy in flux penetration is observed. We explain this effect by local in-plane fields arising from anisotropic magnetic stray fields originated by the ferromagnet. This leads to direction-dependent motion of magnetic vortices inside the SC/FM bilayer. Our results demonstrate that small variations of the magnetic properties can have huge impact on the superconductor.

The magnetic reversal characteristics of 32-bit composite element magnetic barcodes

Magnetic barcodes containing 32 composite element bits have been produced and measured in order to optimize the design of magnetic microcarriers. Focused magneto-optic Kerr effect measurements allow the determination of the change in magnetic hysteresis when the width of magnetic elements is varied between bits, and the electron beam lithography used in production is confirmed to be accurate to ∼6 nm using scanning electron microscopy. The sharp magnetic switching observed, an important prerequisite for a functioning device, is attributed to the expected dipolar interactions between magnetic elements and the use of magnetically soft Permalloy. A crossover between two magnetic reversal behaviors is discovered when the magnetic elements are ∼200 nm wide. From these measurements, 12 bits were selected on which data can be written with a low probability of error, with the prospect of the other 20 bits being employed for error correction. We have therefore developed a nonvolatile magnetic memory on which 4096 unique codes can be programmed.

Overcoming the Limits of Vortex Formation in Magnetic Nanodots by Coupling to Antidot Matrix

Static magnetic configurations of thin circular soft (permalloy) magnetic nanodots, coupled to a hard antidot matrix with perpendicular magnetization, are studied by micromagnetic simulations. It is demonstrated, that dipolar fields of the antidot matrix promotes the formation of a magnetic vortex state in nanodots. The vortex is the dot ground state at zero external field in ultrathin nanodots with diameters as low as 60 nm, that is far beyond the vortex stability range in an isolated permalloy nanodot. Depending on the geometry and antidot matrix material it is possible to stabilize either radial vortex state or unconventional vortices with the angle between in-plane magnetization and radial direction ψ ≠ 0 , π / 2 .

Tunable magnetic vortex resonance in a potential well

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

Micromagnetic simulation study of magnetization reversal in torus-shaped permalloy nanorings

Using micromagnetic simulation, the magnetization reversal of soft permalloy rings of torus shape with major radius R varying within 20–100 nm has been investigated. The minor radius r of the torus rings was increased from 5 nm up to a maximum value r[Formula: see text] such that R- r[Formula: see text] = 10 nm. Micromagnetic simulation of in-plane hysteresis curve of these nanorings revealed that in the case of very thin rings (r [Formula: see text] 10 nm), the remanent state is found to be an onion state, whereas for all other rings, the remanent state is a vortex state. The area of the hysteresis loop was found to be decreasing gradually with the increment of r. The normalized area under the hysteresis loops (A[Formula: see text]) increases initially with increment of r. It attains a maximum for a certain value of r = r0 and again decreases thereafter. This value r0 increases as we decrease R and as a result, this peak feature is hardly visible in the case of smaller rings (rings having small R).

Development of flexible Ni80Fe20 magnetic nano-thin films

Flexible magnetic Ni80Fe20 thin films with excellent adhesion, mechanical and magnetic properties have been fabricated using magnetron plasma deposition. We demonstrate that flexible Ni80Fe20 thin films maintain their non-flexible magnetic properties when the films are over 60nm thick. However, when their thickness is reduced, the flexible thin films display significant increase in their magnetic coercive field compared to identical films coated on a solid Silicon substrate. For a 15nm flexible Ni80Fe20 film coated onto 110µm Polyvinylidene fluoride polymer substrate, we achieved a remarkable 355% increase in the magnetic coercive field relative to the same film deposited onto a Si substrate. Experimental evidence, backed by micro-magnetic modelling, indicates that the increase in the coercive fields is related to the larger roughness texture of the flexible substrates. This effect essentially transforms soft Ni80Fe20 permalloy thin films into medium/hard magnetic films allowing not only mechanical flexibility of the structure, but also fine tuning of their magnetic properties.

Magnetic domain-wall dynamics in wide permalloy strips

Domain walls in soft permalloy strips may exhibit various equilibrium micromagnetic structures depending on the width and thickness of the strip, ranging from the well-known transverse and vortex walls in narrow and thin strips to double and triple vortex walls recently reported in wider strips [V. Est\'evez and L. Laurson, Phys. Rev. B {\bf 91}, 054407 (2015)]. Here we analyze the field driven dynamics of such domain walls in permalloy strips of widths from 240 nm up to 6 $\mu$m, using the known equilibrium domain wall structures as initial configurations. Our micromagnetic simulations show that the domain wall dynamics in wide strips is very complex, and depends strongly on the geometry of the system, as well as on the magnitude of the driving field. We discuss in detail the rich variety of the dynamical behaviors found, including dynamic transitions between different domain wall structures, periodic dynamics of a vortex core close to the strip edge, transitions towards simpler domain wall structures of the multi-vortex domain walls controlled by vortex polarity, and the fact that for some combinations of the strip geometry and the driving field the system cannot support a compact domain wall.

Magnetization dynamics of imprinted non-collinear spin textures

We study the magnetization dynamics of non-collinear spin textures realized via imprint of the magnetic vortex state in soft permalloy into magnetically hard out-of-plane magnetized Co/Pd nanopatterned heterostructures. Tuning the interlayer exchange coupling between soft- and hard-magnetic subsystems provides means to tailor the magnetic state in the Co/Pd stack from being vortex- to donut-like with different core sizes. While the imprinted vortex spin texture leads to the dynamics similar to the one observed for vortices in permalloy disks, the donut-like state causes the appearance of two gyrofrequencies characteristic of the early and later stages of the magnetization dynamics. The dynamics are described using the Thiele equation supported by the full scale micromagnetic simulations by taking into account an enlarged core size of the donut states compared to magnetic vortices.

전해액 내 사카린의 농도 변화에 의한 전기도금 니켈-철 퍼멀로이 박막의 미세구조와 자기적 특성 변화

전기도금 니켈-철 퍼멀로이 박막에 대한 사카린의 영향에 대해 조사하였다. 1 <TEX>${\mu}mol/L$</TEX> 이하 농도의 사카린이 도금용 전해액에 첨가되면, 도금 박막의 결정립 크기를 감소시키고, 표면 거칠기를 낮추는 효과가 있다. 이러한 물성의 변화는 자기적 특성 중 보자력의 감소와 투자율과 자기임피던스의 증가로 나타난다. 결정립 크기의 감소는 증분투자율과 자기임피던스의 증가와 매우 밀접한 상관관계를 나타내고 있다. 사카린은 전기도금 연자성 퍼멀로이 박막에 유용한 첨가제이며 사카린의 농도변화로 연자성의 조절 가능성을 보였다. We studied the effects of Saccharin on the properties of electroplated Ni-Fe Permalloy thin films. When 0 to 1 <TEX>${\mu}mol/L$</TEX> of Saccharin was added to the plating electrolyte, the grain sizes of the deposits are found to decrease, which reduces the surface roughness and the coercivity and increases the permeability and magnetoimpedance. The reduction in the grain sizes is strongly correlated with increases in the incremental permeability and the magnetoimpedance. We demonstrated that Saccharine is a useful additive for the electrodeposition of soft Permalloy thin films and that the softness can be adjusted by varying the concentration of Saccharin.

Micromagnetic modelling of ferromagnetic cones

Using micromagnetic modelling, we calculate numerically the magnetization reversal of soft permalloy cones of height and diameter ⩽ 100 nm . By varying the cone height and the base diameter in steps of 10 and 5 nm, respectively, we map the remanent states systematically. We observe reversal mechanisms with remanent configurations ranging from single domains at small diameters, through buckle states and complex C-states through to vortex states at larger diameters and heights. We present a phase diagram of the remanent states of magnetization as a function of diameter and height. For the largest cones investigated, we find magnetization configurations in the reversal process which consist of two superimposed vortices with cores pointing in orthogonal directions.

Soft magnetic dot as a linear flux amplifier

It has been demonstrated that the critical current versus the applied flux relationship of an Al superconducting loop enclosing a soft Permalloy magnetic dot has a variable field-dependent phase. It is, therefore, possible to use this structure as a magnetic flux amplifier for applications in superconducting quantum interference devices. The dimensions of a single-domain Permalloy dot were selected in such a way that the preferential orientation of the magnetization is rotated from the perpendicular direction. By increasing an applied magnetic field, the magnetization of the dot rotates towards the out-of-plane direction. This magnetization rotation provides a flux gain and an enhancement of the field sensitivity. In the low-field regime, where the structure was investigated, the magnetization of the dot changes linearly with the applied flux and the flux gain is constant. As a result of a pronounced shape anisotropy, the flux gain can be tuned by adjusting the dimensions of the dot.

Comments on "Improving accuracy of intrinsic coercivity measurement for magnetically soft materials"

The authors of paper by Hilton et al. (see ibid., vol. 41. no. 8, P.2322-7, Aug. 2005) conclude among other things that the commercial imperative is to obtain accurate coercivity results. How slow does magnetizing field decay have to be in order to achieve this? There is no universal answer; it depends on material and on dimensions. For routine coercivity measurement of soft iron bars, a 60-s linear ramp time is advised. This protocol allows accurate coercivity measurement within an acceptable amount of laboratory time. The present author would like to mention that years ago a number of experiments were carried out indicating that coercivity of magnetically soft materials depends strongly on rate of rise of driving field. In case of a linear ramp driving held, coercivity, depends linearly on square root of this rate of rise, k/sub i/. It was shown experimentally that above dependence holds also for soft ferrites and Permalloy cores as well as for magnetic thin films.

Linear magnetic flux amplifier

By measuring the critical current versus the applied magnetic field Ic(Φ) of an Al superconducting loop enclosing a soft Permalloy magnetic dot, we demonstrate that it is feasible to design a linear magnetic flux amplifier for applications in superconducting quantum interference devices. The selected dimensions of a single-domain Permalloy dot provide that the preferential orientation of the magnetization is rotated from the perpendicular direction. By increasing an applied magnetic field, the magnetization of the dot coherently rotates toward the out-of-plane direction, thus providing a flux gain and an enhancement of the sensitivity. As a result of a pronounced shape anisotropy, the flux gain generated by the dot can be tuned by adjusting the dimensions of the dot.

Mobility of domain wall motion in the permalloy layer of a spin-valve-like [formula omitted] trilayer

The magnetization reversal of the magnetically soft permalloy ( Fe 20 Ni 80 ) layer in a spin-valve-like FeNi/Cu/Co trilayer was studied using photoelectron emission microscopy combined with X-ray magnetic circular dichroism, which allows to image the magnetic domain structure in an element-selective way. Nanosecond-short magnetic field pulses with amplitudes between 3.3 and 16.3 mT were applied one by one to reverse the magnetization of the FeNi layer. Images of the magnetic domain structure were taken after application of each pulse, and the mobility of magnetic domain wall motion in the FeNi layer was deduced. The reversal mechanism of the FeNi layer was found to depend on the applied pulse length, amplitude, and on the energy and direction of the coupling between the two ferromagnetic layers.

Magnetic force microscopy study of electron-beam-patterned soft permalloy particles: Technique and magnetization behavior

Electron-beam-patterned submicron permalloy elements with different aspect ratios were studied by magnetic force microscopy (MFM). The MFM tip stray field can be used to control a particle's magnetic state. By suitably choosing the operating mode and tip coatings, the tip induced distortion of the magnetic structure of soft permalloy elements can be largely reduced. The particle switching field can be precisely obtained by operating MFM at remanence. Through studying the remanent magnetization behavior, it was revealed that for large aspect ratio elements $(&gt;4:1)$ magnetization reversal occurs directly from one single domain state to the reversed single domain state, while for medium aspect ratio elements $(&lt;~4:1)$ the magnetization reversal occurs in a two-step process with two characteristic switching fields. Initially single domain particles switch into a low moment state (vortex state) at the first field ${H}_{\mathrm{s}},$ while at the higher field ${H}_{\mathrm{a}},$ the magnetic moments form a reversed single domain state. The forming of the low moment state is due to the fact that the vortex states can be trapped in the elements during magnetization reversal. This is consistent with micromagnetic simulations and can be directly demonstrated by controlled local MFM tip induced switching. The variations in the measured distribution of the switching fields for both large and small aspect ratio particle arrays are attributed to different reversal mechanisms as well as individual difference in size, thickness, and edge roughness.