Permanent Magnet Properties Research Articles

Permanent magnetic properties of NdFe12Nx sputtered films epitaxially grown on V buffer layer

To clarify the magnetic properties of the NdFe12Nx compound, which shows promise as a high-performance permanent magnet material, NdFe12Nx epitaxial films fabricated by using a V underlayer on MgO (100) single-crystalline substrates were investigated. Nd-Fe films deposited on a V underlayer consist of NdFe12 grains, which have a c-axis orientation perpendicular to the film plane, as well as α-Fe and Nd2Fe17 phases. In the Nd-Fe-N film obtained by subsequent nitridation of the Nd-Fe film, NdFe12Nx grains grew as the dominant phase, and the volume fractions of α-Fe phases dropped below 5%. A Nd-Fe-N film with a thickness of 50 nm exhibits a saturation magnetization (Ms) of 1.7 T, an anisotropy field (HA) of ∼60 kOe, a magnetocrystalline anisotropy energy (K1) of ∼4.1 MJ/m3, and a coercivity (Hc) of 1.7 kOe. The Hc of a Nd-Fe-N film with a thickness of 25 nm is 4.3 kOe. These results indicate that NdFe12Nx compounds have a superior Ms compared to Nd-Fe-B magnets, while the enhancement in Hc is indispensable.

A Study of the Causes of Failure of Permanent Magnets from Cast Hard Magnetic Alloys

The microstructure and magnetic properties of permanent magnets fabricated from cast hard magnetic alloys of the Fe – Ni – Al system with cobalt addition of type YuNDK are studied. The causes of failure of such magnets in operation are determined. Recommendations are given for correcting the melting process and the modes of heat treatment of magnets in order to provide the required properties without disturbing the integrity of the magnets.

Magnetic ordering of Mo2NiB2-type {Gd, Tb, Dy)2Co2Al compounds by magnetization and neutron diffraction study

The magnetic ordering of Mo2NiB2-type {Gd, Tb, Dy}2Co2Al (Immm, No. 71, oI10) compounds has been established using bulk magnetic measurements and neutron diffraction study. Polycrystalline Gd2Co2Al, Tb2Co2Al and Dy2Co2Al undergo ferrimagnetic transitions (TC) at 78K, 98K and 58K, respectively, and low-temperature field induced transition (Tm) around 15K, 20K and 15K, respectively. Between Tm and TC Gd2Co2Al, Tb2Co2Al and Dy2Co2Al are soft ferrimagnets. Below Tm Gd2Co2Al is soft ferrimagnet, whereas Tb2Co2Al and Dy2Co2Al exhibit permanent magnet properties with residual magnetization per rare earth of 4.95B and 4.8B, respectively, and large coercive field of 72kOe and 22kOe, respectively, at 2K.The magnetocaloric effects of Gd2Co2Al, Tb2Co2Al and Dy2Co2Al were calculated in terms of isothermal magnetic entropy change and they reach maximum values of −10.4J/kgK, −7.6J/kgK and −6.6J/kgK for a field change of 50kOe near 75K, 98K and 58K, respectively. Low-temperature transition of Gd2Co2Al is followed by the magnetic entropy change of −2.9J/kg K in a field change of 50kOe at 15K. Low temperature magnetic ordering with enhanced anisotropic effects in Tb2Co2Al and Dy2Co2Al is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +19.9J/kgK at 20K (field change 0–50kOe) and +2.7J/kgK at 15K (field change 0–10kOe), respectively.Neutron diffraction study shows that, in zero applied field, Tb2Co2Al exhibits c-axis ferrimagnetic ordering with magnetic space group Immm′ and propagation vector K0=[0, 0, 0] below TCND∼111K with MTb=8.86(15)B and MCo=0.26(2)B at 2K.

Effect of surfactants on wet grinding of barium hexaferrite powders and on the microstructure of sintered magnets on their basis

The effect of citric acid and isopropyl alcohol on the wet grinding of the mixture of initial ferriteforming components and synthesized ferrite charge has been analyzed. It has been established that the introduction of admixtures during wet grinding makes it possible to substantially reduce the ferrite synthesis temperature and the sintering temperature of green billets and to improve the magnetic properties of permanent magnets made of barium ferrites by the formation of a dense, fine-grained structure. The increase in the activity of powders is explained by the formation of active jelly-like interlayers on the surfaces of particles during wet grinding.

Nd2Fe14C-based magnet with better permanent magnetic properties prepared by a simple mechanochemical method

Nd2Fe14C-based magnet is prepared by a mechanochemical method, namely high-energy ball-milling Nd2Fe11Bx (x=0–0.15) alloy in heptane (C7H16), followed by annealing to 850°C in vacuum. Under the action of high-energy ball-milling, Nd2Fe11Bx react with heptane to form NdH2+δ, Fe-(CB), C, etc. H2 is released and Nd2Fe17, Nd2Fe17Cx (x=0–3), Nd2Fe14C, Nd carbides and α-Fe are formed in the subsequent annealing. C amount depends on ball-milling time t. Long time ball milling or high C content suppresses the formation of 2:17 phase and favors the formation of 2:14:1 phase in the final products. Excessive ball-milling results in the quick increase of α-Fe. The maximum of magnetically hard Nd2Fe14C is obtained at t=4h. For Nd2Fe11 samples, there exists considerable quantity of Nd carbides and α-Fe phase appears earlier and increases rapidly with extending the ball-milling time t. The addition of B element shortens the ball-milling time of the formation of maximum Nd2Fe14C and prominently suppresses the formation of Nd carbide and α-Fe. The optimum magnetic properties, coercivity iHc of 1193.7kA/m, remanence Mr of 580.9kA/m, maximum magnetic energy product (BH)max of 91.7kJ/m3 is approaching to its theoretic value of 99.2kJ/m3 for isotropic Nd2Fe14C magnet, are obtained in Nd2Fe11B0.06 alloy ball milled for 3.5h.

Nonlinear conjugate gradient methods in micromagnetics

Conjugate gradient methods for energy minimization in micromagnetics are compared. The comparison of analytic results with numerical simulation shows that standard conjugate gradient method may fail to produce correct results. A method that restricts the step length in the line search is introduced, in order to avoid this problem. When the step length in the line search is controlled, conjugate gradient techniques are a fast and reliable way to compute the hysteresis properties of permanent magnets. The method is applied to investigate demagnetizing effects in NdFe12 based permanent magnets. The reduction of the coercive field by demagnetizing effects is μ0ΔH = 1.4 T at 450 K.

Microstructures, physical and magnetic properties of BaFe12O19 permanent magnets with the addition of Al2O3-MnO

Barium hexaferrite (BaFe12O19) permanent magnets with the addition of Al2O3-MnO (0.12, 0.24; and 0.42 wt%) have been prepared by mechanical alloying method. The addition of Al2O3-MnO was done in order to improve the density and mechanical properties of the fabricated BaFe12O19 permanent magnet. Particle size of the as-mixed powder decreases Al2O3-MnO concentration increases. The as-mixed powders was then compacted into pellets and sintered at 1000 and 1100 °C for 2 hours. The crystalline phases and morphology of the pellets were observed using X-ray diffraction (XRD) and Scanning electron microscopy (SEM), respectively. It is found that the increase of the sample hardness has correlation with the bulk density of the samples. While, the flux density decreases linearly as Al2O3- MnO additives increases. The analysis of hysteresis curves classified the pellets as a hard magnet.

Magnetization reversal processes of isotropic permanent magnets with various inter-grain exchange interactions

We performed a large-scale micromagnetics simulation on a supercomputing system to investigate the properties of isotropic nanocrystalline permanent magnets consisting of cubic grains. In the simulation, we solved the Landau–Lifshitz–Gilbert equation under a periodic boundary condition for accurate calculation of the magnetization dynamics inside the nanocrystalline isotropic magnet. We reduced the inter-grain exchange interaction perpendicular and parallel to the external field independently. Propagation of the magnetization reversal process is inhibited by reducing the inter-grain exchange interaction perpendicular to the external field, and the coercivity is enhanced by this restraint. In contrast, when we reduce the inter-grain exchange interaction parallel to the external field, the coercivity decreases because the magnetization reversal process propagates owing to dipole interaction. These behaviors show that the coercivity of an isotropic permanent magnet depends on the direction of the inter-grain exchange interaction.

Remote Temperature Distribution Sensing Using Permanent Magnets

Remote temperature sensing is essential for applications in enclosed vessels, where feedthroughs or optical access points are not possible. A unique sensing method for measuring the temperature of multiple closely spaced points is proposed using permanent magnets and several three-axis magnetic field sensors. The magnetic field theory for multiple magnets is discussed and a solution technique is presented. Experimental calibration procedures, solution inversion considerations, and methods for optimizing the magnet orientations are described in order to obtain low-noise temperature estimates. The experimental setup and the properties of permanent magnets are shown. Finally, experiments were conducted to determine the temperature of nine magnets in different configurations over a temperature range of 5 °C to 60 °C and for a sensor-to-magnet distance of up to 35 mm. To show the possible applications of this sensing system for measuring temperatures through metal walls, additional experiments were conducted inside an opaque 304 stainless steel cylinder.

Hf2Co11 thin films: Rare-earth-free permanent nanomagnets

Hf2Co11 thin films were deposited on single crystalline Si(100) substrates by using conventional direct current (DC) magnetron sputtering with a Hf2Co11 alloy target. All films were grown at room temperature with 120W sputtering power. In order to obtain the composition of the desired, the working pressure was changed from 0.66 to 1.05Pa. The relationships between structural and magnetic properties in Hf-Co films were studied by using differential thermal analyzer, glancing incidence X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, atomic force microscopy, magnetic force microscopy and vibrating sample magnetometer. It revealed that the as-deposited films were amorphous at room temperature for all deposition pressures and showed soft ferromagnetic phase. In order to increase the coercive field associated with an advancing transition to hard phase, thin films were post-annealed from 773K to 973K. Post-annealing process led to a high remanence magnetization and improved the squareness of the demagnetization curve. Their saturation magnetization values varied from 515 to 1378kA/m and also coercive field values varied from 52x10−4 to 153x10−3 T at room temperature depending on post-annealing temperatures. Hf2Co11 soft ferromagnetic phase was modified by formation of post-annealing and was given rise to enhance permanent magnet properties (saturation magnetization, coercive field, energy product). The magnetic properties of thin films were found to be convenient for nanomagnet applications.

Titanium substituted manganese-ferrite as an oxygen carrier with permanent magnetic properties for chemical looping combustion of solid fuels

Mixed oxides of Mn-Fe have been identified as suitable materials for Chemical Looping Combustion (CLC) with solid fuels both via in-situ Gasification Chemical Looping Combustion (iG-CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) processes. These materials show the property of react with gaseous fuels as well as release oxygen under given conditions, while cheap metals are used. In addition, these materials can show magnetic properties that can be used for an easy separation from ash in CLC with solid fuels. Thus, losses of oxygen carrier material in the ash drain stream would be reduced. Different cations have been proposed for improving the magnetic properties of manganese ferrites, including Ti4+. In this context, the present work accomplishes a screening of (MnxFe1−x)2O3 doped with 7wt.% TiO2, with x ranging from 0 to 1. The influence of Mn:Fe ratio on their physical and chemical properties was evaluated. In general, particles with high crushing strength values (>4N) were obtained, and magnetic characteristics were highlighted when x⩽0.66. The oxygen uncoupling capability depended on the Mn:Fe ratio and the oxidation conditions, i.e. temperature and oxygen partial pressure. Broader oxidation conditions to take advantage of the oxygen uncoupling capability were found for materials with low Mn content. On contrary, the reactivity with fuel gases (CH4, H2 and CO) increased with the Mn content. Thus, oxygen carriers with Mn/(Mn+Fe) molar ratio in the 0.5–0.9 interval showed interesting properties at suitable temperatures for the iG-CLC and CLOU processes (i.e. 850–980°C). The material with Mn/(Mn+Fe)=0.55 was preferred considering a trade-off between reactivity and magnetic properties.

Electric field control of magnetic properties of Nd2Fe14B thin films grown onto PMN-PT substrates

Nd2Fe14B films with easy magnetization axis perpendicular to the film plane were grown onto Ta-buffered piezoelectric (011)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) substrates using a magnetron sputtering technique. The film retains good permanent magnetic properties, with coercivities up to 1.4 T and spin reorientation near 150 K. Our investigations demonstrated that the converse piezoelectric effect generated by an electric field across the PMN-PT substrate can rotate the angle of spin reorientation of the Nd2Fe14B films, resulting in a considerable manipulation of magnetization by the electric field at temperatures below 150 K. The ratio of magnetization change reaches 30% in a magnetic field of 2 T when an electric field of 6 kV/cm is applied at 30 K. With increasing temperature, the electric field-induced tunability of magnetization decreases. These observations of permanent magnetic properties and electrically controlled magnetization effects make the Nd2Fe14B/PMN-PT heterostructure attractive for exploring multifunctional magnetic/electric devices.

Irradiation effect of Sm2Co17 type permanent magnets

Insertion devices are crucial parts of the third generation of synchrotron radiation facility and free electron laser devices. The use of insertion device can improve the brightness and coherence of synchrotron radiation light. Undulator, one kind of insertion device, is largely installed in the storage ring of Shanghai synchrotron radiation facility. The main part of undulator is the device of magnetic source which consists of periodically arranged permanent magnets with the same magnetic field strength. In order to keep the normal electronic trajectory, a stable magnetic intensity in undulator is required. The Sm2Co17 type permanent magnets with high intrinsic coercive force and good radiation stability are largely installed in the facility. However, the losses for magnetic properties of Sm2Co17 type permanent magnets can be induced by longperiod irradiation in undulator through beam loss or mis-steering. The reduction of magnetic field could affect the electron energy, direction and the movement trajectory and so on, which seriously affects the amount of synchrotron radiation light. Microstructure of Sm2Co17 type permanent magnet affects the macro magnetic properties and there is not any available report on the microstructure investigation of Sm2Co17 type permanent magnet after being irradiated. Therefore, in this work, the effect of irradiation on the microstructure evolution is investigated. The radiation fields of Sm2Co17 type permanent magnets and the main particles (neutron) that result in losing magnetic properties are first analyzed and confirmed by Monte Carlo code FLUKA calculation. Then, Sm2Co17 type permanent magnet samples are irradiated by Ar ions at different fluences to simulate neutron irradiation damage. Meanwhile, the microstructure evolutions of irradiated samples are characterized by transmission electron microscopy. Moreover, high resolution transmission electron microscopic images are taken at the peak of radiation damage field to further investigate the radiation damage. In the respect of macro magnetic properties, hysteresis loops are measured by vibrating sample magnetometer in order to study the change of saturated magnetization. The results indicate that the decrease of saturated magnetization value is related to the change of microstructure, which proves the speculation of previous investigations. The evolution of 2:17 phase transformed from single crystals into amorphous structure is a possible microscopic mechanism for irreversible loss for saturated magnetization of Sm2Co17.

Influence of Permanent Magnet Properties and Arrangement on Performance of IPMSMs for Automotive Applications

Interior permanent magnet synchronous motors (IPMSMs) are widely utilized as traction motors. The permanent magnets (PMs) used in IPMSMs are an important factor; thus, high-coercivity PMs with lesser rare-earth elements are in development. This paper investigates the performance of IPMSMs typically used in automotive applications that were modified to contain a novel magnet model (NMM). Rotor models with two PM arrangements, a V-shaped single-layered PM structure (Type 1V) and a double-layered PM structure (Type 2D), were considered in this study. This paper discusses the characteristics of the analysis models based on the results of two-dimensional finite element analysis. The maximum torques of Types 1V and 2D with the NMMs were approximately the same. In addition, the loss of Type 2D with the NMM was lower than that of Type 1V with the NMM at two evaluation points and under two driving schedules. Therefore, Type 2D was proved to be suitable for use with NMMs.

CeNi3-type rare earth compounds: crystal structure of R3Co7Al2 (R=Y, Gd–Tm) and magnetic properties of {Gd–Er}3Co7Al2, {Tb, Dy}3Ni8Si and Dy3Co7.68Si1.32

The crystal structure of new CeNi3-type {Y, Gd–Tm}3Co7Al2 (P63/mmc. N 194, hP24) compounds has been established using powder X-ray diffraction studies. The magnetism of Tb3Ni8Si and Dy3Ni8Si is dominated by rare earth sublattice and the magnetic properties of R3Co7Al2 (R =Gd–Er) and Dy3Co7.68Si1.32 are determined by both rare earth and cobalt sublattices. Magnetization data indicate ferromagnetic ordering of {Tb, Dy}3Ni8Si at 32K and 21K, respectively. Gd3Co7Al2 and Tb3Co7Al2 exhibit ferromagnetic ordering at 309K and 209K, respectively, whereas Dy3Co7Al2, Ho3Co7Al2, Er3Co7Al2 and Dy3Co7.68Si1.32 show a field dependent ferromagnetic-like ordering at 166K, 124K, 84K and 226K, respectively followed by a low temperature transition at 34K for Dy3Co7Al2, 18K for Ho3Co7Al2, 56K for Er3Co7Al2, 155K and 42K for Dy3Co7.68Si1.32. Among these compounds, Dy3Ni8Si shows largest magnetocaloric effect (isothermal magnetic entropy change) of −11.6J/kg·K at 18K in field change of 50kOe, whereas Tb3Co7Al2, Dy3Co7Al2 and Dy3Co7.68Si1.32 exhibit best permanent magnet properties in the temperature range of 2–5K with remanent magnetization of 11.95 μB/fu, 12.86 μB/fu and 14.4 μB/fu, respectively and coercive field of 3.0kOe, 1.9kOe and 4.4kOe, respectively.

Structure and magnetism of new rare-earth-free intermetallic compounds: Fe3+xCo3−xTi2 (0 ≤ x ≤ 3)

We report the fabrication of a set of new rare-earth-free magnetic compounds, which form the Fe3Co3Ti2-type hexagonal structure with P-6m2 symmetry. Neutron powder diffraction shows a significant Fe/Co anti-site mixing in the Fe3Co3Ti2 structure, which has a strong effect on the magnetocrystalline anisotropy as revealed by first-principle calculations. Increasing substitution of Fe atoms for Co in the Fe3Co3Ti2 lattice leads to the formation of Fe4Co2Ti2, Fe5CoTi, and Fe6Ti2 with significantly improved permanent-magnet properties. A high magnetic anisotropy (13.0 Mergs/cm3) and saturation magnetic polarization (11.4 kG) are achieved at 10 K by altering the atomic arrangements and decreasing Fe/Co occupancy disorder.

Test Coil과 영구자석의 자기 특성 연구

원자력발전소의 원자로에는 노심 반응 속도를 제어하기 위하여 제어봉구동장치가 사용된다. 한국원자력연구원의 SMART 원자로는 원자로 가동 중 제어봉집합체의 위치를 확인하기 위하여 제어봉구동장치에 영구자석과 리드스위치로 구성되는 위치지시기가 설치된다. 원자로 가동 온도는 최대 <TEX>$350^{\circ}C$</TEX>로 고려되어 설계되며, 영구자석은 원자로 내에 설치된다. 반면에 리드스위치와 전기회로는 원자로 외부에 설치된다. Test coil은 리드스위치의 품질 검증을 위한 장비로서, 코일과 철심으로 구성되어 있다. 본 연구는 리드스위치에 미치는 Test coil과 영구자석의 자기 특성을 비교하고자 수행되었으며, 유한요소 전자기 시뮬레이션을 활용하였다. A CRDM (Control Rod Drive Mechanism) is an electromagnetic device which drives a control rod assembly linearly to regulate the reactivity of a nuclear core. An RPIS (Rod Position Indication System) is used as a position indicator for a control rod assembly of a CRDM of SMART, and an RPIS consists of permanent magnets and reed switches. SMART is designed for the maximum coolant temperature of <TEX>$350^{\circ}C$</TEX>, and the permanent magnets are installed inside of the reactor. The reed switches and electrical circuit are installed outside of the reactor on the other hand. Test coil for a reed switch is test equipment for quality verification of a reed switch, and a test coil consists of a coil and core. In this study, magnetic property of test coil and permanent magnet on a reed switch is compared by using finite element electromagnetic simulation.

Fabrication and mechanical characterization of rare earth permanent magnet SmCo5 films

This study reports mechanical properties of rare earth permanent magnet (REPM) SmCo5 thin films fabricated by RF magnetron sputtering technique. 1 μm thick SmCo5 thin films were grown on Si (100) substrate at room temperature, and later they were annealed at 400 °C. Great care has been taken to decrease O2 in the chamber throughout deposition. Mechanical and Structural properties of SmCo5 thin films were researched using the nanoindentation and in situ scanning probe microscopy (SPM), Grazing Incident X-ray Diffraction (GIXRD) and Scanning Electron Microscopy (SEM) techniques. Nanoindentation-induced plasticity of SmCo5 thin film was characterized by in situ SPM imaging of indented cross-sections. Nanoindentation results show load-displacement curves are continuous and smooth that there is no pile-up and sink-in behavior. Furthermore, both elastic modulus and nanohardness values of REPM SmCo5 exhibit peak load dependence. Nanohardness increases with increasing indentation test load, while the reduced modulus decrease with increasing indentation test load. The obtained values of the intrinsic nanohardness and intrinsic reduced modulus are 3.47 ± 0.07 GPa and 43.09 ± 1.60 GPa, respectively.

Co@CoSb Core–Shell Nanorods: From Chemical Coating at the Nanoscale to Macroscopic Consolidation

Core–shell magnetic anisotropic particles were prepared by reduction of Sb acetate at the surface of cobalt nanorods dispersed in a solution consisting of 1,2 tetradecanediol in oleylamine. X-ray diffraction and local EDS analyses revealed a thin β-CoSb shell with a controlled thickness ranging from 5 to 15 nm that depended on the Sb/Co molar ratio and the reduction temperature. The shell completely coats the rod surface but does not alter the shape anisotropy or the hcp structure of the cobalt cores, and the hard magnetic properties are preserved after coating with a coercivity higher than 3 kOe. Consolidated nanostructured materials that exhibit properties of permanent magnets were prepared by compaction of the core–shell Co@CoSb nanorods. The thin CoSb shell was very efficient for preventing the cobalt anisotropic core from sintering at high temperatures (up to 300 °C) and high pressures (up to 1.5 GPa). These results indicate that the bottom-up approach is very promising for preparation of nanostructu...

Structure and magnetic properties of 300-nm-thick FePt films with Hf underlayer

Structure, microstructure, magnetic properties of 300-nm-thick FePt films with 10-nm-thick Hf underlayer have been studied. The experimental results showed that the very thin Hf underlayer could promote the ordering at reduced temperatures by facilitating the nucleation of the order phase, leading to refined grain size and magnetic domain size. Therefore, the permanent magnetic properties of FePt films were enhanced. (BH)max and Hc of FePt films were greatly enhanced from 5.0–21.0MGOe and 1.4–11.0kOe for single layer to 10.2–23.6MGOe and 4.5–13.2kOe for Hf-underlayered films annealed in Ta region of 400–600°C, respectively. Nevertheless, the severe interdiffusion between the Hf and FePt layers at Ta=800°C resulted in the decreased S, coarsened surface morphology, grain and magnetic domain sizes, and therefore the slightly decreased (BH)max to 18.0MGOe.