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  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
  • H01F41/0273—Imparting anisotropy
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/005—Impregnating or encapsulating
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  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/32—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying conductive, insulating or magnetic material on a magnetic film, specially adapted for a thin magnetic film
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
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  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/24—After-treatment of workpieces or articles
  • B22F2003/248—Thermal after-treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
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  • C22C2202/00—Physical properties
  • C22C2202/02—Magnetic
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  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
  • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
  • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
  • H01F1/0576—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together pressed, e.g. hot working
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/047—Alloys characterised by their composition
  • H01F1/053—Alloys characterised by their composition containing rare earth metals
  • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
  • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
  • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
  • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
  • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
• • H—ELECTRICITY
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  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F10/00—Thin magnetic films, e.g. of one-domain structure
  • H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
  • H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
  • H01F10/12—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys
  • H01F10/126—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition being metals or alloys containing rare earth metals

Definitions

• the present invention relates to a production method of a rare earth magnet, which is usually represented by a neodymium magnet and neodymium magnet films which apply to MEMS (Micro Electro Mechanical Systems). More
• the present invention relates to a
• a rare earth magnet which is represented by a neodymium magnet (Nd 2 FeiB) and neodymium magnet films which apply to MEMS (Micro Electro Mechanical Systems), is used as a very strong permanent magnet having a high magnetic flux density for various applications.
• the crystal grain size is being reduced to the nano-scale (several tens to several hundreds of nm) .
• the enhancement of the magnetic coercive force by a heat treatment is desirable. Accordingly, it is needed to establish an optimal heat treatment method.
• Patent Document 1 Japanese Unexamined Patent
• Patent Document 2 Japanese Unexamined Patent
• An object of the present invention is to provide a production method of a rare earth magnet, which is usually represented by a neodymium magnet (Nd 2 Fei 4 B) and neodymium magnet films which apply to MEMS (Micro Electro Mechanical Systems) , wherein a heat treatment method capable of enhancing the magnetic characteristics, particularly the magnetic coercive force is used.
• a rare earth magnet which is usually represented by a neodymium magnet (Nd 2 Fei 4 B) and neodymium magnet films which apply to MEMS (Micro Electro Mechanical Systems)
• MEMS Micro Electro Mechanical Systems
• the present invention provides a method for producing a rare earth magnet, comprising:
• the present invention provides a method for producing a rare earth magnet in the form of a bulk, comprising:
• quenching a molten metal having a rare earth magnet composition to form quenched flakes having a
• an element which is capable of lowering the temperature at which the grain boundary phase can be diffused or fluidized, is added to the rare earth magnet composition.
• the rare earth magnet composition is Ndi 5 Fe 77 B 7 Ga
• the main phase of the rare earth magnet is Nd 2 Fei 4 B
• the orientation treatment is a hot working.
• a heat treatment is applied with pressurization at a temperature sufficiently high to enable diffusion or fluidization of a grain boundary phase and, at the same time, low enough to prevent coarsening of the crystal grain size.
• a grain boundary phase unevenly distributed in the space formed among crystal grains and at triple points, that is, at a portion where three or more crystal grains are joined, is re-distributed to the entire grain boundary in order to create the state wherein a nano-size main phase crystal grain is covered with a grain boundary phase to prevent the exchange coupling between main phase grains and thereby to enhance the magnetic coercive force .
• FIG. 1 schematically shows the method for producing quenched flakes by a single roll method.
• Fig. 2 schematically shows the method for separating the quenched flakes into amorphous flakes and crystalline flakes.
• FIG. 3 schematically shows a comparison of a morphology change (movement) of a grain boundary phase due to heat treatment, with respect to (A) a conventional sintered magnet and (B) a nanocrystalline magnet of the present invention.
• FIG. 4 shows a comparison of a
• Fig. 5 shows a change in magnetic
• Fig. 6 shows a magnetic coercive force before and after heat treatment of various times of a rare earth magnet having a nanocrystalline structure (Reference Example 2) .
• Fig. 7 shows a magnetic coercive force before and after heat treatment at various heating rates of a rare earth magnet having a nanocrystalline structure (Reference Example 3) .
• Fig. 8 shows a TEM image of a
• Fig. 9 shows an HAADF image of a
• nanocrystal structure and an EDX ray analysis chart before and after heat treatment (Reference Example 4).
• the arrow indicates the portion analyzed by EDX ray analysis.
• Fig. 10 shows magnetization curves
• Fig. 11 shows the relationship between the magnetic coercive force before heat treatment or after heat treatment (pressure: 0 MPa, 10 MPa, or 40 Pa) , and the pressure at the heat treatment.
• Fig. 12 shows the cross-sectional SEM images and coercivity values of the NdFeB layers.
• Fig. 13 shows the measurement of
• Fig. 14 shows the cross-sectional SEM images of the NdFeB and Ta capping layers.
• Fig. 15 shows the coercivity measurements of the NdFeB layers.
• the magnetic coercive force can be enhanced, while preventing
• a rare earth magnet which has a rare earth magnet composition configured to have a nanocrystalline structure, and has been subjected to an orientation treatment.
• R 1 one or more kinds of rare earth elements including Y,
• M 1 at least one of Ga, Zn, Si, Al, Nb, Zr, Ni, Cu Cr, Hf, Mo, P, C, Mg and V,
• R 1 v Fe w Co x B y M 1 z the amount v of R 1 (one or more kinds of rare earth elements including Y) is 13 ⁇ v ⁇ 17 and the amount y of B is 5 ⁇ y ⁇ 16.
• compositional formula and composed of a main phase ( (R 2 R 3 ) 2 (FeCo) i 4 B) and grain boundary phases
• R 2 one or more kinds of rare earth elements including Y (excluding Dy and Tb) ,
• R 3 one or more kinds of heavy rare earth elements consisting of Dy and Tb
• M 2 at least one of Ga, Zn, Si, Al, Nb, Zr, Ni, Cu Cr, Hf, Mo, P, C, Mg, Hg, Ag and Au,
• composition is quenched to form flakes having a structure composed of nanocrystals (nanocrystalline structure) .
• the nanocrystalline structure is a polycrystalline structure where the crystal grain is of nano size.
• the nano size is a size in the range 10 to 300 nm.
• the quenching rate is in the range suitable for allowing the solidified structure to become a
• the quenching rate is less than this range, the solidified structure becomes a coarse crystal structure, and thereby a nanocrystalline structure is not obtained. If the quenching rate is more than this range, the solidified structure is amorphous, and thereby a nanocrystalline structure is not obtained.
• the method for quenching solidification need not be particularly limited, but this is preferably performed by using a single-roll furnace shown in Fig. 1.
• a molten alloy is ejected out from a nozzle (3) on the outer circumferential surface of a single roll (2) rotating in the direction of the arrow (1), the molten alloy is quenched and solidified, and thereby becomes flakes (4).
• quenched flakes are formed by solidification due to one-direction
• the quenching rate tends to fluctuate to a higher rate than
• quenched flakes have either a nanocrystalline structure or an amorphous structure.
• quenched flakes of nanocrystalline structure needs to be selected from the mixture of the quenched flakes having different
• the quenched flakes are separated into crystalline flakes and amorphous flakes by using a low magnetization magnet. More
• amorphous quenched flakes are magnetized by the magnet and kept from falling (2), whereas crystalline quenched flakes are not magnetized by the magnet and are allowed to fall (3) .
• the produced (if desired, separated) quenched flakes of nanocrystalline structure are sintered.
• the sintering need not be particularly limited in its method, but must be performed at a low temperature in as short a time as possible so as to prevent coarsening of the
• the heating rate to the sintering temperature is also preferably high.
• sintering by electric current (resistance) heating with pressurization for example, sintering commonly referred to as “Spark Plasma Sintering (SPS) " is preferred. Under pressurization, more electric current can pass so that the sintering temperature can be lowered, and the temperature can be raised to the sintering temperature in a short time.
• SPS Spark Plasma Sintering
• sintering need not be limited to SPS sintering, and may also be performed by using a hot press .
• thermoforming machine As a type of hot press, it is also possible to use a normal press molding machine or the like in combination with high frequency heating and heating with an attached heater. In high frequency heating, the work piece is directly heated by using an insulating die/punch tool, or the work piece is indirectly heated by the heated
• the die/punch tool In heating with an attached heater, the die/punch tool is heated with a cartridge heater, a band heater or the like.
• the obtained sintered body is subjected to an orientation treatment.
• a representative method for the orientation treatment is a hot working.
• severe plastic deformation where the working degree, i.e., the decrease in thickness of the sintered body, is
• the crystal grain itself and/or the crystal direction in the crystal grain are rotated in association with slide deformation, and thereby the sintered body is oriented (development of texture) in the easy direction of
• the sintered body has a nanocrystalline structure, the crystal grain itself and/or the crystal direction in the crystal grain are easily rotated and thereby the orientation is
• the method for the orientation treatment is not limited to a hot working, and may be sufficient if the crystal grains can be oriented while maintaining the nanocrystal structure.
• anisotropic powder e.g., Hydrogenation-
• HDDR Disproportionation-Desorption-Recombination
• a heat treatment with pressurization which is the characteristic feature of the present invention, is applied.
• the heat treatment decrease in
• thickness of the orientation-treated sintered body is not substantial, for example the decrease in thickness is 5% or less, 3% or less, or 1% or less.
• the heat treatment with pressurization is performed so as to cause a grain boundary phase, which is unevenly distributed mainly in the triple points of the grain boundaries, to diffuse or fluidize along the entire grain boundary.
• the heating is associated with pressurization, so that diffusion or fluidization of the grain boundary phase can be accelerated, while suppressing the grain growth incurred by the heat treatment. Also, due to pressurization associated with the heating, the grain boundary phase, which is unevenly distributed mainly in the triple points among crystal grains of the main phase, can be extruded from the triple points, and thereby diffusion or fluidization of the grain boundary phase can be accelerated.
• a grain boundary phase between adjacent main phases does not exist (or does not exist in a sufficient amount) in some place.
• exchange coupling across a plurality of main phase grains increases the effective main phase size, as a result, the magnetic coercive force is low.
• the exchange coupling between adjacent main phases is prevented by the grain boundary phase, and thereby the effective main phase size remains small, so that a high magnetic coercive force can be obtained.
• the pressurization is a temperature sufficiently high to enable diffusion or fluidization of the grain boundary phase, and at the same time, low enough to prevent coarsening of the crystal grains.
• the melting point of the grain boundary phase is the index of the temperature enabling diffusion or fluidization of a grain boundary phase.
• the lower limit of the heat treatment temperature is in the vicinity of the melting point of the grain boundary phase, for example Nd-Cu phase
• the upper limit of the heat treatment temperature is a temperature allowing no coarsening of the main phase, for example Nd2Fei 4 B phase, that is, for example, 700°C.
• the melting point of the grain boundary phase can be lowered by the addition of an additive element. More specifically, for example, in the case of a neodymium magnet, the heat treatment temperature can be selected from the range of 450 to 700°C.
• the pressure applied to the sintered body during the heat treatment with pressurization can be 1 MPa or more, 5 MPa or more, 10 MPa or more, or 40 MPa or more, and 100 MPa or less, 150 MPa or less, 200 MPa or less, or 300 MPa or less.
• the time of heat treatment with pressurization can be 1 minute or more, 3 minutes or more, 5 minutes or more, or 10 minutes or more, and 30 minutes or less, 1 hour or less, 3 hours or less, or 5 hours or less.
• the effect on the magnetic coercive force can be obtained even when this holding time is a relatively short time, for example, about 5 minutes.
• Fig. 3 shows (1) a photograph of the structure before heat treatment, (2) a schematic image of the structure before heat treatment and (3) a schematic image of the structure after heat treatment, with respect to (A) a conventional sintered magnet and (B) a
• nanocrystalline magnet of the present invention In the schematic images (2) and (3), the shaded crystal grains and the gray crystal grains are reversed in magnetization direction .
• the grain boundary phase is unevenly distributed at triple points of the crystal grain boundary, and a grain boundary phase does not exist or exists in a very small amount in the grain boundary other than at the triple points. Accordingly, the grain boundary does not act as a barrier against the movement of magnetic domain walls, and since the magnetic domain walls move to the adjacent crystal grains across the crystal grain boundary, a high magnetic coercive force is not obtained.
• the grain boundary diffuses or fluidizes from the triple points, and sufficiently permeates the grain boundary other than the triple points to cover the entire crystal grain.
• the grain boundary phase exists in a sufficient amount in the grain boundary to prevent the movement of magnetic domain walls, and thereby the magnetic coercive force is
• the grain boundary is unevenly distributed at the triple points of the crystal gain boundary, and a grain boundary phase does not exist or exists in a very small amount in the grain boundary other than the triplet point.
• the grain boundary does not act as a barrier against exchange coupling between adjacent crystal grains, and since adjacent crystal grains interact together through exchange coupling (2') to allow
• the grain boundary phase diffuses or fluidizes from the triple points, and sufficiently permeates the grain boundary other than the triple points to cover the entire crystal grain.
• the grain boundary phase exists in a sufficient amount in the grain boundary to prevent exchange coupling between adjacent crystal grains (3 1 ), and therefore the magnetic coercive force is enhanced. Furthermore, due to a nanocrystalline
• the grain boundary phase diffused or fluidized from the triple pints to cover the crystal grains in a very short time, so that the heat treatment time can be greatly reduced.
• an element capable of lowering the melting point of the grain boundary phase is added to the rare earth magnet composition.
• the rare earth magnet composition is represented by the formula
• an Nd-rich grain boundary phase is formed, for example when the rare earth magnet composition is represented by the formula Ndi 5 Fe 77 B 7 Ga and the rare earth magnet is composed of a main phase Nd2Fei 4 B and an Nd-rich grain boundary phase, an element capable of alloying with Nd and thereby lowering the temperature at which the grain boundary phase can be diffused or fluidized, is added to the rare earth magnet composition above in an amount sufficiently large to bring about the effect of lowering the
• Ga has been conventionally used as an element having an effect of decreasing the crystal grain size, particularly for suppressing the crystal grain growth during hot working.
• Examples of the elements capable of alloying with Nd and thereby lowering the temperature at which the grain boundary phase can be diffused or fluidized include Al,
• the amount of such an additive element to be added can be from 0.05 to 0.5 atm%, preferably from 0.05 to 0.2 atm%.
• a film having a rare earth magnet composition is deposited on a substrate by any kind of process such a chemical vapor deposition (CVD) and physical vapor deposition (PVD) .
• the thickness of the film can be 0.50 ⁇ or more, 1.00 ⁇ or more, 2.00 ⁇ or more, or 3.00 ⁇ or more. Further, the thickness of the film can be 1000 ⁇ or less, 100 ⁇ or less, 50 ⁇ or less, or 10 ⁇ or less .
• a heat treatment with pressurization which is the characteristic feature of the present invention, is applied.
• a difference in thermal expansion coefficients of the substrate and the film deposited thereon can be used.
• the pressure applied to the film during the heat treatment with pressurization can be 1 MPa or more, 5 MPa or more, 10 MPa or more, 50 MPa or more, or 100 MPa or more, and 300 MPa or less, 400 MPa or less, or 500 MPa or less.
• the time of heat treatment with pressurization can be 1 minute or more, 3 minutes or more, 5 minutes or more, or 10 minutes or more, and 30 minutes or less, 1 hour or less, 3 hours or less, or 5 hours or less.
• the effect on the magnetic coercive force can be obtained even when this holding time is a relatively short time, for example, about 5 minutes.
• the description for the first embodiment can be referred.
• a nanocrystalline rare earth magnet of the present invention A nanocrystalline rare earth magnet of the present invention
• composition Ndi 5 Fe 77 B 7 Gai and a nanocrystalline rare earth magnet of the composition comprising Al and Cu, i.e.
• Ndi5Fe 77 B 6 . 8 Gao.5Alo.5Cuo.2 / were produced.
• the finally obtained structure is a nanocrystalline structure
• Nd 2 Fei 4 Bi phase composed of a main phase: Nd 2 Fei 4 Bi phase, and a grain boundary phase: Nd-rich phase (Nd or Nd oxide) or NdiFe 4 B4 phase.
• Ga is enriched in the grain boundary phase to prevent the movement of grain boundaries and suppress the coarsening of crystal grains.
• Both Al and Cu alloy with Nd in the grain boundary phase and enables diffusion or fluidization of the grain boundary phase.
• Each raw material of Nd, Fe, B, Ga, Al and Cu was weighed to a predetermined amount so as to give the two above-described compositions, and melted in an arc melting furnace to produce an alloy ingot.
• the alloy ingot was melted in a radio-frequency furnace, and the obtained molten alloy was quenched by ejecting it out on the roll surface of a copper-made single roll as shown in Fig. 1.
• the conditions employed are as follows.
• Nozzle diameter 0.6 mm
• the quenched flakes (4) were separated into nanocrystalline flakes and amorphous flakes by using a low magnetization magnet.
• amorphous quenched flakes were made of a soft magnetic material, and therefore easily magnetized by the magnet and kept from falling (2), whereas nanocrystalline quenched flakes were made of a hard magnetic material, and therefore not magnetized by the magnet and thus allowed to fall (3) . Only fallen nanocrystalline
• quenched flakes were collected, and subjected to the following treatment.
• the obtained nanocrystalline quenched flakes were sintered by SPS under the following conditions.
• a low melting point phase was formed on one surface of the quenched flakes by the use of the single roll method, and this also contributes to the low- temperature sintering.
• the melting point of the main phase Nd 2 Fei 4 Bi is 1,150°C
• the melting point of the low melting point phase is, for example,
• the above- described low-temperature sintering at 570°C could be achieved by the combination of the effect of lowering the sintering temperature due to the pressurization of the pressure sintering (surface pressure: 100 MPa) , and the effect of lowering the sintering temperature due to the low melting point phase formed on one surface of the quenched flake.
• Atmosphere vacuum of 10 ⁇ 2 Pa
• the obtained severely plastically deformed material was cut into a 2-mm square shape, and subjected to a heat treatment under the following conditions.
• Holding temperature varied in the range of 300 to 700°C
• Heating rate from room temperature to holding temperature 120°C/min (constant)
• Cooling Specifically, the sample was taken out from the heat treatment furnace in a glove box, and allowed to cool to the room temperature state in the glove box . )
• Each of the samples comprising and not comprising Al and Cu was measured by VSM for magnetic characteristics, before and after heat treatment.
• Fig. 4 shows magnetization curves (demagnetization curves) of a rare earth magnet comprising Al and Cu as a typical example before and after heat treatment at 600°C. It is seen that the magnetic coercive force was enhanced by 2 kOe from 16.6 kOe to 18.6 kOe by the heat treatment.
• the relationship between the change (%) of magnetic coercive force based on that before heat treatment, and the heat treatment temperature is shown in Fig. 5 and Table 1.
• the increase of magnetic coercive force by the heat treatment is seen in the heat treatment temperature range of 600 to 680°C.
• the ratio of increase is about 3% (about 0.5 kOe) at a maximum.
• the increase of magnetic coercive force by the heat treatment is seen over a wide heat treatment temperature range of 450 to 700°C.
• the ratio of increase is about 13% at a maximum, and constitutes a significant rise.
• the temperature range wherein the magnetic coercive force is increased by the heat treatment appears to be expanded, and the increment of the magnetic coercive force is also enhanced.
• the eutectic temperature of Nd-Al or Nd-Cu is significantly lower than the melting point of Nd. That is, it is considered that diffusion or fluidization of the grain boundary phase is greatly accelerated by the introduction of Al and Cu into the grain boundary phase, and thereby the grain boundary phase is redistributed to the crystal grain boundary of the main phase Nd 2 FeiB, and prevents the exchange coupling between main phase grains, as a result, the magnetic coercive force is increased.
• Heating rate from room temperature to holding temperature 120°C/min (constant) Holding time: varied in the range of 10 seconds to 30 minutes
• the relationship between the magnetic coercive force after heat treatment and the holding time (600°Cxt) is shown in Fig. 6 and Table 2.
• the magnetic coercive force before heat treatment is also shown. It is seen that the magnetic coercive force is enhanced by the heat treatment even for a short time of 10 seconds, and moreover, this effect is scarcely changed by the heat treatment up to 30 minutes.
• the holding time in the heat treatment must be from 1 to
• the nanocrystalline magnet above has a crystal grain size of typically around 100 nm (0.1 um) , and the surface area of the crystal grain is smaller by about 2 orders of
• the time required for the grain boundary phase to be diffused or fluidized ' by the heat treatment and cover the crystal grain is considered to be greatly reduced.
• Heating rate from room temperature upto holding temperature varied in the range of 5 to 600°C/min
• the magnetic coercive force before heat treatment is also shown.
• the effect of enhancing the magnetic coercive force by the heat treatment shows almost no dependency on the temperature rising rate.
• the temperature rising rate is low, this has a risk of coarsening the structure and is considered as disadvantageous.
• a higher heating rate is preferred from the standpoint of suppressing the coarsening of the structure, and at the same time, reducing the processing time.
• the TEM sample was prepared by processing with FIB (focused ion beam) and ion-milling to be a thin flake.
• Heating rate from room temperature upto holding temperature 120°C/min
• Fig. 8 shows the TEM images before and after heat treatment. Before heat treatment, in many portions, adjacent main phase grains are in direct contact with each other at the grain boundary without intervention of a grain boundary phase. In contrast, after heat
• the structure was changed such that, in many portions, an amorphous grain boundary phase is present at the grain boundary.
• the crystal grain size of the main phase was scarcely changed before and after the heat treatment, and was essentially constant.
• Fig. 9 shows the HAADF image and the EDX ray
• composition of the grain boundary phase after heat treatment is not Nd-rich as compared with the composition before heat treatment.
• a rare earth magnet having an improved magnetic coercive force as compared with the case of performing heat treatment with no pressurization is obtained.
• a nanocrystalline rare earth magnet of the present invention A nanocrystalline rare earth magnet of the present invention
• composition Ndi6Fe7-7.4B5.4Gao.5 lo.5Cuo.2 was produced.
• the finally obtained structure is a nanocrystalline structure composed of a main phase: Nd 2 Fei4Bi phase, and a grain boundary phase: Nd-rich phase (Nd or Nd oxide) or NdiFe 4 B 4 phase.
• Ga is enriched in the grain boundary phase to block the movement of grain boundaries, and suppress the coarsening of crystal grains.
• the alloy ingot was melted in a radio-frequency furnace, and the obtained molten alloy was quenched by ejecting it out on the roll surface of a copper-made single roll, as shown in Fig. 1.
• the conditions employed are as follows.
• Nozzle diameter 0.6 mm
• the quenched flakes (4) were separated into nanocrystalline flakes and amorphous flakes by using a low magnetization magnet. More specifically, out of quenched flakes (4) of (1), amorphous quenched flakes were made of a soft magnetic material, and therefore magnetized by the magnet and kept from falling (2) , whereas nanocrystalline quenched flakes were made of a hard magnetic material, and therefore not magnetized by the magnet and thus allowed to fall (3) . Only fallen nanocrystalline quenched flakes were
• Atmosphere vacuum of 10 ⁇ 2 Pa
• a low melting point phase was formed on one surface of the quenched flake by the use of the single roll method, and this also contributes to the low- temperature sintering.
• the melting point of the main phase Nd2Fei 4 Bi is 1,150°C
• the melting point of the low melting point phase is, for example,
• the above-described low- temperature sintering at 570°C could be achieved by the combination of the effect of lowering the sintering temperature due to the pressurization of the pressure sintering (surface pressure: 100 MPa), and the effect of lowering the sintering temperature due to the low melting point phase formed on one surface of the quenched flake.
• Heating rate from room temperature upto holding temperature 120°C/min (constant)
• Fig. 10 shows magnetization curves (demagnetization curves) of samples before heat treatment, after heat treatment with no pressurization, and after heat
• Fig. 11 shows the relationship between the magnetic coercive force before heat treatment or after heat treatment
• Example 2 the extrusion (pushing-out) effect on the grain boundary phase by pressurization during the heat treatment is demonstrated.
• a Ta buffer layer was deposited on a Si substrate, a NdFeB layer having a thickness of roughly 5 urn was deposited on the Ta buffer layer, and a Ta cap layer was deposited on the NdFeB layer. All depositions were performed at 450°C using high rate sputtering.
• Heat treatment of crystallization was performed at 750°C. Thereafter, the magnetic characteristics were evaluated by Vibrating Sample Magnetometry, and the microstructure was observed by SEM.
• Figs. 12 and 15 show the cross-sectional SEM images and coercivity measurements of the NdFeB layers. From this Figure, it can be seen that the low
• coercivity ( 18kOe) film has a poor quality buffer layer - substrate interface, and that the magnetic film has almost fully peeled off the substrate. The degradation of the interface is attributed to diffusion between the Ta layer and the substrate.
• the high coercivity (26kOe) film has an intact buffer layer - substrate interface, so that the film is rigidly attached to the substrate.
• the Nd-rich phase becomes liquid during the post- deposition annealing step.
• the high level of compressive stress in the fully adhered film leads to a squeezing out of some of the Nd-rich phase from the hard magnetic layer, which in turn creates ripples in the Ta capping layer (Fig. 14 (a) ) .
• no significant squeezing out occurs in partially released films (Fig. 14 (b) ) .
• Figs. 14(a) and 14(b) are SEM images (secondary electron image) .
• the extrusion of the Nd-rich phase which leads to the formation of surface ripples, also serves to redistribute the Nd-rich phase around the solid Nd 2 Fei 4 B grains.
• the improvement of the magnetic coercive force is attributable to the fact that the grain boundary phase, which is unevenly distributed mainly in triple points among crystal grains of the main phase, is extruded from the triple points due to a compressive stress, and thereby diffusion or fluxdxzation of the grain boundary phase can be accelerated.
• a production method of a rare earth magnet which is usually
• neodymium magnet Nd 2 Fei 4 B
• neodymium magnet films with applications in micro-systems wherein a heat treatment method capable of enhancing the magnetic characteristics, particularly the magnetic coercive force, is used.

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