Title of Invention

"A MAGNETIC POLYMER COMPOSITION AND PROCESS FOR THE PREPARATION OF THE SAME"

Abstract

A magnetic polymer composite comprising 60-90% by weight of the polymer and 10 -40 % by weight of magneto-resistive alloys prepared by the process by dissolving 60-90% by weight of the polymer in a solvent to obtain a clear, colourless solution; adding 10 -40 % by weight of alloy in the said clear colour less solution; agitating the said clear, colour less solution at a frequency of 15-20 kHz for a period of 5-30 minutes, to get equally dispersed alloy in the said polymer solution; transferring the said polymer solution with equally dispersed said magneto-resistive alloys to the open non-metallic container on a magneto-stirrer allowing the said solvent to evaporate till the polymer coated transition metal based alloys are isolated in the form of cones from the said non-metallic container.

Full Text

The present invention relates to a magnetic polymer composite and the process for the preparation of the same for the read and write head for use in magnetic storage devices. Preferably, the present invention relates to a process for the preparation of magnetic polymer composite comprising magnetic transition metal based alloy and a processable polymer capable of exhibiting magneto resistive properties. The object of the invention is to fabricate the magneto resistive polymer composite by isolating the components in the form of cones having effective coating of each particle of the magnetic alloys with the layer of polymer. Magnets are well known feature having a wide range of applications in using permanent (hard) or non-permanent magnets. The magneto resistive features are found mainly in two classes of compounds as ferromagnetic alloys and rare earth manganites. However, it has been observed that in both the cases , when the magnetic field is applied , there is remarkable drop in resistance . In the case of ferromagnetic alloys , the resistance varies with the thickness of the spacer and/or the non-magnetic layer, while in case of rare earth manganites, the resistance varies at the magnetic transition temperature. The Ferromagnetic alloys in particular exhibit this behaviour when fabricated as multilayers with alternate stackings of magnetic and non-magnetic layers such as Fe-Cr, Co-Cu, systems. The magnitude of magneto resistance varies as a function of layer thickness of Cr or Cu. However, magneto resistance in Ag-Co system shows that the granular giant magneto-resistance can also be observed wherein clusters of cobalt can be dispersed in a non-magnetic matrix such as silver. Electrically conducting polymer composite material exhibiting positive temperature coefficient of resistance is known in the art. However, polymer composite exhibiting both positive temperature coefficient of resistance and magneto-resistive effect is not known in the art. Hence, the conducting polymer composite materials consisting of a random distribution of a conducting filler throughout an insulating polymer are of interest of several applications. In the subject invention, the analogy of fabricating new systems wherein ferromagnetic compounds are dispersed in a non-magnetic , non-conducting polymer matrix have been developed by proper tailoring of the composite to aid percolation between such particles to obtain ferromagnetic behaviour in such composites. The Chromium is having anti-ferromagnetic property which brings about an anti-ferromagnetic coupling between Fe atoms, making Fe-Cr alloys having magneto-resistive property resulting in the drop of Curie temperature of the Fe as an increase of the Cr doping. Such alloys can be used as conducting fillers in an insulating polymer matrix having electrical, magnetic and magneto-resistive behaviour. The present invention is directed to a method for preparing polymer coated magnetic alloys preferably in the form of cones obtained by dissolving the processable polymer in a solvent and dispersing the alloy in the powder form by agitating the mixed polymeric solution followed by solidification of the polymer coated alloy either in the form of a powder or as oriented cones. The polymer of the subject invention to be coated on the magnetic alloy particles is a Vinyl-keto polymer. The subject polymer is selected due to its complete solubility in the solvent. Accordingly, the subject invention relates to a magnetic polymer composite for the read and write head for use in magnetic storage devices , comprising - 60-90% by weight of the polymer preferably vinyl-keto polymer and - 10 -40 % by weight of alloy preferably magneto-resistive alloys having magnetic properties. The present invention also relates to a process for the preparation of a magnetic polymer composite, comprising dissolving the 60-90% by weight of the polymer preferably vinyl-keto polymer in a solvent by stirring the same in an open atmosphere at ambient temperature to obtain a clear, colourless solution; adding 10 -40 % by weight of alloy preferably magneto-resistive alloys in the said clear colour less solution; agitating the said clear, colourless solution at a frequency of 15-20 kHz for a period of 5-30 minutes, to get equally dispersed alloy in the said polymer solution; transferring the said polymer solution with equally dispersed said magneto-resistive alloys to the open non-metallic container on a magneto-stirrer allowing the said solvent to evaporate till the polymer coated transition metal based alloys are isolated in the form of cones from the said non-metallic container. The said dissolution and mixing of the polymeric material results in effective coating of the said alloy particles. The said agitation is done in a sonicator and the said non-metallic container is preferably a glass container. The polymer coated Iron alloys isolated in the form of cones are having dimensions up to 2mm length and 0.5mm width The said polymer and magneto-resistive alloys used are in the powder form and the polymer used is vinyl-keto polymer , specifically polyvinyl pyrrolidone and the said magneto-resistive alloys are selected from chromium-iron, chromium-cobalt or chromium-nickel . The subject application may better be understood with reference to accompanying drawings. However, the same should not be construed to restrict the scope of the application as they are for illustrative purposes only. STATEMENT OF THE INVENTION According, to the present invention there is provided a magnetic polymer composition for magnetic storage devices, comprising: 60-90% by weight of a polymer preferably vinyl-keto polymer and 10-40% by weight of transition metal based magneto-resistive alloys having magnetic properties. The magnetic polymer composition of the present invention is a synergistic composition, the ingredients of which are not reacting chemically but are interacting synergistically to produce unexpected results. The present composition is not a mere admixture. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 depicts the X-Ray diffractogram Figure 2 (a) to 2(d) depicts the magnetic measurement Figure 3 depicts the graph of Magnetization Vs. Temperature Figure 4 depicts the SEM micrographs of the subject composite Figure 5 depicts the magnetoresistance data DETAILED DESCRIPTION OF THE INVENTION. In the present invention, the transition metal based alloy and the vinyl-keto polymer are in the powder form and are weighed in the same ratio. In the process for the preparation of magnetic polymer composite, the magnetic alloy is added to the polymeric solution in a solvent and the mixed solution is thoroughly agitated for duration ranging from 5 to 30 minutes. The solution after thorough agitation is transferred into an open petri dish and the solvent evaporated under the influence of a magnetic field. This results in polymer coated alloys with preferred orientation, with dimensions as mentioned earlier and subsequent grinding gives oriented powder composites. In the method for preparing the magnetic polymer composite material of the present invention, the aforesaid vinyl-keto polymer can be effectively coated onto the alloys such as Cr-Fe Cr-Co, Cr-Ni, and the like. The choice of the solvent is an important criteria, as the polymer should not loose its identity in the chosen solvent. The kind of solvent to be used should be optionally selected depending on the kind of the polymer used. Before the agitation process a homogenous polymeric solution is ensured by tailoring the amount of polymer V/S solvent ratio. Coating the polymer on the magnetic alloy by using the thus prepared polymer solution is carried out by adding the magnetic alloy in the powdered form according to the calculated ratio of the alloy : polymer, followed by thorough agitation of the mixed solution of alloy and polymer in the said solvent for duration ranging from 10 to 30 minutes. Transferring the said mixed solution into an open vessel, where the magnetic polymer may be isolated in the form of cones, by orienting the magnetic-polymer particles under the influence of a magnetic field, during the course of evaporation of the solvent. Rapid evaporation of the polymeric solution results in a layer formation of the composite on the reaction vessel. These cones are carefully collected or scrapped or scooped from the surface of the said container. The said cones may be grounded thoroughly in a mortar-pestle to obtain the composite as a fine powder. The powder may be palletized using a 8-12 mm die; with an applied pressure of 4-6 tones. Resistivity, magnetic and Giant Magnetic Resistance measurement were carried out using a pellet of dimension 10,, x4.2mm. Detailed microscopic studies have been carried out using SEM/EPMA to inspect the microstructure and chemical homogeneity of alloy composite. In the subject process for the preparation of a magnetic polymer composite 10 -40 % by weight of the magnetic material (transition metal based alloy) and 60-90% by weight of the polymer having a repeating unit represented by the formula VKM is used. The said polymer has complete solubility in a said solvent. The method comprises of dissolution of the polymeric material in the said solvent and dispersing the magnetic transition metal based alloy using technique of sonication results in effective coating of the alloy particles with the layer of the polymeric material. The polymer coated transition metal based alloys are isolated in the form of cones having dimensions upto 2mm length and 0.5mm width. The magnetic and magneto resistive features of the coated composites have interesting features resembling that of the bulk alloys. The polymer coated transition metal based alloy core may be isolated by addition of an additive to improve on the conductivity behaviour of the said particles, electrically insulated as a result of polymeric coating. The dissolution and mixing of the polymeric material results in effective coating of the alloy particles. The direct evaporation of the solvent and subsequent grinding of the cones results in obtaining the composites in the powdered form. The important features observed is the magneto resistance feature is defined by the ratio, Delta R/Ro, showing 7.9 % at 299K for the composites. The composite in the form of cones have been isolated having the desired dimensions. The morphology of the cones using electron microscopic studies reveals spherical nature of the particles, coated with a uniform layer of the polymer. The process as herein before described and the evaporation of the solvent decides the topography/morphology of the polymer coated magnetic 'micro beads'. The average size of the spheres as obtained from the microscopic studies is 2.5 (am. The solvent used in the subject application is selected preferably from ethanol. The X-ray diffractogram of the Fe-Cr polymer as shown in figure 1, the Fe-Cr polymer is in the range of 20-70 at 20 degrees, using Co Kα as the source of the X-rays. The peaks in the range of 20-40 are indicative of the polymer reflections while those in the range of 45-65 are characteristics of the Fe-Cr alloy. The peak of highest intensity for the Fe-Cr alloy corresponds to the (110) reflection. The X-ray diffractogram of the alloy-polymer composite shows the characteristic reflections of both the alloy and the polymer. Figure 2(a-d) shows the plot of magnetization Vs Field of temperatures at 5K, 100K, 200K and 300K respectively. The saturation magnetization of the magnetic polymer decreases with increase in temperature. This systematic drop in the Ms value with increase in temperature is reflected in the plot of saturation magnetization Vs temperature as shown in figure 3, where the plot of Magnetization Vs Temperature value is observed to be linear. A systematic drop in the saturation magnetization value is observed with increase in temperature from 5K to 300K. The Scanning Electron Micrograph of the cone is shown in figure 4 (a) where the alloy and polymer were dissolved in ethanol and thorough agitation of the mixed solution was carried out for 10 minutes. The cones have been isolated as such by evaporating the mixed solution of the alloy-polymer in ethanol in the presence of magnetic field. The magnetic-polymer cones have dimensions up to 2mm in length and 0.5mm width. Figure 4(b) depicts the magnified view of the Scanning Electron Micrograph of the cone. The micrograph shows that all the particles are substantially spherical in shape. As a result of thorough agitation of the alloy-polymer solution, the Fe-Cr alloy particles are uniformly coated with a layer of the polymer. The average particle size of the polymer coated alloy particles is 2.5 to 5µm. Such spherical morphology of the coated particles is highly desirable for technological application. In the plot of resistivity as shown in figure 5, P Vs. Field, H in Tesla, a magneto- resistive ratio of the order of 7.9% is observed at high fields and at 299K. Such as observance of drop in MR ratio, especially at room temperature is highly desirable for commercial application of such magneto-resistive alloys. A negative sweep of the filed however shows an unusual drop on the resistivity value. The subject invention can better be understood with reference to the examples, which are for illustrative purposes and should not be construed to restrict the scope of the application. EXAMPLES Example 1: Fe-Cr alloy in the ratio of 74:26 of the mesh size of 150 and polyvinylpyrrolidone having average molecular weight of 40,000 was taken. The polymer was dissolved in 20ml of ethanol , taken as a solvent in a round bottom flask . On complete dissolution of the polymer, the said amount of the alloy is added to the clear polymer solution. The mixed solution is then allowed to undergo thorough agitation for 10 minutes, under ambient conditions. On completion of the process of agitation the solution is transferred into an open petri-dish and the solvent is allowed to evaporate under the influence of a magnetic field. The magnetic polymer is isolated in the form of oriented cones. Example 2: Fe-Cr alloy in the ratio of 70:30 of the mesh size of 150 and polyvinylpyrrolidone having average molecular weight of 40,000 was taken. The polymer was dissolved in 30ml of ethanol , taken as a solvent in a glass container. On complete dissolution of the polymer, the said amount of the alloy is added to the clear polymer solution. The mixed solution is then allowed to undergo sonication for 10 minutes, under ambient conditions. On completion of the process of sonication, the solution is transferred into an open container and the solvent is allowed to evaporate under the influence of a magnetic field. The magnetic polymer is isolated in the form of oriented cones, which are grounded in a mortar and pestle to obtain the said material in the powdered form. The said powder is then compacted in a 10mm die to get the pellets. The subject application is a mere statement of invention, where various modifications and alterations are possible without deviating from the scope of the invention, hence the present application should not be construed to restrict the scope of the invention. WE CLAIM:- 1. A magnetic polymer composition for magnetic storage devices, comprising: 60-90% by weight of a polymer preferably vinyl-keto polymer and 10-40% by weight of transition metal based magneto-resistive alloys having magnetic properties. 2. A composition as claimed in claim 1, wherein the said vinyl-keto polymer is polyvinyl pyrrolidone. 3. A composition as claimed in claim 1, wherein the said magneto-resistive alloys are selected from chromium-iron, chromium-cobalt or chromium-nickel. 4. A composition as claimed in claim 1, wherein the said polymer is in the form of powder. 5. A composition as claimed in claim 1, wherein the said magneto-resistive alloys are in the form of powder. 6. A process for the preparation of the magnetic polymer composition as claimed in claim 1, comprising: dissolving the 60-90% by weight of vinyl-keto polymer in a solvent as herein described by stirring the same in an open atmosphere at ambient temperature to obtain a clear, colourless solution; adding 10-40% by weight of magneto-resistive alloys in the said clear colourless solution; agitating the said clear, colourless solution at a frequency of 15-20 kHz for a period of 5-30 minutes, to get equally dispersed alloy in the said polymer solution; transferring the said polymer solution with equally dispersed said magneto-resistive alloys to the open non-metallic container on a magneto-stirrer allowing the said solvent to evaporate till the polymer coated transition metal based alloys are isolated in the form of cones from the said non-metallic container. 7. A process for the preparation of a composition as claimed in claim 6, wherein the said agitation is done in a sonicator. 8. A process for the preparation of a composition as claimed in claim 6, wherein the said non-metallic container is a glass container. 9. A process for the preparation of a composition as claimed in claim 6, wherein the said polymer coated transition metal based alloys isolated in the form of cones having dimensions upto 2mm length and 0.5mm width. 10. A process for the preparation of a composition as claimed in claim 6, wherein the said dissolution and mixing of the polymeric material results in effective coating of the said alloy particles. 11. A process for the preparation of a composition as claimed in claim 9, wherein the said composition isolated in the form of cones is grounded to form the powder. 12. A process for the preparation of a composition as claimed in claim 9, wherein the said composition isolated in the form of cones is grounded in mortar pestle. 13. A process for the preparation of a composition as claimed in claim 11, wherein the said powder is palletized in a 8-12 mm die by applying a pressure of 4-6 tones. 14. A process for the preparation of a magnetic polymer composition, substantially as herein before described with reference to the foregoing examples. 15. A magnetic polymer composition for magnetic storage devices, substantially as herein before described with reference to the foregoing examples.

Documents:

858-del-2000-abstract.pdf

858-del-2000-claims.pdf

858-del-2000-correspondence-others.pdf

858-del-2000-correspondence-po.pdf

858-del-2000-description (complete).pdf

858-del-2000-drawings.pdf

858-del-2000-form-1.pdf

858-del-2000-form-19.pdf

858-del-2000-form-2.pdf

858-del-2000-form-3.pdf

858-del-2000-gpa.pdf