Papers by Keyword: Coercivity

Abstract: NdFeB magnets were first developed in 1984 and are the most powerful permanent magnets that may possess energy products up to 60 MGOe. However, their working temperature and corrosion resistance are lower as compared to that of Alnico and SmCo magnets. Demand of NdFeB magnets recently has increased due to rapid growth of electrical vehicles. In this research work, NdFeB magnets developed through powder metallurgical technique are investigated for thermal effect on magnetic characteristics. The effect of increase in temperature on remanence, coercivity and energy product were measured using pulsed field magnetizer. Samples for testing were prepared from sintered bricks using wire cut machine. Demagnetization curves for the samples were measured at temperatures in the range of 20-110°C, and the results were analyzed. Decline in magnetic characteristics with temperatures is noted. Performance of the magnets with increase in temperature is essential to be analyzed specially for their use in high-speed motors.

Abstract: We developed a new 1-12-type magnetic material of (Sm,Zr)(Fe,Co)_11.3Ti_0.7 composition that exhibits magnetic properties superior to Nd-Fe-B magnets. In the new 1-12 magnets, the amorphous alloys of above composition show a change in XRD pattern with increasing of heat treatment temperature from a single 1-9 phase to 1-9 and 1-12 mixed phases, and finally to a single 1-12 phase, and the magnetic properties also change accordingly. In this study, we established a method for calculating the formation ratio of the 1-12 phase in the samples from the peak shift of the diffraction peaks of the 1-12 phase base on the peaks of the 1-9 phase. As a result, it was revealed that the formation ratio of the 1-12 phase in the samples, whose XRD pattern of 1-9 and 1-12 mixed phase, has a wide distribution, ranging from about 20 to 80 %. With the development of the phase transition from 1-9 to 1-12 phases, the lattice constant a of 1-12 phase increases, and inversely the lattice constant c of 1-12 phase decreases. Furthermore, it was revealed that the formation ratio of the 1-12 phase was about 83 % for the sample indicating the maximum coercivity H_c = 5.46 kOe.

Abstract: In this study, an increase in the reflection loss (RL) value for SrFe_(11.9-x)In_0.1Sn_x/2Zn_x/2O₁₉ samples (x = 0; 0.10; 0.35 and 0.50) is reported. The X-ray diffraction (XRD) pattern of all samples confirmed that the SrFe_(11.9-x)In_0.1Sn_x/2Zn_x/2O₁₉ samples (x = 0, 0.10, 0.35, and 0.50) posses polycrystalline with single phase. We have demonstrated that co-substitution of Zn²⁺ and Sn⁴⁺ ions with a fraction of x = 0.10 reduced the coercivity of the pure nano strontium hexaferrite (SHF) from 346.80 kA/m to 50.34 kA/m. The substitution of Fe³⁺ ion by Sn²⁺ and Zn⁴⁺ affect the coercivity decreased significantly. Meanwhile, the saturation magnetization and remanence slightly decreases. Hence, the decreasing of coercivity cause the reflection loss (RL) increase from -16.43 dB to -25.62 dB. We believed the RL value can be increased efficiently by reducing the coercivity of the sample obtained by co-substitution of Zn²⁺ and Sn⁴⁺ ions to Fe³⁺ in the main phase of SrFe_11.9In_0.1O₁₉.

Abstract: In this paper, a theoretical model based on multi-gene genetic programming (MGGP) approach has been applied to predict the structural and magnetic properties in nanocrystalline Fe–Ni powders prepared by mechanical alloying (MA) using a planetary ball mill. The MGGP model was used to correlate the input parameters (milling speed, chemical composition, and milling time), to output parameters (crystallite size and coercivity) of nanocrystalline Fe–Ni powders. The model obtained was tested with additional data to demonstrate its performance and prediction ability. The MGGP model is a robust and efficient method to find an accurate mathematical relationship between input and output data. A sensitivity analysis study was applied to determine the most influential milling parameters on the crystallite size and coercivity.

Abstract: The microstructure and magnetization of SmCo₅ micro-particles may be used as feedstock for 3D printing to make miniature strong magnets. Thus, the magnetic response and microstructures of commercially available SmCo₅ micro-particles were studied under various heat treatments using a high wattage laser. The magnetization of laser heat treated powders at 50-watt showed an increase in magnetization, while the 75-watt melt showed a little to no change. Unfortunately, the coercivity of both laser heat treated samples decreased significantly. Oxidation during the heat treatment is suspected to result in low coercivity. Purging with argon-gas prior to laser heating showed improved coercivity. To further minimize the oxidation problem a set of SmCo₅ powder was reduced prior to laser heat treatment using a constant flow of hydrogen gas while being heated at various temperatures from 100 oC to 400 oC for a period of ~4 hours. The results show that the magnetization generally increases with the temperature, while the coercivity decreases significantly. Another set of SmCo₅ was annealed in a vacuum furnace for one hour at temperatures between 200 oC and 400 oC in order to confirm that no hydride phases were formed during reduction. The magnetization and coercivity showed similar variations with annealing temperature to those for the reduced powders confirming that these variations may be due to change in crystal structure rather than formation of hydrides. X-ray Diffraction (XRD) studies were performed to identify the changes in crystal phases.

Abstract: The purpose of this study is to obtain a permanent magnet end-product from NdFeB and NdFeB / Co-Al composite material from SPS sintering which has high density with small grain size and strong corrosion resistance. NdFeB powder and NdFeB/Co-Al composites (0.2 and 0.5weight%) of several micron-sized particles resulting from the milling process have been successfully sintered with a temperature parameter of 800°C for 10 minutes and a pressure of 50MPa in dies with a diameter of 20 mm in a vacuum chamber. Optical micrographs show that the grains are uniformly and smoothly distributed throughout the surface. This is showing the types of grain distributions which has good mechanical properties. The X-ray analysis result shows the phase analysis confirms the presence of such main PM phases as Nd, Fe and B. From SEM observation, the particles have irregular shapes and a large particle size distribution. The density value of the sample is in the range of 7.1 - 7.3. From the density measurement it is also known that the sintering sample with SPS has a high-density level which is close to 100%, so it can be said that it has formed fully dense.

Abstract: Permanent Magnets made in the form of hybrid bonded BaFe₁₂O₁₉ / NdFeB and with binder of Poli Vynil Alcohol (PVA) as much as 3% of the total mass in each sample. The weight ratio hybride system BaFe₁₂O₁₉ : NdFeB is 0 % BaFe₁₂O₁₉ : 100 % NdFeB ; 50% BaFe₁₂O₁₉ : 50 % NdFeB and 70% BaFe₁₂O₁₉ : 30 % NdFeB. The material preparation process was begun from mixing of raw materials using HEM for 15 minutes, then added 3% wt. of PVA. The mixed powder was formed a pellet using a hydraulic press with a force of 4 tons for 1 minute, then heated with an vacuum oven at a temperature of 110 ° C for 1 hour and the last step was magnetization using impulse magnetizer. The characterization of pellet sample was done namely measurement of bulk density, flux magnetic and hysteresis loop using VSM and then measurement of corrosion resistance of hybride bonded magnet. The characterization results show that bulk density value of sample hybride 50% BaFe₁₂O₁₉ – 50 % NdFeB is more larger than sample hybride 70% BaFe₁₂O₁₉ – 30 % NdFeB , and The highest coercivity and remanence values ​​of 3900 Oe and 2500 Gauss respectively were achieved in samples with a composition of 50% Ba-ferrite - 50% NdFeB. The hybride bonded magnet Ba-ferrite/NdFeB has more corrosion resistance than bonded magnet 100 % NdFeB.

Abstract: A bonded permanent magnet of Barium hexa Ferrite has been made using powder BaFe₁₂O₁₉ (commercial ferrite) and a polymer of bakelite powder as binder. The composition of bakelite was varried 5% wt. The preparation of sample was begun with mass weighing for each material, then mixed together using ball mill for 1, 6 and 12 hours and using aquades as milling media. The mixed powder is dried in an oven at 110 °C for 4 hours, then the particle size distribution was measured. After that, the dried sample powder was pressed to form a pellet at pressure 40 MPa and temperature about 160 °C for 20 minutes. The characterization of sample pellet was done such as measurement of bulk density, hardness , magnetic properties using VSM and anylisis of microstructure using SEM. The results of the characterization show that the density and magnetic properties tend to increase with increasing of milling time, where the highest density, hardness and highest magnetic properties are achieved at sample with milling time for 12 hours. The value of magnetic properties at this condition are flux magnetic of 530 Gauss, remenance of 3100 Gauss, coercivity of 1,10 kOe.

Abstract: Neodymium substituted yttrium iron garnet (YIG) nanoparticles with compositional variation of Nd_xY_3−xFe₅O₁₂ where x = 0.0, 0.2, 0.5 and 0.8 was prepared by mechanochemicals method using high energy milling (HEM). The characterization was done using X-rays diffractometer (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA). It was found that the mechanical milling followed by sintering promotes the complete structural formation of the yttrium iron garnet (YIG) structure. The XRD patterns confirm the complete introduction of Nd³⁺ ion into the YIG with an addition of Nd doping concentration. nanocrystalline particles with high purity and sizes ranging from 0.12μm to 0.16μm were obtained. The magnetization value, M_s from all Nd-doped samples were obtained in the range between 34 to 37emu.g^-1. The magnetic coercivity (H_c) was achieved of 0.012kOe (12Oe) for the non-doped sample (YNd-0) and then increase with the addition of neodymium concentration. The increase in H_c for all the sample series can be attributed to an enhancement of the magnetocrystalline anisotropy with anisotropic Fe²⁺. The variation of the reflection loss (RL) versus frequency was observed in Nd doped YIG, Y_1-xNd_xFe₅O₁₂ with x = 0.0 – 0.8 in the frequency range of 7 –12 GHz. The optimum reflection loss (RL) was found to be 8.66(-dB) at 9.5GHz in Y_2.2Nd_0.8Fe₅O₁₂ (YNd-08) for x = 0.8.

Abstract: Aiming at the evaluation of creep damage at elevated temperature of ferromagnetic materials in engineering application, the hysteresis loop measurement technology was adopted to study the creep damage behaviour of 1Cr5Mo steel. The creep testing at 600°C/90MPa of 1Cr5Mo steel were carried out to prepare specimens with various degrees of creep damage. The variation of magnetic parameter including coercivity (H_C) and remanence (Br) with creep damage was analyzed. The microstructure evolution of 1Cr5Mo steel with different degrees of creep damage was observed by optical microscope. The results show that the coercivity and remanence show certain regularity with creep damage at elevated temperature. Moreover, the regularity is repeatable which indicates that the measurement technology based on magnetic parameters can be used for the evaluation of high temperature creep damage.