A permanent magnetic material

Abstract

There is presented a method for providing a permanent magnetic material comprising hexagonal ferrites, which method does not necessitate neither large magnetic fields nor organic solvents. The produced permanent magnetic materials have excellent properties, in particular in terms of energy product, such as in terms of energy product and density. In further aspects, the invention relates to particles for providing the permanent magnetic material, and a corresponding method of manufacture. In particular embodiments of the invention the hexagonal ferrite is given by CaFe 12 O 19 , SrFe 12 O 19 or BaFe 12 O 19 , such as given SrFe 12 O 19 or BaFe 12 O 19 .

1 . A method for preparing a permanent magnetic material comprising hexagonal ferrite, the method comprising:
 obtaining particles comprising hexagonal ferrite, which particles have an anisotropic shape and;   compacting the particles into a permanent magnetic material;   
       wherein the compacting of the particles comprises applying a pressure above atmospheric pressure and a temperature above room temperature, and wherein a size of the particles after compacting are smaller than or equal to a size enabling individual particles to become single domain magnets. 
     
     
         2 - 53 . (canceled) 
     
     
         54 . The method according to  claim 1 , wherein the hexagonal ferrite comprises XFe 12 O 19 , where X is an element selected from the group consisting of Calcium (Ca), Strontium (Sr) and Barium (Ba). 
     
     
         55 . The method according to  claim 1 , wherein
 obtaining particles comprising hexagonal ferrite, which particles have an anisotropic shape, comprises obtaining particles comprising hexagonal ferrite, wherein the anisotropic shape is a plate like shape, and wherein the size of the particles is at most 100 nm.   
     
     
         56 . The method according to  claim 1 , wherein the method comprises reducing or breaking a magnetic interaction between the particles when compacting the particles and/or during compacting the particles, so as to allow alignment of the particles when compacting the particles and/or during compacting the particles. 
     
     
         57 . The method according to  claim 1 , wherein the method comprises:
 pre-heating of the particles, wherein said pre-heating comprises applying a pre-heating temperature above room temperature to said particles before compacting the particles, so that a temperature of said particles is the pre-heating temperature when the compacting is initiated.   
     
     
         58 . The method according to  claim 1 , wherein the particles are enlarged during the step of compacting the particles. 
     
     
         59 . The method according to  claim 1 , wherein the compacting of the particles comprises uniaxial hot pressing. 
     
     
         60 . The method according to  claim 1 , wherein the compacting of the particles comprises spark plasma sintering (SPS). 
     
     
         61 . The method according to  claim 1 , wherein the pressure is at least 20 MPa. 
     
     
         62 . The method according to  claim 1 , wherein a pulsed DC current is applied so as to heat the particles at a rate of at least 10° C./min. 
     
     
         63 . The method according to  claim 1 , wherein the particles are heated to a temperature of at least 800° C. 
     
     
         64 . The method according to  claim 1 , wherein at least partially during compacting the particles into a permanent magnetic material:
 the particles are heated to a temperature of at least 800° C., and   the pressure is at least 20 MPa.   
     
     
         65 . The method according to  claim 1 , wherein a pulsed DC current is applied to heat the particles to a temperature of at least 800° C. 
     
     
         66 . The method according to  claim 1 , wherein the temperature above room temperature is held for at least 1 minute, before cooling to room temperature. 
     
     
         67 . The method according to  claim 1 , wherein the obtaining of particles, comprises:
 preparing particles by:   forming a precursor solution comprising elements of the hexagonal ferrite, and feeding the precursor solution, into a supercritical reactor, so as to carry out a supercritical synthesis of the particles, wherein the particles have an anisotropic shape and wherein the size of the particles are smaller than or equal to a size enabling individual particles to become single domain magnets, or   obtaining particles comprising hexagonal ferrite for a magnetic material, wherein the particles have an anisotropic shape and wherein a size of the particles are smaller than or equal to a size enabling individual particles to become single domain magnets.   
     
     
         68 . The method according to  claim 1 , wherein the method further comprises annealing the permanent magnetic material. 
     
     
         69 . A permanent magnetic material comprising particles comprising hexagonal ferrite, wherein a size of the particles are smaller than or equal to a size enabling individual particles to become single domain magnets, 
       and wherein the particles have an anisotropic shape, and wherein 
       crystallites in the permanent magnetic material have a preferential orientation. 
     
     
         70 . The permanent magnetic material according to  claim 69 , wherein impurities, in the permanent magnetic material contribute to less than 3 wt %, or less than 1.5 wt %. 
     
     
         71 . The permanent magnetic material according to  claim 69 , wherein dimensions of the particles are at least 2 times larger, along a first crystal axis (a-axis) and/or a second crystal axis (b-axis) relative to a dimension along a third crystal axis (c-axis). 
     
     
         72 . The permanent magnetic material according to  claim 69 , wherein the hexagonal ferrite comprises XFe 12 O 19 , where X is an element selected from the group consisting of Calcium (Ca), Strontium (Sr) and Barium (Ba). 
     
     
         73 . The permanent magnetic material according to  claim 69 , wherein a texture index of the permanent magnetic material is at least 2. 
     
     
         74 . The permanent magnetic material according to  claim 69 , wherein a ratio J r (0°)/J r (90°) is at least is at least 2 wherein said ratio J r (0°)/J r (90°) is a ratio between
 a first remanence value J r (0°) obtained at a first orientation of the permanent magnetic material with respect to an external magnetic applied field, and 
 a second remanence value J r (90°) obtained at a second orientation of the permanent magnetic material with respect to the applied external magnetic field, wherein the second orientation is orthogonal to the first orientation. 
 
     
     
         75 . The permanent magnetic material according to  claim 69 , wherein a relative orientation of crystallites within the permanent magnetic material is at least 10%. 
     
     
         76 . The permanent magnetic material according to  claim 69 , wherein a preferential orientation is with c-axis lattice planes parallel to each other. 
     
     
         77 . The permanent magnetic material according to  claim 69 , wherein crystallites in the permanent magnetic material have a length along a third crystal axis (c-axis) of less than 250 nm. 
     
     
         78 . The permanent magnetic material according to  claim 69 , wherein crystallites in the permanent magnetic material have a length along a first crystal axis (a-axis) and/or second crystal axis (b-axis) of less than 250 nm. 
     
     
         79 . The permanent magnetic material according to  claim 69 , wherein the permanent magnetic material has an energy product (BH max ) of more than 11 kJ/m 3 . 
     
     
         80 . The permanent magnetic material according to  claim 69 , wherein the permanent magnetic material has a density of at least 2.0 g/cm 3 . 
     
     
         81 . A device for inter-converting between electrical energy and kinetic energy, wherein the device comprises:
 a permanent magnetic material prepared by:   obtaining particles comprising hexagonal ferrite, which particles have an anisotropic shape; and   compacting the particles into a permanent magnetic material;   wherein the step of compacting of the particles comprises applying a pressure above atmospheric pressure and a temperature above room temperature, and wherein a size of the particles after the step of compacting are smaller than or equal to a size enabling individual particles to become single domain magnets; or   a permanent magnetic material comprising particles comprising hexagonal ferrite, wherein a size of the particles are smaller than or equal to a size enabling individual particles to become single domain magnets, and wherein the particles have an anisotropic shape, and wherein crystallites in the permanent magnetic material have a preferential orientation.   
     
     
         82 . A method for preparing particles comprising hexagonal ferrite, for a magnetic material, the method comprising:
 forming a precursor solution comprising elements of the hexagonal ferrite, and   feeding the precursor solution, into a supercritical reactor, so as to carry out a supercritical synthesis of the particles, wherein the particles have an anisotropic shape and wherein the size of the particles are smaller than or equal to a size enabling individual particles to become single domain magnets.   
     
     
         83 . The method according to  claim 82 , wherein the supercritical synthesis comprises heating of the precursor solution, and wherein said heating is achieved by raising the temperature at a rate of at least 10° C./second. 
     
     
         84 . The method according to  claim 82 , wherein a reaction time period during the supercritical synthesis is 10 minutes or less. 
     
     
         85 . The method according to  claim 82 , wherein the hexagonal ferrite comprises XFe 12 O 19 , where X is an element selected from the group consisting of Calcium (Ca), Strontium (Sr) and Barium (Ba). 
     
     
         86 . The method according  claim 82 , wherein the forming of the precursor solution comprises dissolving a compound comprising iron (Fe), and/or dissolving a compound comprising strontium (Sr). 
     
     
         87 . The method according to  claim 82 , wherein the forming of the precursor solution comprises dissolving iron nitrate, and strontium nitrate. 
     
     
         88 . The method according to  claim 82 , wherein the precursor solution has a X:Fe ratio of 1:1 or R x :1, where R x  is a number 0.1-2 and, wherein the precursor solution has a Sr:Fe ratio of 1:1. 
     
     
         89 . The method according to  claim 82 , wherein the method further comprises adding a base to the precursor solution, wherein a concentration of Fe 3+  iron(III) within the precursor solution when adding the base is within 0.05-0.750 M. 
     
     
         90 . The method according to  claim 82 , wherein the method further comprises adding a base to the precursor solution, wherein a concentration of Fe 3+  iron(III) within the precursor solution when adding the base is within 0.05-0.750 M, and wherein a final concentration of the precursor is 0.05-0.50 M and is achieved through dilution with base and/or water. 
     
     
         91 . The method according to  claim 82 , wherein the forming of the precursor solution comprises:
 dissolving iron nitrate, and/or   
       dissolving a nitrate selected from the group consisting of strontium nitrate, barium nitrate, and calcium nitrate, wherein an alkaline solution is added in a concentration being at least 1.00 times, 1.50 times, or 2 times the concentration of nitrates. 
     
     
         92 . The method according to  claim 82 , wherein an alkaline solution is added in a concentration being at least 1.25 times, the concentration of nitrates from both the iron nitrate and the strontium nitrate. 
     
     
         93 . The method according to  claim 91 , wherein the alkaline solution comprises a substance selected from the group consisting of NaOH, KOH and LiOH. 
     
     
         94 . The method according to  claim 91 , wherein the alkaline solution is added drop wise under constant stirring until a dark red precipitate is formed. 
     
     
         95 . The method according to  claim 82 , comprising feeding the precursor solution, into a supercritical reactor. 
     
     
         96 . The method according to  claim 82 , comprising feeding the precursor solution into a supercritical reactor, wherein the precursor solution is fed into the supercritical reactor at the flow rate of within 0.5-50 mL/min. 
     
     
         97 . The method according to  claim 82 , comprising feeding deionized water into the supercritical reactor at a flow rate of within 0.15-150 mL/min. 
     
     
         98 . The method according to  claim 82 , comprising:
 feeding the precursor solution into the supercritical reactor, at a first flow rate, and   feeding deionized water into the supercritical reactor at a second flow rate, wherein the ratio of the first flow rate and the second flow rate is between 1:0.3 and 1:30.   
     
     
         99 . The method according to  claim 97 , wherein the precursor solution and the deionized water meet at a mixing point. 
     
     
         100 . Particles comprising hexagonal ferrite for a magnetic material, wherein the particles have an anisotropic shape and wherein a size of the particles are smaller than or equal to a size enabling individual particles to become single domain magnets. 
     
     
         101 . Particles according to  claim 100 , wherein the hexagonal ferrite comprises XFe 12 O 19 , where X is an element selected from the group consisting of Calcium (Ca), Strontium (Sr) and Barium (Ba). 
     
     
         102 . Particles according to  claim 100 , wherein dimensions of the particles may be described by dimensions along a first crystal axis (a-axis), a second crystal axis (b-axis) and a third crystal axis (c-axis), and wherein dimensions of the particles are substantially larger along the first crystal axis (a-axis) and/or the second crystal axis (b-axis) relative to a dimension along the third crystal axis (c-axis). 
     
     
         103 . Particles according to  claim 100 , wherein dimensions of the particles are at least 2 times larger, along a first crystal axis (a-axis) and/or a second crystal axis (b-axis) relative to a dimension along a third crystal axis (c-axis). 
     
     
         104 . Particles according to  claim 100 , wherein a dimension of the particles along a first crystal axis (a-axis) is within 20-40 nm, and wherein a dimension along a second crystal axis (b-axis) is within 20-40 nm, and wherein a dimension along a third crystal axis (c-axis) is within 2-4 nm. 
     
     
         105 . Particles according to  claim 100 , wherein an energy product (BH max ) of the particles is at least 0.1 kJ/m 3 .