Developing bulk exchange spring magnets

Abstract

A method of making a bulk exchange spring magnet by providing a magnetically soft material, providing a hard magnetic material, and producing a composite of said magnetically soft material and said hard magnetic material to make the bulk exchange spring magnet. The step of producing a composite of magnetically soft material and hard magnetic material is accomplished by electrophoretic deposition of the magnetically soft material and the hard magnetic material to make the bulk exchange spring magnet.

Claims

1. A method of making a bulk exchange spring magnet, comprising the steps of: providing a magnetically soft material component made of nanometer size magnetically soft materials, providing a hard magnetic material component made of nanometer size hard magnetic materials, producing a composite of said magnetically soft material component and said hard magnetic material component by electrophoretic deposition of said nanometer size magnetically soft materials and said nanometer size hard magnetic materials, controlling said electrophoretic deposition of said nanometer size magnetically soft materials and said nanometer size hard magnetic materials to provide a separation between said magnetically soft material component and said hard magnetic material component, and controlling said electrophoretic deposition of said nanometer size magnetically soft materials and said nanometer size hard magnetic materials so that said separation between said magnetically soft material component and said hard magnetic material component is smaller than a Bloch wall to make the bulk exchange spring magnet.

2. The method of making a bulk exchange spring magnet of claim 1 wherein said step of providing a hard magnetic material component comprises providing a hard magnetic material component made of nanometer size hard magnetic materials including rare earths and wherein said hard magnetic material component contains less than twenty atomic percent rare earths of said hard magnetic material component.

3. A method of producing an exchange spring magnet, comprising the steps of: providing a magnetically soft material component made of nanometer size magnetically soft materials, providing a hard magnetic material component made of nanometer size hard magnetic materials, producing a composite of said magnetically soft material component and said hard magnetic material component by electrophoretic deposition using an electrophoretic deposition device to produce said composite of said nanometer size magnetically soft materials and said nanometer size hard magnetic materials, controlling said electrophoretic deposition device and said electrophoretic deposition of said nanometer size magnetically soft materials and said nanometer size hard magnetic materials to provide a separation between said magnetically soft material component and said hard magnetic material component, and controlling said electrophoretic deposition device and said electrophoretic deposition of said nanometer size magnetically soft materials and said nanometer size hard magnetic materials so that said separation between said magnetically soft material component and said hard magnetic material component is smaller than a Bloch wall to produce the exchange spring magnet.

4. The method of producing an exchange spring magnet of claim 3 wherein said step of electrophoretic deposition includes electrophoretic deposition of Nd.sub.2Fe.sub.14B.

5. The method of producing an exchange spring magnet of claim 3 wherein said step of providing a hard magnetic material component comprises providing a hard magnetic material component made of nanometer size hard magnetic materials including rare earths and wherein said hard magnetic material component contains less than twenty atomic percent rare earths of said hard magnetic material component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the specific embodiments, serve to explain the principles of the invention.

(2) FIG. 1 is a flow chart illustrating the making of a bulk exchange spring magnet of the present invention.

(3) FIGS. 2A and 2B are graphs of the Applied Magnetic Field vs Magnetic Induction illustrating hysteresis loops. FIG. 2A shows a high remanence soft magnet and much harder magnet with a lower remanence, with the hatched area representing the energy density (product). FIG. 2B shows an exchange spring magnet consisting of the hard and soft magnets demonstrating improved remanence, coercivity, and a much larger energy density as illustrated from the cross hatched area.

(4) FIGS. 3A and 3B illustrate electrophoretic deposition (EPD).

(5) FIG. 4 is an illustration of the prior art.

(6) FIG. 5 illustrates the making of a bulk exchange spring magnet of the present invention built up brick by brick with the separation between the hard particles being smaller than a Bloch wall.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(7) Referring to the drawings, to the following detailed description, and to incorporated materials, detailed information about the invention is provided including the description of specific embodiments. The detailed description serves to explain the principles of the invention. The invention is susceptible to modifications and alternative forms. The invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.

(8) Referring now to the drawings and in particular to FIG. 1, a flow chart illustrates one embodiment of a method of making a bulk exchange spring magnet of the present invention. The method is designated generally by the reference numeral 100.

(9) As illustrated in FIG. 1, the method 100 includes a number of steps. In step 102 a magnetically soft material is provided. In step 104 a hard magnetic material is provided. In various embodiments of the invention the hard magnetic material contains less than twenty atomic percent rare earths.

(10) In step 106 a composite of said magnetically soft material and said hard magnetic material is produced. In step 108 the composite is used to make the bulk exchange spring magnet. In step 106 a hard magnet and a soft magnet are combined on the nanoscale to exploit the advantages of eacha larger magnetic remanence/saturation coupled to a large coercivity. Step 106 requires the reliable creation of both hard and soft magnetic materials on the nanometer scale (<10 nm) and that can control their deposition so that they are built up brick by brick with the separation between the hard particles being smaller than a Bloch wall, which is the distance over which the alignment of moments can flip. Step 106 exploits electrophoretic deposition, which allows nanoscopic control of particle position.

(11) Referring now to FIGS. 2A and 2B, graphs of Applied Magnetic Field vs Magnetization illustrate hysteresis loops showing a high remanence soft magnet and much harder magnet with a lower remanence (dashed line). The figure of merit for a permanent magnet is the energy product (or energy density), E, which describes the potential amount of work one can extract from the magnet. This value is determined by the maximum of (BH) in the second quadrant of the magnet's hysteresis loop, also known as the demagnetization curve, where H is the magnetic field strength and B is the magnetic induction. These two terms are related by the equation B=.sub.o(H+M), where M is the magnetization and .sub.o is the permeability of free space (410.sup.7 Tm/A), a constant. (BH).sub.Max.sub.oMs.sup.2/4, where M.sub.s is the saturation magnetization, so this is a limiting factor for the energy density.

(12) There are magnets with very high remnant magnetization (the magnetization that remains when the applied field is removed), that however have very low coercivities (the point at which the magnetization goes to zero), and so are known as soft magnets. Materials that have very high coercivities are hard magnets.

(13) The ideal magnet would have an extremely large remnant magnetization and a very high coercivity, thus maximizing the overall energy product. In reality, there are compromises made between maximizing the coercivity and remnant magnetization.

(14) The present invention provides an exchange spring magnet wherein a hard magnet and a soft magnet are combined on the nanoscale to exploit the advantages of eacha larger magnetic remanence/saturation coupled to a large coercivity. FIG. 2A shows the respective energy densities for a soft and hard magnet, given by the hatched areas. The material of the present invention is represented by the cross-hatched area of FIG. 2B, demonstrating a much larger energy density. The present invention reliably creates both hard and soft magnetic materials on the nanometer scale (<10 nm) and controls their deposition so that they are built up brick by brick with the separation between the hard particles being smaller than a Bloch wall, which is the distance over which the alignment of moments can flip. The present invention exploits electrophoretic deposition, which allows nanoscopic control of particle position.

(15) The challenge in producing high performing ESMs has been the inability to precisely control the spacing of the particles and the coupling between them. Electrophoretic deposition (EPD) is a processing method which utilizes the induced surface charge particles exhibit when placed in both aqueous and organic liquids. The surface charge is then used to control the motion of the particles in suspension in the presence of electric fields. As such, EPD is the particle level equivalent of electroplating and permits the precise control of particles needed to manufacture superior ESMs with energy products approaching the theoretical maximum.

(16) By controlling certain characteristics of formation of structures in an EPD process, such as the precursor material composition (e.g., homogenous or heterogeneous nanoparticle solutions) and orientation (e.g., non-spherical nanoparticles), deposition rates (e.g., by controlling an electric field strength, using different solvents, particle concentration, etc.), material layers and thicknesses (e.g., through use of an automated sample injection system and deposition time), and deposition patterns with each layer (e.g., via use of dynamic electrode patterning), intricate and complex structures may be formed using EPD processes that may include a plurality of densities, microstructures (e.g., ordered vs. random packing), and/or compositions, according to embodiments described herein.

(17) Referring now to FIG. 3A, an electrophoretic deposition (EPD) device is illustrated. The EPD device is designated generally by the reference numeral 300. The EPD device 300 includes a first electrode 302 and a second electrode 304 positioned on either side of an EPD chamber 306, with a voltage difference 308 applied across the two electrodes 302, 304 that causes charged particles 310 in a solution 314 to move toward the first electrode 302. In some embodiments, a substrate 312 is placed on a solution side of the first electrode 302 such that particles 310 collect thereon. The EPD device 300 is used to attract particles 310 toward the first electrode 110 or toward the conductive or non-conductive substrate 312 positioned on a side of the electrode 302 exposed to a solution 314.

(18) Referring now to FIG. 3B, additional details about the EPD device and EPD process is illustrated. The EPD device is designated generally by the reference numeral 300. The EPD device 300 is used to attract the particles 310 toward the first electrode 110 or toward the conductive or non-conductive substrate 312 positioned on a side of the electrode 302 exposed to the solution 314.

(19) By controlling certain characteristics of formation of structures in the EPD process, such as the precursor material composition (e.g., homogenous or heterogeneous nanoparticle solutions) and orientation (e.g., non-spherical nanoparticles), deposition rates (e.g., by controlling an electric field strength, using different solvents, particle concentration, etc.), material layers and thicknesses (e.g., through use of an automated sample injection system and deposition time), and deposition patterns with each layer (e.g., via use of dynamic electrode patterning), intricate and complex structures may be formed using EPD processes that may include a plurality of densities, microstructures (e.g., ordered vs. random packing), and/or compositions, according to embodiments described herein.

(20) As illustrated in FIG. 3B, the particles 310 are drawn toward the first electrode 110 and the conductive or non-conductive substrate 312. By controlling the electric field strength and using different solvents the particle concentration is controlled to produce material layers it is possible to produce intricate and complex structures. The changes in particle concentration producing the material layers are illustrated by the areas designated by the arrows 316, 318 and 320. By controlling the electric field 308 and the different solvents 314 the particle concentration is controlled to produce the bulk exchange spring magnet of the present invention. The EPD process is used to provide a first component characterized as a magnetically soft material and a second component characterized as a hard magnetic material. The first component and said second component are deposited by an electrophoretic deposition process to produce a bulk exchange spring magnet that is a composite of said magnetically soft material and said hard magnetic material.

(21) Referring to FIG. 4, the prior art is illustrated. Control of the separation distance between neighboring hard magnets is critical. If they are too far apart, the energy product will be lower than desired. The Bloch wall is defined as the boundary between two domains in a magnetic material marked by a layer wherein the direction of magnetization is assumed to change gradually from one domain to the other.

(22) Referring now to FIG. 5, the making of a bulk exchange spring magnet of the present invention is illustrated. The present invention reliably creates both hard and soft magnetic materials on the nanometer scale (<10 nm) by controlling their deposition so that they are built up brick by brick with the separation between the hard particles being smaller than a Bloch wall, which is the distance over which the alignment of moments can flip.

(23) The present invention provides the production of a stable suspension, of mixed composition, consisting of nanoscale hard magnetic particles such as SmCo5, along with soft iron nanoparticles. This suspension is deposited on to a substrate and consolidated to a dense composite. The composition and microstructure of the final ESM is determined by control of both the composition and deposition rates of the particles in suspension. The present invention provides a practical method to assemble building blocks at the scale of tens of nanometersthe precise range at which magnetic properties are projected to be optimal.

(24) Magnets, through generators and motors, are the primary mechanism for converting between mechanical energy and electrical energy. Improving the strength of magnets will increase the efficiencies while permitting lighter, more compact designs. Such improvements will engender improved regenerative braking systems and can be expected to increase the range of all-electric vehicles making them more commercially viable. Similarly these magnets will allow smaller, lighter, and less expensive turbines for large scale windmills thus reducing both the energetic and financial costs of installation. The development of REE permanent magnets has made many modern devices practical. Without these magnets, the current design of regenerative braking in hybrid automobiles would not be feasible due to the order-of-magnitude increase in size of the non-REE magnets required, and commensurate increase in motor/generator size. Consumer products, such as compact hard disk drives necessary for laptop computers, also rely on high-strength magnets. An improved magnet will reduce the size of motors and generators, permitting efficiency gains in mobile systems due to the reduction in size and weight, and open the way to new applications not currently practical. The annual global market for permanent magnets exceeds $10 billion, with more than half of that value in REE magnets. Bulk ESMs have the potential to replace most of the REE magnet market at a considerably lower overall cost.

(25) While the invention may be susceptible to various modifications and alternative forms, specific embodiments, have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.