Permanent Magnet Layer Research Articles

Covalent Organic Frameworks with Tunable Chirality for Chiral-Induced Spin Selectivity.

Chiral covalent organic frameworks (CCOFs) have attracted extensive interest for their potential applications in various enantioselective processes. However, the exploitation of chirality-induced spin selectivity (CISS) that enables a new technology for the injection of spin polarized current without the need for a permanent magnetic layer within CCOFs remains a largely untapped area of research. Here, we demonstrate that, for the first time, COFs can be an attractive platform to develop spin filter materials with efficient CISS. This facilitates the design and synthesis of a new family of Zn(salen)-based 2D CCOFs, namely, CCOFs-9-12, by imine condensation of chiral 1,2-diaminocyclohexane and tri- or tetra(salicylaldehyde) derivatives. CCOF-9, distinguished by its unique C2 symmetric "armchair" tetrasubstituted pyrene conformation, exhibits the most pronounced chirality among these materials and serves as a solid-state host, enabling the enantioselective adsorption of racemic drugs with an enantiomeric excess (ee) of up to 97%. After substituting diamagnetic zinc(II) ions for paramagnetic cobalt(II), the resulting CCOF-9-Co not only retains its high crystallinity, porosity, and exceptional chirality but also exhibits enhanced conductivity, a crucial factor for the effective observation of CISS. Magnetic conductive atomic force microscopy showed that CCOF-9-Co exhibited a remarkable CISS effect with up to an 88-94% spin polarization ratio. This phenomenon is further confirmed by the increased intensity in the magnetic circular dichroism (MCD) when CCOF-9-Co is under an external magnetic field. This work therefore shows the tremendous potential of CCOFs for controlling spin selectivity and will stimulate the creation of new types of crystalline polymers with strong CISS effects for spin filters.

Compact lightweight magnetic gripper designed for biped climbing robots based on coaxial rotation of multiple magnets

Biped climbing robots can move and work in three-dimensional steel structures, but are extremely sensitive to the weight, size, and adsorption performance of the devices attached at both their ends. Herein, we propose a novel gripper for biped climbing robots comprising two layers of multiple fan-shaped permanent magnets, wherein the upper layer can coaxially rotate with respect to the lower layer. The novel magnetic gripper can switch between the release and adsorption states by rotating the upper layer of magnets to a particular angle, and it can approximately linearly control the adsorption force by varying this rotation angle. The structural parameters and layout of the magnets were studied and optimized, and the adsorption characteristics of the gripper were analyzed via simulations and verified via experiments. Additionally, the proposed magnetic gripper was applied in a biped climbing robot for verifying the effectiveness of the design based on three climbing tests. The results revealed that the proposed magnetic gripper outperformed the existing models in terms of adsorption force to mass ratio. The proposed gripper design offers the advantages of compact structure, simple control, and natural self-locking of the release and adsorption states.

편심 자석 로터의 내·외측 자기장 변조를 이용한 마그네틱 하모닉 기어

In a magnetic harmonic gear, the magnetic field on the high-speed side is modulated by the air-gap movement according to the rotation of the eccentric body. Owing to the modulated magnetic field, the permanent magnet layer outside the high-speed rotor rotates in synchronization with the stator composed of another permanent magnet. Therefore, transferring only the synchronous rotational motion outside the eccentric body to the output side requires a complicated conversion mechanism. In this study, we propose a magnetic harmonic gear that utilizes both the inner and outer magnetic fields of an eccentric permanent magnet layer. The outer magnetic field is utilized for the deceleration function as in the existing harmonic gear, whereas the additional inner magnetic field is utilized to extract the rotational motion. The topology of the system is verified by the harmonic analysis of the air-gap magnetic field and with experimental set-up.

Design of an Electromagnetic Energy Harvesting System Applied to Shock Absorber in Sport Utility Vehicle : Part II. Improvement of The Power & Power Density

To harvest the kinetic energy from the vehicle suspension system, a tubular generator, which is composed of a single permanent magnet layer coreless model, was proposed in the previous study. Despite the excessive volume of the generator, both output power and power density are significantly lower than other conventional machines. This paper examines different designs of the tubular generator with the goal to enhance the performance, including a double permanent magnet layers coreless model and a cored model. By using a commercial finite element method (FEM) software, two proposed generators are theoretically analyzed and compared with the conventional generator. Analyzed results reveal that under the same operating conditions, the cored model can regenerate the largest amount of the power density. These results indicate that cored model can be considered as a promising candidate for the application to the electromagnetic shock absorber in sport utility vehicle (SUV).

Design of An Electromagnetic Energy Harvesting System Applied to The Shock Absorber of A Sport Utility Vehicle : Part I. Single Permanent Magnet Layer Coreless Type

This paper deals with the design of an electromagnetic energy harvesting generator for the suspension system of a sport utility vehicle. The proposed generator is composed of a single coreless type permanent magnet layer, which increases flux density across the coil windings and eliminates flux leakage by using the Halbach PM array, thus improving the machine’s performance, including flux linkage and output power. The goal of the system is to regenerate energy from the kinetic energy of the suspension system of the sport utility vehicle. The proposed generator physically combines electrical and mechanical components, in which permanent magnets, coil windings, and back iron are attached to the body of the shock absorber. The design’s performance was investigated using the finite element method (FEM) and validated by comparison with experimental data.

이축 방향의 복합 자기 경로를 갖는 마그네트 기어

A magnet gear composed of two layers of permanent magnets repeated circumferentially can transmit the power without mechanical contact. In the topology called by the magnet shutter gear known as the most competitive concept among the existing concepts, the number of pole-pairs on the high speed rotor corresponds to that of low speed rotor through electric steel set functioning as a magnetic modulator. The methodology is classified into radial type and axial type according to its magnetic path as in the motor. However, the magnetic modulator has multiple poles located separately. So, it is very complicated to assemble each module of the magnet gear mechanically and to sustain a mechanical stiffness of the modulator. The practical trouble can be solved partially through reconfiguring the modules. This paper deals with the novel magnetic shutter gear topology varying the magnetic path and its effectiveness is verified through real hardware implementation.

Removal of Particulate Matter Emitted from a Subway Tunnel Using Magnetic Filters

We removed particulate matter (PM) emitted from a subway tunnel using magnetic filters. A magnetic filter system was installed on the top of a ventilation opening. Magnetic field density was increased by increasing the number of permanent magnet layers to determine PM removal characteristics. Moreover, the fan's frequency was adjusted from 30 to 60 Hz to investigate the effect of wind velocity on PM removal efficiency. As a result, PM removal efficiency increased as the number of magnetic filters or fan frequency increased. We obtained maximum removal efficiency of PM10 (52%), PM2.5 (46%), and PM1 (38%) at a 60 Hz fan frequency using double magnetic filters. We also found that the stability of the PM removal efficiency by the double filter (RSD, 3.2-5.8%) was higher than that by a single filter (10.9-24.5%) at all fan operating conditions.

Electroplated Magnet Membranes for MEMS Applications

The influence of a magnetic field on electrodeposition of nickel films over polymeric substrates which renders flexible membranes with permanent magnet layers is studied. Samples of membranes with nickel deposited by electroplating in presence and absence of magnetic field are compared. To improve adherence, the electroplated layer is deposited over an electroless contact layer, after a wet pre-treatment. Mechanical and magnetic properties of the samples were measured as function of process parameters. Experimental results confirm that the magnetic field has a positive impact over properties of deposited films.

Electroplated Nickel Permanent Magnetic Films over Polymeric Membranes

The influence of a magnetic field on electrodeposition of nickel films over polymeric substrates, which renders flexible membranes with a permanent magnet layer, has been studied. Samples of membranes with nickel deposited by electroplating in presence and absence of magnetic field are compared. The electroplated layer is deposited over an electroless contact layer, after a wet pre-treatment to improve adherence. Mechanical and magnetic properties of the samples were measured as function of process parameters. Experimental results confirm that the magnetic field has a positive impact over properties of deposited films. Pre-treatment using different process times influences uniformity and adherence of the deposited films. Results show also that films electroplated in presence of magnetic field outperformed those deposited in its absence, with enhanced maximum energy product and reduced surface roughness. On the other hand, films electroplated in presence of magnetic field tend to be less resistant to fracture during flexure tests.

Active vibration control of plates using electro-magnetic constrained layer damping

This paper investigates vibration control of beam through electro-magnetic constrained layer damping (EMCLD) which consists of electromagnet layer, permanent magnet layer and viscoelastic damping layer. When the coil of the electromagnet is electrified with proper control strategy, the electromagnet can exert magnetic force opposite to the direction of structural deformation so that the structural vibration is attenuated. A mathematical model is developed based on the equivalent current method to calculate the electromagnetic control force produced by EMCLD. The governing equations of the system are obtained using Hamilton’s Principle and then reduced with the assumed-mode method. A simulation on vibration control of a cantilever beam is conducted under the velocity proportional feedback to demonstrate the energy dissipation capability of EMCLD, and the beam system with the same parameter is experimented. The results of experiment and simulation are compared and the results show that the EMCLD is an effective means for suppressing modal vibration. The results also indicate that the beam system has better control performance for larger control current. The EMCLD method presented in this paper provides an applicable and efficient tool for the vibration control of structures.

Hybrid Vibration Control of a Circular Cylindrical Shell Using Electromagnetic Constrained Layer Damping Treatment

This paper investigates hybrid vibration control of a circular cylindrical shell through electromagnetic constrained layer damping (EMCLD) treatment, which consists of an electromagnet layer, a permanent magnet layer and a sandwiched viscoelastic damping layer. A mathematical model is developed based on the equivalent current method to calculate the electromagnetic control force produced by EMCLD. The governing equations of the shell system are established using Hamilton’s principle and then reduced with the assumed-mode method. The vibration control of a clamped-free circular cylindrical shell is simulated with velocity-proportional feedback to demonstrate the energy dissipation capability of EMCLD. Also, parametric studies are performed to examine the influences of geometry and physical properties of EMCLD on control performance. The results show the distinct energy consumption function of EMCLD in the passive way. The hybrid way provides much better control performance than the passive way in the concerned frequency range. It is also indicated from parametric studies that increasing the value of any one of the physical parameters, such as the loss factor of the viscoelastic material, the thickness of the permanent magnet and the area of EMCLD, has a contribution to the improvement of hybrid control performance. In contrast, increasing the thickness of the viscoelastic layer deteriorates both passive and hybrid control effects.

Enhancement of Magnetostriction in Internally-Biased Terfenol-D 2-2 Composites

A key issue in the fabrication of Terfenol-D 2-2 composites with internal magnetic field biasing is the selection of appropriate constituent materials to obtain high magnetostriction while keeping optimum magnetomechanical properties. The fabrication process is costly and time consuming and, therefore, numerical methods to predict their properties are useful. In this paper, finite element analysis (FEA) of the magnetostriction of such composites has been carried out using the commercial package ABAQUS. It has been shown that composites fabricated using Nd2Fe14B for the permanent magnetic material layers possess the highest internal fields within the Terfenol-D layers, although the overall strain of these composites is limited to approximately 800 times 10-6 due to the high elastic modulus of Nd2Fe14B. Simulations showed that the strain can be enhanced by choosing a different material with a lower elastic modulus for the permanent magnetic layer even though the internal field is lower. The simulations showed that the strain can increase by 12% if the Nd2Fe14B layer is substituted by SmCo5; by 23 % if it is substituted by Sm2Co17; and by 35 % if it is substituted by Alnico.

Active Vibration Control of Beam Using Electro-magnetic Constrained Layer Damping

This paper investigates vibration control of beam through electro-magnetic constrained layer damping (EMCLD) which consists of electromagnet layer, permanent magnet layer and viscoelastic damping layer. When the coil of the electromagnet is electrified with proper control strategy, the electromagnet can exert magnetic force opposite to the direction of structural deformation so that the structural vibration is attenuated. A mathematical model is developed based on the equivalent current method to calculate the electromagnetic control force produced by EMCLD. The governing equations of the system are obtained using Hamilton's Principle and then reduced with the assumed-mode method. A simulation on vibration control of a cantilever beam is conducted under the velocity proportional feedback to demonstrate the energy dissipation capability of EMCLD, and the beam system with the same parameter is experimented. The results of experiment and simulation are compared and the results show that the EMCLD is an effective means for suppressing modal vibration. The results also indicate that the beam system has better control performance for larger control current. The EMCLD method presented in this paper provides an applicable and efficient tool for the vibration control of structures.

Thin film SmCo magnets for use in electromagnetic microactuators

Efficient magnetic microactuators require a deposition and patterning of a permanent magnetic material. A material that can be deposited in the range of up to a couple of 10μm is sputtered SmCo. For the fabrication of magnetic microactuators, alternative substrate materials besides silicon are of great interest. Therefore, alumina-ceramic as well as B270-glass substrates were included in the investigation. A maximum energy product of 90kJ∕m3 was achieved for rather thick layers of 30μm deposited on glass or ceramic substrates. The latter substrates were found to be suitable for the deposition of SmCo layers up to a thickness of 50μm. Furthermore, the SmCo exhibits isotropic magnetic properties, thus a magnetization of the permanent magnetic layer can be performed in plane as well as perpendicular to the film plane. For the patterning of these thick SmCo layers ion beam etching and wet chemical etching were examined. For both methods, the suitability of patterning thick SmCo layers could be demonstrated. For the integration of a SmCo permanent magnet in a magnetic microactuator, the two technologies for deposition and patterning of the SmCo layer had to be combined. Two linear microactuators are presented utilizing different integration methods of the SmCo component as well as direction of magnetization.

The magnetic properties of sputter-deposited and annealed CoCr/CoCrPt recording media

CoCr and CoCrPt thin films on Cr or CrTi underlayers were studied to improve the magnetic properties for permanent magnetic stabilization layer application in anistropic magnetoresistance/giant magnetoresistance devices. Their structural and magnetic properties were investigated as a function of Pt content in magnetic layer, Ar gas pressure, Cr underlayer thickness or Ti content of CrTi underlayer and post-deposited annealed temperature. High coercivity Hc values (2000Oe) can be achieved even remanence-thickness product (Mrδ) less than 1memu/cm2 during room temperature deposited using proper magnetic alloy and deposition processes. Post-deposited annealed further improved the coercivity of the cobalt films up to 3500Oe as Mrδ was reduced from 1.2 to 0.5memu/cm2.

Domain control in magnetic shields using patterned permanent magnet underlayer

The domain state of a magnetic shield in a recording head can be controlled by an adjacent patterned permanent magnet layer. A 1.1-μm-thick electroplated Ni80Fe20 (NF) film with slight uniaxial magnetic anisotropy was patterned into rectangular magnetic shields with various dimensions over patterned thin film made from a 0.1-μm-thick CoCrPt permanent magnet (PM). The shape of the adjacent biasing PM layer should be the shape of a desired final domain in NF. Domain structure in the NF layer and the process of magnetic saturation were imaged using wide-field Kerr microscopy. The NF and PM layers are magnetically coupled and, therefore, a magnetic state with parallel magnetization is preferred. The PM direction of magnetization is set in high magnetic field and the final NF domain state is controlled by the shape of PM features. The simplest stable domain structure in a rectangular thin shield is of an “envelope” type. Using a PM underlayer, either clockwise or counterclockwise domain structure is preferred. Various resulting domain structures were studied after saturation in various magnetic fields and a range of directions. While the resulting domain structures in NF are regular and well defined after saturation in a large magnetic field, more complex and irregular structures are generated in NF after magnetization in a smaller field. Domain structures for various field treatments are discussed.

Spin-valve heads with self-stabilized free layer by antiferromagnet

We demonstrate the feasibility of a spin-valve read head using an adjacent antiferromagnetic (AFM) layer to provide a stabilization Held, eliminating the hard bias permanent magnet layer. The head stack consists of seed/AFM/CoFe/Ru/CoFe/Cu/CoFe (and/or NiFe)/Cu/IrMn/cap where the AFM is PtMn or IrMn. The abutted junction is about 0.1 /spl mu/m wide at the free layer and no permanent magnet materials are used. Micromagnetic modeling indicates that a proper bias field is needed to have a stable head response. The bias field from the AFM layer can be modified by a nonmagnetic spacer layer between AFM and FM. The coupling field decays exponentially with the thickness of the spacer layer, consistent with a pinhole-dominated mechanism. Unshielded sensors show much higher sensitivity as,compared with a standard PM abutted junction head. Microtrack profile based on the spin-stand test shows a regular shape without apparent lumps. The electrical reader width is about 6 /spl mu/" (0.15 /spl mu/m), corresponding to a track density of 112 ktpi. Combined with a linear density of 591 kbpi the heads in this work are capable of areal density around 66 Gb/in/sup 2/.

An analysis of passive magnetic composites for suppressing the vibration of beams

The fundamentals of controlling the structural vibration of beams treated with a new class of Passive Magnetic Composites (PMC) are studied. The PMC is a constrained damping treatment, where a viscoelastic core is sandwiched between two layers of permanent magnets. The interaction forces between the magnets aim at enhancing the damping characteristics of the viscoelastic. The effectiveness of such treatments is demonstrated both numerically and experimentally. In particular, a finite element code is developed to model the interaction between the dynamic behavior of the beam, the viscoelastic layer and magnetic layers. The model is validated experimentally at various operating conditions and the performance of the treatment is evaluated for different configurations of the magnetic layers. The obtained results suggest the potential of the new class of PMC as an effective and simple mean for controlling structural vibrations.

Ion beam deposition processes for improved hard bias magnetic and device properties in the abutted junction configuration

Permanent magnet films of Cr/CoCrPt for use in an abutted junction hard bias scheme were deposited by an ion beam deposition (IBD) system. The deposition angle control of IBD systems was employed to yield some excellent material and device related improvements. For films with the structure Cr-50 Å/CoCrPt-250 Å, increasing the deposition angle θ (as measured from the substrate normal) of the Cr layer from 20° to 60°, resulted in an increase in coercivity from 1860 to 1905 Oe. X-ray diffraction measurements showed that this improvement was related to an increase in CoCrPt in-plane texture and a decrease in c-axis perpendicular texture. The reason for this increase in in-plane texture is that there is better epitaxial matching between the CoCrPt and the Cr underlayer brought about by a change in the lattice dimension of Cr as a result of changing stress levels. Another positive effect of depositing the Cr at a larger angle is that the Cr would be thicker farther into the abutted junction and thus delay the onset of poor magnetic properties due to a thinning underlayer. The angle of deposition parameter can be used to further advantage by depositing the lead layer at a larger angle than the permanent magnet layers. This type of scheme would allow the leads to encroach over the permanent magnets and make direct contact with the sensor, yielding low contact resistance.

Ion beam deposition of permanent magnet layers for liftoff processes

Thin film permanent magnet layers of Cr/CoCrPt were prepared by ion beam deposition in a Veeco IBD-350 tool. The magnetic properties were measured as a function of deposition angle, deposition energy, assist energy, and the underlayer and permanent magnet thicknesses. It was found that higher deposition energies and angles (from normal) resulted in larger coercivities. Increasing the assist energy also helped increase the coercivity. The coercivities were in the range of 1400–2100 Oe depending on the deposition conditions, for a Cr-50 Å/CoCrPt-250 Å film. The squareness, S (the ratio of remnant magnetization to saturation magnetization) and Mrt (remnant magnetization and film thickness product) for these films were about 0.85 and 1.3 memu/cm2, respectively. It was found that underlayers of Cr as thin as 25 Å could be used, without significant degradation of magnetic properties. The coercivity had a broad peak between 100 and 200 Å of CoCrPt, above which the coercivity gradually decreased. θ–2θ x-ray diffraction measurements showed the presence of in-plane textures of (101̄0) and (112̄0) with the largest coercivity being obtained when a strong (101̄0) peak is observed. The side-wall profile of the permanent magnet, measured after a liftoff process, was found to depend on the deposition angle. As the angle got larger (further away from normal incidence), the side wall showed greater tapering. This is due to the increased effect of shadowing by the photoresist structure. The directional, collimated, nature of the deposition beam was found to aid the liftoff process, by avoiding step coverage of the liftoff structures. This significantly increased the ease of lifting off. By adjusting the deposition angle, it is possible to tailor the process to provide optimum magnetic properties, coupled with good electrical contact. Thus, it was found that ion beam deposition is an attractive alternative to sputter deposition (physical vapor deposition), providing some important advantages over it.