JPS63262805A - Manufacture of iron base permanent magnet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention is directed to permanent magnets with controlled magnet retention and methods for economically manufacturing such magnets.

More particularly, the present invention relates to iron alloys with rare earths and boron and a controlled holding field (1
-1c) and energy products (Bt(m)) in the range of 10-18M G Oe.

BACKGROUND OF THE INVENTION The primary permanent magnet material in use today is AlNiCo.
, hard ferrite, rare earth-cobalt stabilized with iron, and rare earth-iron magnets stabilized with birch.

Although AJNiCo and ferrite materials (such as strontium or barium ferrites) have proven to be inexpensive, typically costing about $1.50 per bond of material, their magnetic properties Automatic start! IJ machine motor or magnetic imaging device <cat
5) does not provide a sufficiently high energy product or coercivity to be suitable for applications such as 5 can). Such magnets are energy products of about 4MGOe level, and 4K
It showed a lower level of holding power than Oe.

At the opposite end of the cost spectrum are rare-earth-cobalt-iron and rare-earth-iron-iron magnets, each of which is 1
It has proven to be extremely effective with a cost factor of at least about $80 per bond material. Iron Stabilized Rare Earth-Cobalt Magnets U.S. Pat. No. 4.081.297:4
．． 369.075 and 4,131.495. This type of magnet usually contains rare earths and cobalt in a loss of up to 50-60 heavy metals. Cobalt is a strategic material and the primary source of cobalt for the United States is South Africa, particularly Zaire.

Political considerations therefore often influence the availability and price of cobalt. This type of magnet also contains intermetallic compounds of rare earths and cobalt, which exhibit extremely large magnetocrystalline anisotropy. Energy products of at least about 24 MGOe (several times more than conventional AlNiCo or ferrite permanent magnets) are obtained with samarium-cobalt permanent magnets. Even higher saturation magnetization of intermetallic S
Higher working temperatures can be obtained due to the presence of m2CO17. Even higher energy products were obtained to improve retention by partial substitution of iron or copper. However, two characteristics still exist that hinder the application of such rare earth-cobalt permanent magnets in automatic applications, namely the high cost of the material and the high energy product and/or coercive force field, which makes it difficult to achieve the desired flux density. It goes around once.

In an effort to overcome the need for cobalt, researchers have turned to the use of rare earth-iron magnets stabilized with boron. By choosing certain rare earths to be of lighter, more abundant type, the cost factor was only slightly reduced (US Patent hjX4°541.877; 4.597.
938; 4.585.473). The rare earths selected for these disclosures are 15-20% Nd with boron in the 8-12% range, and in some cases Dy and/or 1-b. Nd ;] was obtained. These materials generally have high coercivity levels and when modified energy production was reduced to 13 MGOe.

To further reduce the cost of obtaining specially refined rare earth raw materials for such permanent magnets, mixed metals (Hi
Sch metal: 8M) was proposed to be used. , mixed metals are more concentrated forms of rare earth metals that are obtained early in the chemical processing of naturally occurring rare earth-containing ores.

The specific composition of the mixed metal depends on the ore used (
Although the ore content will vary to some extent between different geographical locations, it will be essentially the same - the primary rare earths woody; it will represent a uniform amount), a common mixed metal composition. is 5
2% cerium, 20% 1a, 15.7% Nd, 4.8%
Pr, and about 6% rare earths. The mixed metal will have a content that reflects to a large extent the combination of rare earths found in the ore from which it is refined.

Didymium is sometimes referred to as a mixed metal, which is even more costly because it is extracted from the original mixed metal by additional chemical steps. Cerium and lanthanum are the easiest rare earths to remove from mixed metals, so didymium reflects ease of removal at the level of the seed bar. The composition of didymium, which is also common for trowels, is essentially: (i) 90% Nd-10% Pr, (ii) 80% Nd-
5%pr, (iii) 50%Nd-40%(:, e-
10% pr, and (iv) 60%P r = 20%
Composed of Nd-20% La.

Most of the time, when referring to mixed metals as an alternative to introducing rare earth materials, there is no way to do MM work without considering cost or the desired chemistry, and without any samples. (U.S. Patent No. 4.152.17).
8 and 4.090.892). Where chemistry is of some importance, the teaching is limited to the quenching of ribbons of such materials, since inventions with permanent magnets reduce cost and the mixed metals or derivatives are low Nd and/or La Utilize early stage mixed metal products to keep costs low.

In almost all of the current studies in rare earth-iron-boron magnets, the direction is to create a pronounced single-phase magnetic matrix material and to minimize non-magnetic secondary phases. It is to reduce. Rare earth - the second in borosilicate permanent magnets
It was thought by prior art researchers that the appearance of a non-magnetic phase prevents such magnets from having highly reproducible magnetic parameters. Therefore, subsequent attempts were made to reduce the appearance of non-magnetic second phases.

There is an increasing need for permanent magnets that are lightweight and at the same time economical and adaptable to special applications with increased performance.

The development direction of the present invention is to provide a permanent magnet of the Fe-B-MM type, which uses a double magnetic phase in a new and advantageous way and redistributes the non-magnetic phase in a new way. Known iron-
0 from boros - rare earth (Fe-B-R) or rare earth -
Significantly lower cost than cobalt type magnets, and still preferably exhibit energy production in the range of 14-17 MGOe and retention in the range of 5-8 KOe.

It is a particular object of the present invention to provide a permanent magnet of the iron-rare earth type stabilized with boron, which contains (i) an increased or significant proportion of iron in the range of 60-80% atomic weight; (ii) significantly reduces the cost of such materials over what was possible with the prior art using 12-22% mixed metals and 6-10% boron, and (ili) Phase redistribution agents are used to increase the coercivity and energy production of such materials to promote interfering phases to larger area wall anchoring.

The present invention is a method for making permanent magnets of the Fe-B-MM type, comprising: (a) an average particle size of about 2 microns or greater and an atomic weight of %: 12-22;
% mixed metal, 1-8% Al, 6-10% 8,0.
less than 43% oxygen, up to 5% displacer Dy as a substitute or adduct of mixed metals and/or up to 10% N1 as a partial substitute or adduct of Al, physical properties other than magnetic having a composition consisting essentially of up to 3-10% modifier for modification, and the balance Fe, wherein the substitutability and/or modifier is present with substantially at least 60% Fe. The powder has an essentially multiphase crystal structure dominated by at least two R2Fe14B phases and the mixed metal preferably contains at least four naturally occurring insoluble cerium rare earth metals and cerium and/or or containing at least 20% of such rare earth metals consisting of lanthanum):
(b) aligning such powders in a magnetic field; (c) shrinking the aligned powders into a shape, preferably a block, arc, cube or cylinder; (d) forming such a shape into ( The powder is sintered at a temperature (preferably in the range 1000-1100°C) for a period of time to melt, redistributing the phases and increasing the proportion of the R2Fe14B phase to at least 7% of the shape.
and preferably (e) sintered shapes are annealed at 7 m degrees in the range of 550-650 °C to form a microstructure consisting essentially of iron and the magnetic phase R2F814B in the matrix. and a high proportion of non-magnetic phase RFe4B4 and rare earth π phase ([!lchi, R-Fe-
0) is caused at grain boundaries.

The resulting permanent magnet cylinder is characterized by the magnetic media of commercial FJ light magnets and commercial R-F e- (Type 3 magnets, where R is essentially composed of a high proportion of Nd). The present invention may be applied to aluminum,
DV and/or N of mixed metals and/or pebbles
Replace Nd depending on the combination of i. It has been found that by this substitution and the process control parameters of the present application, permanent magnets having magnetism in the middle range can be manufactured at low cost. Rare earth Dy is oxide (Dy203)
When added as 2% to 5%, the total content of Dy in the mixture is in the limited range of 5%.

The present invention provides a more economical permanent magnet of the Fe-B-MM type, which has a controlled coercivity that is more effectively adapted to the needs of automatic type applications;
Controlled coercive field in the range of KOe, 10-11
Energy generation in the range 0-l7, at least 65Em
It is made from an alloy powder designed to have a Ms of u/g and a TO of preferably at least 250°C. ``The magnets of the present invention are made by powder metallurgy techniques and are based on iron-mixed metals (more than 70% by weight). Iron is one of the most abundant elements on earth and is extremely inexpensive. Mixed metals are also significantly less expensive because they do not require a purification step for much higher purity rare earth elements (such as neodymium). Boron acts as a fluxing agent for sintering.

The coercive field is significantly increased by the controlled addition of Al, which promotes the immobilization of the S phase or the binary iron-rich phase or the redistribution of the non-magnetic phase. ΔO can be added as an element to the melt for the mold as 10 aluminum.

Dy substitution or addition in place of MM is carried out in the melt or in the as-cast sample, i.e. by addition of the element Dy or by blending the as-cast powder with Dy203 (which is very cheap) and Next proceed with alignment, compaction and sintering steps.

Ni and other modifiers, such as up to 3% Cr or up to 10% cobalt for corrosion resistance, can be added as elements to the as-cast mold.

Chemical composition, control of such composition during processing, and heat treatment lead to special microstructures with multiphase (magnetic) systems. It has only one dominant magnetic phase (Fe14Nd2B
) is completely different from the Fe-Nd-8 microstructure observed.

For the purposes of the preferred method, arc-shaped molten lumps (
(under argon atmosphere) in atomic weight%: 12-22% MM
, 1-8% Al, 6-10% B up to 15% Dy and/or 10% Ni1 up to 3-10% to modify physical properties other than magnetic properties as a substitute or adduct of MM or Fe, respectively of drug, 0.1-0.43% oxygen, and balance Fe, and iron at least 60%
It is formed from a starting melt consisting essentially of. Mixed metal as used herein refers to a material of at least four naturally occurring infusible seri-cum rare earth metals, with at least 20% of such rare earth metals being composed of cerium and/or lanthanum. Cerium rare earth metal is La, Ce, Pr, Nd, Sm
, and SC, such metals are often referred to as light rare earth metals. The mixed metal will typically contain 3-4% heavy rare earth metals.

Such a mixed metal is derived from Indian origin and analysis shows 52% Ce, 20% La, 15.7% Nd, 4.8
%pr, containing 3-4% heavy rare earth metals. Synthetic mixed metal (named didymium) is 60% pr, 0%
Co, 20% 1-a and 20% Nd: 40% Ce, 0
%l,a, 50%Nd, and 10%Pr: 90%N(
j, O% Qe.

0% l-a and 10% Pr: 5% Ce, 0% La.

It is designed to contain 80% Nd and 15% pr. , such synthetic mixed metals resulted from the removal of Ce and/or 1-a. For the purposes of the present invention, Ce
Only didymium with a 20% reduction will be sufficient for use in the method described herein.

The present invention advantageously and preferably uses mixed metals originating from the early stages of rare earth ore processing before removal of Ce or la. However, some of the didymium can be used as indicated, as long as Ce and/or La (rarely resulting from later stages of processing) constitute at least 20% of the didymium.

Mixed metals are often produced by concentrating monazite ore into a concentrated combination of rare earth salts, and these commodity salts are then converted to chlorides and then NaCj!
or applied to the electrolysis of anhydrous rare earth chlorides so molten in KCl (W, 11.Dennis, cited in U.S. Pat.
54), or Concave Metals Handbook,
C11fford tlaipel, chapter 16 (195
(See 4).

The introduction of aluminum is critical to the present invention at 5F °C because it promotes the redistribution of the non-magnetic phase (the rare earth-rich phase, denoted R-Fe-0, is at about 600 °C
(formed at temperature levels of ), primarily at grain boundaries and promoting double magnetic interphase disturbance as a result of such redistribution. If less than 1% aluminum cum is present, the coercivity will fail to increase during sintering. If more than 8% aluminum is added, residual and TO will work inversely.

If less than about 6% of boronate is used, RFe14B
It will fail to form a phase and will adversely affect the magnetic properties of the shape if added in amounts greater than 10%.

A small charge of Dy, either as an oxide or as a rare earth metal, can increase the coercivity field beyond that obtained with mixed metals: aluminum or mixed metals at the lower end of the range. It is desirable to increase the resulting coercive force loss beyond what is reasonably possible. Ni is added as a substitute or adduct to Fe and functions to increase coercivity when Al or mixed metals are added at the low end of a given knot. However, the chemical system can work regardless of the presence of Dy or Ni. , if Dy is added in amounts less than 1%, the desired benefits of increased anisotropy and increased coercivity field will not be obtained. 7N1 can be used in a similar manner, but with less effectiveness, if a 5% higher amount is added, the residual amount will be reduced.

Modifiers can be added to the melt to increase the corrosion resistance of the magnetic material, for example O-3% chromium, or 0-10%
Cobalt can be added to cucumber to raise the temperature. , modifiers such as molybdenum are added to affect the physical properties of the non-magnetic raw materials, the molds resulting from the orphan melts have a purity of at least 99.8% and their components are purified using argon using a micro-mill. It is first crushed at the bottom. The resulting powder is then ball milled under anhydrous toluene using a crusher to achieve uniform particle size and homogeneous composition. Milling is preferably controlled to yield an average particle size of 2-5 microns, but not less than about 2 micrometers, and specifically a critical particle size of 1.72 micrometers for the desired chemistry.

Sintering, grain size, and oxygen concentration are interrelated factors for the development of harder magnetic properties. Incorrect addition of the castings leads to a reduction in magnetism due to the addition of matched rare earths. Preferably, no vacuum is used during grinding and the powder should not dry out. Retention rah after reduction and sintering
corresponds to a critical grain size, at which point the Fe-MM-B crystallites are strongly influenced by the formation of bulk oxides with a size of 1.7 microns. For powder sizes larger than the critical particle size, all the oxygen is chemisorbed and does not become available to reduce the rare earth content.

For powder particles smaller than the critical powder size, oxygen is partially chemisorbed and partially in the form of bulk oxides. The corresponding critical maximum oxygen concentration promoting superior properties for the type of alloy considered for the present invention is 0.4
It was found to be 3% by weight. Magnetic performance is increased by controlling particle size, liquid torne coating, and powder participation through lower sintering temperatures.

Preparation of shapes for subsequent sintering The alloyed powder mixture must be protected against oxidation: it is preferably protected by a liquid cover of toluene or other inorganic solvent protectants, i.e. The powder is added in leaky quantities with not significantly more liquid.

Wet the powder by weighing a predetermined amount of mold and placing it in a magnetic field for 5-5 minutes.
Align in the range y0 of 10KOe. These weighed masses are subsequently and gradually compressed to about 5000 bonds in a compression die in a direction perpendicular to the applied magnetic field, allowing escape of the toluene. Preferably, the shape is compressed into a block, cube, cylinder or arc. The pressure at which the powder mixture is compressed is approximately 50,000 Dsi (40
,000-60,000DS+) and 70-80
% pre-sintered density. The shapes are characterized by a predominant magnetic phase designated R2Fe14B in the green body, which is present in an amount of approximately 65-75%. The remainder of the green body consists of the non-magnetic phases R+:e4B4 and Rx-Fe-0 (rich in rare earths), where X is at least 30-40. The magnetic properties of such raw bodies are energy products 1
0-110-15, and the coercive force is about 7.0 KOe.

Sintering and subsequent heat treatment The pressurized shape is heated in high vacuum (i.e., 10-4 Torr or higher), preferably in stages, the first being about 4 Torr or higher.
All of the toluene is degassed at 00°C for 8-15 minutes, and then at a temperature range of 1000-1100°C for 0.5-9 hours (preferably 1 hour). The shapes were then heated to room temperature using a flush of argon (high purity) at 100-2
Quench at a quenching rate of 00°C/min. Sintering is performed in a high vacuum of about 10@-4 Torr or higher. Cooling is carried out until the shape is at least below 50°C and preferably 25°C.

Hard magnetic properties are obtained with or without post-sintering heat treatment. Without heat treatment, the process is easier and therefore much cheaper, but the Hc is a little lower.

The heat treatment consists of heating in high vacuum at a temperature level of 550-650° C. for about 1-4 rII (preferably 190 minutes), followed by cooling with a flush of argon.

The resulting permanent magnet has a crystalline microstructure and is characterized by a matrix dominated by at least two RFe14B phases; illustratively, one with light rare earths and the other with heavy rare earths. This results in distinctly different magnetic properties.

Since each of the R2Fe14B phases has different magnetic properties, their simultaneous existence is the domain wall 1i! It turns to create an i+ constant, which leads to an increase in coercive force. This is clearly reflected in the effective initial Kerr 11 of the demagnetized samples A, C, where a critical magnetic field exists, below which the domain walls are not fixed, leading to an increase in magnetization.

The non-magnetic phase will constitute 15-20% by volume of the final material, with the rare earth-rich phase predominating at the grain boundaries. The increasing redistribution of the non-magnetic phase to the grain boundaries is a unique feature of the present invention. One such resultant feature of interest is the thermal magnetization feature.7 Generally square or rectangular hysteresis loops, the uniformity of the coercive horns depends on the two R
This suggests that the presence of the Fe14 phase is responsible for the fixation of W4mt, leading to such hysteresis being square, and that this microstructure fixes the domain wall against slippage. and thus lead to high standards of retention and survivability.

The crystalline size of the resulting permanent magnet will be in the range of 5-10 microns. Essentially, 70-75% of the magnetic material is an iron-rich dark ferromagnetic phase, 1-5%
The two non-magnetic phases of V&O will exist essentially in the grain boundaries, a ferrous-rich phase and a rare earth-rich phase of about 15-19%.

EXAMPLE A significant amount of experimentation has been conducted to develop unique processing parameters that work best with the chemistry of the present invention.

Such processing controls are best described as
Oxidation protection with toluene and high vacuum, control of average particle size of approximately 2 microns, degassing, sintering at 1040°C for 1 hour, cooling with argon flushing, and
Optimization was achieved by the use of annealing at 50° C. for 2 hours followed by cooling with argon flushing.

Data for optimization of such process parameters are not given in the table. The data given in Tables I and II demonstrate the chemistry necessary to function with such processing. Approximately 1 arc melted for each sample
The 00 st ingot was first crushed by applying it to a micromill and then a ball mill under argon for varying times to give an average particle size of about 2 microns and an oxygen content of about 0.4%. 7I-lumil treatment was carried out using a mill under moisture-free toluene to achieve uniform particle size and homogeneous composition. Particle size and oxygen fraction were determined using micrographs obtained by a Jeol 100G scanning electron microscope. In all cases iron was present in the range of 60-80 atomic weight percent as a residue of chemical processing.

In Table 1, the rare earth composition throughout the samples was varied using various combinations of mixed metals with changes in the matrix of aluminum and the presence or absence of Dy or Ni.
The use of a post-heat treatment (annealing) was generally practiced but sometimes omitted as indicated. The effectiveness of these variables is Hc (KOe), Ms (Emu/g) and Tc
This was reflected in the level of ('C).

Although all of the samples listed in Table 1 fall within the broad working chemistry scope of the present invention, the samples in Table 2 do not fall within the scope of the present invention.

Sample 1-8 in Table 1 is MM with B kept at 8-10%.
While keeping A at the high end of the inventive range (18-22%)
The effect of changing l will be explained. Sample 5 shows the effect of not using post-heating (7 rings). Sample 9-21 is Dy
(added as oxide after grinding the alloy powder) to MM and or Aj! It is shown with the change of erasure. Samples 22-27 represent the use of Ni as an adduct to Al, MM and/or Dy.

In Table 1, Sample 1 shows the properties of the standard Fe-Nd-8wJ material. Sample 2 shows the effect of using Nd and MM. Samples 3 and 5-10 illustrate the exclusion of Al. Samples 5-8 and 11' show the effect of underuse and overuse on MM or B.

Although particular examples of the invention have been illustrated and described, it is understood that various changes and modifications may be made without departing from the invention.
It will be apparent to those skilled in the art that all such changes and equivalents within the scope of the appended claims are within the true spirit and scope of the invention.

,"l (Ot= a:1(7) O-('J ('
)? n Co to r r r t-to
Sample Chemistry
a.

3 16 8 0--Ni-8 510100---1 920803-1 10 20 8 0-1-- 141783---1 Table ■ :

Claims (25)

[Claims] (1) A method of making an iron-based permanent magnet, comprising: (a) a mixed metal having an average particle size of about 2 microns or greater and in atomic weight percent: 12-22%; 8% Al, 6-10% B, less than 0.43% oxygen, 10 as partial substitution or adduct of Dy and/or Al of displacing agents up to 5% as substitution or adduct of mixed metals % Ni, up to 3-10% modifier for modifying physical properties other than magnetism, and the balance Fe, wherein the substitutive and/or modifier is Fe. (b) applying the powder to a magnetic field; (c) compressing the aligned powder into a shape; and (d) sintering the shape at a temperature and time at which the powder melts, redistributing the intermetallic phase, and R_2Fe_1_4
increasing the proportion of phase B to at least 70% by volume of the shape, cooling the sintered shape to a temperature of 50° C. or lower, and dissolving the powder during at least steps (b) to (d). , protecting against oxidation before and during the step. (2) the mixed metal of step (a) comprises at least four naturally occurring insoluble cerium earth metals, and at least 20% of such mixed metal comprises cerium, and lanthanum; The method described in paragraph (1). (3) Claim (1) wherein said powder is made of an alloy of Fe-Al-MM-B and said Dy, if present, is added to said powdered alloy as an oxide. How to describe. (4) in step (d) the cooling is performed at a rate of 100-200 per minute;
A method according to claim 1, which is carried out at a rate of .degree. (5) additionally comprising the step (e) of annealing the sintered shape to a temperature in the range of 550-650° C. for 1-4 hours, and then rapidly cooling it to room temperature. ). (6) The sintering and annealing is at least 10^-^4
5. The method according to claim 5, which is carried out during depressurization of Torr. (7) A method according to claim 6, wherein the cooling of step (d) and the quenching of step (e) are carried out by brushing with high purity argon. (8) The sintered shape has a crystal structure and is additionally made of RFe.
Claim No. _4B_4 comprising a non-magnetic phase and a rare earth-rich phase essentially present in the grain boundaries of the alloy.
The method described in section 1). (9) A method according to claim 1, wherein the at least two R_2Fe_1_4B phases have different magnetic properties, causing domain wall pinning and increasing coercive force. (10) Step (b) is carried out by the use of a magnetic field of 5000-8000 Oe.
). (11) Stage (c) is 40.000-60.000 ps
Claim No. (
The method described in section 1). (12) The method according to claim (1), wherein the shaped object is a block, an arc, a cylinder, or a cube. (13) A method according to claim 1, wherein the sintering of step (d) is carried out at a temperature of 1000-1100° C. for 0.5-9 hours. (14) The heat treatment for sintering is carried out in two stages, whereby the molding is heated to about 400° C. for 8-15 minutes and then heated to the sintering temperature.
The method described in section 1). (15) The protection is effected by the use of an antioxidant coating during step (a) and by the use of a vacuum during steps (b) through (d). The method described in. (16) Claim No. 1, wherein the drug is toluene.
The method described in section 5). (17) wherein step (d) is carried out to provide a sintered density greater than 99% of the theoretical density;
The method described in section 1). (18) A method according to claim (1), wherein the crystalline dimensions of the sintered shapes are in the range of 5-10 angstroms. (19) The product resulting from the practice of the method according to claim (1) has a coercivity of at least 4-80e, a residual value of at least 65Emu/g, and a residual value of 10-17MGOe.
of energy products and a Curie temperature of at least 250°C. (20) The method of claim (1), wherein the mixed metal results from electrolysis of molten anhydrous rare earth chloride in NaCl or KCl. (21) The method according to claim (1), wherein the mixed metal is obtained by subjecting a concentrated combination of rare earth salts prepared from monazite ore to electrolysis. (22) A method for producing a permanent magnet material of the Fe-B-MM type, the method comprising: (a) an average particle size of 2-5 microns and, in atomic weight percent: 60-80% Fe, 1-8 % Al, 6-10
% B, and 12-22% MM, where MM includes the naturally occurring insoluble cerium rare earth metal and at least 2%
A metal powder is prepared having an alloy composition comprising a mixed metal comprising at least four elements consisting of 0% MM of cerium and/or lanthanum, the powder being essentially composed of a predominant R_2Fe_1_4B phase. (b) aligning the powder in a magnetic field; (c) compressing the aligned powder into a cylindrical shape; and (d) heating the cylindrical material at 1000-1100°C. A method of manufacturing which increases the proportion of R_2Fe_1_4B phase to at least 75% by volume by sintering at a range of temperatures. (23) Formed by a sintered alloy containing mixed metals, boron, Al and Fe, the sintered alloy is a noeromagnetic phase of 70-75% iron-rich intermetallic compounds, 1-5% by volume. It has a crystalline microstructure with a rare earth-rich phase and about 15-19% rare earth-rich phase, the latter two non-magnetic phases essentially existing in the grain boundaries of the microstructure. magnet. (24) At least two iron-rich phases exist, one of which is
Claim 23, wherein one layer is formed of a heavy rare earth metal and the other layer is formed of a light rare earth metal, the two layers fixing the area walls to increase the holding force. Magnets described in . (25) The magnet has a Hc of 4-8, KOe, at least 6
Physical properties of Ms of 5Emu/g, and 10-17M
Claim No. 2 indicating the energy products of GOe
The magnet described in section 3).