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Magnetic micro-actuators and systems (MAGMAS) require tiny permanent magnets with dimensions of hundreds of micrometers. Such magnets need to have the highest possible energy density, which means Nd–Fe–B magnets are the most appropriate type. Most bottom-up fabrication techniques are either too slow or too expensive; top-down techniques involving m...
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... present in alloy 3, with 30.9% Nd. The higher neodymium concentration in the alloys 4 and 5 and the non-equilibrium solidification result in increasingly smaller amounts of f phase and separated solidification of the Nd-rich residual melt. The consequence of this is the presence of primary crystals of neodymium and a binary eutectic (Nd+f). Fig. 2 shows a graph of the effect of the sintering temperature on the intrinsic coercivity of the samples produced in the range 680-960 1C. Each sample was produced from 0.8 g of material and pressed in a die with a diameter of 6 mm. The thicknesses of the samples that fully densified were approximately 5 mm. It is clear that the samples ...
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... coating of the grains and a tendency to form small oxides and defects on the surfaces of the Nd 2 Fe 14 B grains, thus leading to a lower coercivity. The results of the measurements of the same samples' remanent magnetization after magnetizing in a field of 1.8 T are shown in Fig. 3. The curves are similar to the coercivity curves in Fig. 2; this is not surprising as the same inability to densify at low temperatures that reduced the coercivity of the samples from alloys 3 and 4 also results in a decrease in the remanent magnetization of the samples. Fig. 4 shows the microstructures from samples of alloys 3 (Fig. 4a) and 4 (Fig. 4b) that were sintered at 800 ...
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... the basis of the results shown in Figs. 2-4 we chose a sintering temperature of 800 1C and produced samples from alloys 3-5 with thicknesses in the range 100 mm-5 mm. This thickness variation was achieved by altering the amount of powder added to the die between 20 mg and 0.8 g. The results of the measurements of the intrinsic coercivity for different sample thicknesses are ...
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Citations
... Development and size reduction are moving forward in small electronic devices such as MEMS (Micro Electro Mechanical Systems) devices and miniaturized motors comprising of film magnets thicker than several ten microns have been developed. [1][2][3] We have already prepared isotropic rare-earth thick films (≤1200 μm) by using Pulsed Laser Deposition (PLD) method and applied them to small electronic devices. [4][5][6] On the other hand, we have fabricated anisotropic rare-earth film magnets by substrate heating. ...
Anisotropic Nd-Fe-B film magnets are applied to miniaturized electronic devices and MEMS (Micro Electro Mechanical Systems) devices have been prepared by the sputtering method. However, the thickness of each film is mainly less than 20 μm. We have already fabricated anisotropic rare-earth film magnets by pulsed laser deposition (PLD) technique. In this study, an investigation has been carried out on increasing laser beam power for a high deposition rate. Although the thickness of the films increases as laser power increases, it is suggested that the residual magnetic polarization ratio and coercivity values of anisotropic Nd-Fe-B film magnets are not allowed to deteriorate with increasing laser power or deposition rate. These results suggest that we have the facility in obtaining perpendicularly anisotropic Nd-Fe-B thick-film magnets using the PLD method.
... A permanent film magnet is a promising material to develop various industrial and medical fields. [1][2][3] For example, Nd-Fe-B film magnets thicker than 10 µm on metal substrates and metal buffer layers prepared using a sputtering method have been applied to miniaturized electronic devices. 4,5 A friction drive small motor comprising a PLD (Pulsed Laser Deposition)-fabricated isotropic Nd-Fe-B thick film on a Ta substrate was demonstrated by our group. ...
PLD (Pulsed Laser Deposition) method with high laser energy density (LED) above 10 J/cm² followed by a flash annealing enabled us to obtain isotropic nano-composite thick-film magnets with (BH)max ≧ 80 kJ/m³ on polycrystalline Ta substrates. We also have demonstrated that a dispersed structure composed of α-Fe together with Nd2Fe14B phases with the average grain diameter of approximately 20 nm could be formed on the Ta substrates. In this study, we tried to enhance the (BH)max value by controlling the microstructure due to the usage of different metal based substrates with each high melting point such as Ti, Nb, and W. Although it was difficult to vary the microstructure and to improve the magnetic properties of the films deposited on the substrates, we confirmed that isotropic thick-film magnets with (BH)max ≧ 80 kJ/m³ based on the nano-dispersed α-Fe and Nd2Fe14B phases could be obtained on various metal substrates with totally different polycrystalline structure. On the other hand, the use of a glass substrate lead to the deterioration of magnetic properties of a film prepared using the same preparation process.
... [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] In particular, the size reduction in electronic devices comprising rare-earth (RE) thick-film magnets such as Nd-Fe-B and Sm-Co singlelayered films have been reported. [16][17][18][19][20][21][22][23] In our research, an increase in the remanence of an isotropic thick film magnet has been carried out to develop the properties of a miniaturized motor. For example, an approximately 12-µmthick Nd-Fe-B=α-Fe multilayered nanocomposite film with a coercivity of 504 kA=m, a remanence of 1.1 T, and a (BH) max of 112 kJ=m 3 was fabricated by a pulsed laser deposition (PLD) method. ...
An increase in the remanence of an isotropic film magnet is indispensable to improve the properties of miniaturized devices. We, therefore, tried to prepare Pr–Fe–B/α-Fe multilayered nanocomposite thick-film magnets by a pulsed laser deposition (PLD) method. Namely, a rotated target composed of a Pr xFe14B (x = 2.2 or 2.4) target together with an α-Fe segment was ablated. We also took account of a small spot size of the laser beam in order to suppress the emission of droplets (large particles) from each target. An optimization on the area of the α-Fe segment in each Pr xFe14B target was carried out, and the remanence of an annealed film reached approximately 1.1 T. Moreover, a transmission electron microscopy (TEM) observation of the above-mentioned sample revealed that the microstructure varied from a multilayered structure (as-deposited) to a dispersed one through the annealing process. Resultantly, the annealed film had a dispersed nanocomposite structure with good exchange coupling.
... Extensive research efforts are being carried out by several groups of researchers to find new alternatives. Among the recent developments of fabrication methods of permanent magnet are screen printing, electroplating and electrodeposition [82][83][84][85]. Screen printing techniques for depositing and patterning permanent magnet were developed by Lagorce [24]. ...
In the study, laser induced forward transfer (LIFT) of magnetic materials such as α-Fe and Nd-Fe-B was performed to directly deposit on a substrate using YAG laser. Usage of an optical shatter and Galvano scanner enabled us to obtain LIFT-made films with a dotted pattern. Effects of conditions of laser irradiation on the deposited films were investigated. There was a threshold energy density for obtaining α-Fe dot patterns with LIFT. Energy density of laser beam enabled larger size of deposited dot patterns under the same laser spot size. In LIFT-prepared α-Fe films, atmosphere during the deposition strongly did not affect the crystalline structure. On the other hand, the deterioration of coercivity and squareness in LIFT-made Nd-Fe-B films was observed under low vacuum atmosphere of 10 Pa compared with those of LIFT-made ones in the high vacuum of 10-4 Pa. It was also confirmed that Nd-Fe-B films with coercivity of 290 kA/m on a paper could be deposited via a LIFT technique.
Ce travail de thèse est consacré au développement d'un capteur acoustique miniature à transduction capacitive destiné à être intégré dans un système RFID afin de dépasser certaines des limitations actuelles de ce dernier. La configuration originale du capteur acoustique étudié lui offre les avantages d'avoir une bonne performance tout en gardant une forme simple qui peut être aisément réalisée avec les techniques MEMS pour une production à grande échelle. Ce transducteur est constitué d'une membrane circulaire ou carrée et une électrode arrière centrée, de même forme mais de dimensions plus petites, séparées par une très fine couche de fluide, ainsi qu'une petite cavité située à la périphérie de l'électrode, de dimensions extérieures très proches de celles de la membrane. Le comportement de ce capteur est analysé en détail. Cette étude se base sur deux approches mathématiques originales (analytique et numérique), dont les résultats convergent malgré un niveau différent des hypothèses-simplificatrices sur lesquelles reposent ces deux modèles.Finalement, une méthode de réalisation du transducteur en technologie hybride, qui associe le procédé MEMS avec les techniques classiques des circuits imprimé, est présentée. Le prototype développé est aussi caractérisé expérimentalement et les résultats obtenus correspondent bien aux caractéristiques fournies par les modèles théoriques.
In order to deposit isotropic Nd-Fe-B film magnets on metal substrates, a laser beam with an energy density of approximately 3 J/cm² was defocused on the surface of Nd-Fe-B sintered targets with three densities of 5.69, 6.14, and 6.64 g/cm³, respectively. The different Nd content (Nd/(Nd + Fe)) between each film and the corresponding targets decreased as the density of the targets increased. We have reported that the deposition using a Nd-Fe-B alloy target under the same laser energy density and T-S distance enabled us to obtain the good transfer of composition from an alloy target to a film. It was clarified that the similar result could be obtained in the use of a sintered target with the density of 6.64 g/cm³. Comparison of magnetic properties, normalized demagnetization curves, and microstructure between the films prepared using a sintered target (6.64 g/cm³) and a Nd-Fe-B alloy target, respectively, was carried out. The values of coercivity and (BH)max of the samples prepared by the sintered target were higher than those of the films prepared using the alloy one. Moreover, the use of a Nd-Fe-B sintered target enabled us to improve the reproducibility of squareness in demagnetization curves. It is considered that the results of comparison are attributed to the different microstructure of the films such as the precipitation due to uneven distribution of α-Fe and Nd elements. We also suppose that the formation of microstructure in each film originates from the microstructure of the corresponding targets.
We have already prepared a thin permanent magnet with the thickness of sub-millimeter by obtaining magnet powders using a pulsed laser deposition (PLD) method. In the article, the PLD followed by a flash annealing enabled us to deposit isotropic Pr–Fe–B magnet powders with coercivity
kA/m on a stainless thin shaft applicable to a miniaturized motor. Observation on the surface of Pr–Fe–B magnets and evaluation on the mechanical behavior were carried out. Since the surface of a Pr–Fe–B magnet was coated by a Pr oxide through an annealing process, their magnetic properties did not degrade after one year. We also confirmed that the Pr–Fe–B magnet has the possibility to be applied to a micro-magnetization process. It was clarified that the powder technology using the PLD is useful to propose a thin magnet applicable to a next-generation small motor.
