Title of Invention

A NOVEL COMPOUND EXHIBITING MAGNETOELECTRIC COUPLING AND HIGH DIELECTRIC CONSTANT AT ROOM TEMPERATURE

Abstract

Title : Novel compound exhibiting magnetoelectric coupling and high dielectric constant at room temperature ABSTRACT The present invention relates to novel compounds exhibiting magnetoelectric coupling and high dielectric constant at room temperature having formula Bi0.9-XRxLa0.1 Fe03 wherein R is a Lanthanide element such as Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and the value of x is between 0.01 to 0.2. Such compounds exhibit co-existence of ferroelectric and magnetic ordering at room temperature along with large dielectric constant and have wide applications in non-volatile memory devices, dynamic random access memories, magnetic sensors, dielectric anamoly near magnetic transition actuators and the like. The high dielectric constant of the material is useful for microwave applications, capacitors and similar applications.

Full Text

FORM2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See section 10; rule 13) 1. TITLE OF INVENTION A NOVEL COMPOUND EXHIBITING MAGNETOELECTRIC COUPLING AND HIGH DIELECTRIC CONSTANT AT ROOM TEMPERATURE 2. fata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005. State of Maharashtra, India, an aided autonomous institution under the administrative purview of Atomic Energy, Government of India. The following specification particularly describes the nature of this invention and the manner in which it is to be performed. Field of invention The present invention relates to novel compound of formula I that exhibits magnetoelectric coupling and high dielectric constant at room temperature, said formula being Bi0.9-xRxLao.1 Fe03 Formula I wherein, R is a Lanthanide element such as Gadolinium (Gd), Terbium (Tb), . Dysprosium (Dy), Holmium (Ho), Erbium (Er). The compounds of formula I have wide applications in non-volatile memory devices, dynamic random access memories, magnetic sensors, actuators and the like. The high dielectric constant of the material is useful for microwave applications, capacitors and similar applications. This application has been divided out from patent application No. 409/MUM/2003 dated April 24, 2003.. Background of the invention * Magnetoelectric are materials which exhibit coexistence of magnetic and ferroelectric ordering at a certain temperature range. Using such compounds, spontaneous magnetization can be switched by applying a magnetic field and spontaneous electric polarization can be switched by applying electric field. Often some coupling between the two is also achieved. However, there are very few such compounds existing in nature or has been synthesized in the laboratory. Moreover, for magnetism, the presence of transition metal a electrons in the element is essential, but they reduce the tendency for off-center ferroelectric distortion. Consequently, additional electric or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously. Although a few systems exhibiting both ferromagnetism and ferroelectricity have been found so far, their use in device applications has not been successful mainly due to the reason that most of such systems have Neel or Currie temperature below room temperature and thus exhibit magnetoelectric effect at low temperature making it difficult for device applications. In order to overcome this problem, composites of ferroelectric magnetic materials have been developed which have transition temperatures above room temperature. However, realization of such composites is a very complex process since the magnitude and sign of the effective magnetoelectric coupling depends on the treatment of the composite and even slight variations in the process parameters leads to appreciable variations in the end properties of such complexes. Thus, it is very difficult to achieve the desired properties. Thus, there is a need of materials, which exhibit magnetoelectric coupling at room temperature with chemical homogeneity and consistent properties of the materials. Objects of the invention Thus the object of the present invention is to provide compounds exhibiting co-existence of ferroelectric and magnetic ordering at room temperature. Another object of the present invention is to provide compounds exhibiting such magnetoelectric coupling at room temperature and having high dielectric constant. Yet another object of the present invention is to provide compounds which are chemically homogeneous thereby ensuring consistent properties. A further object of the present invention is to provide a process for manufacture of compounds exhibiting magnetoelectric coupling at room temperature. Summary of the invention Thus, according to one aspect of the invention there is provided novel compound of formula I exhibiting magnetoelectric coupling and high dielectric constant at room temperature having formula: Bio9-xRxLa01Fe03 Formula I wherein, R is a Lanthanide element such as Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and the value of x is between 0.01 to 0.5. Detailed description The novel compound of formula I show simultaneous ferroelectric and magnetic ordering and high dielectric constant at room temperature. It helps to bring the effect in a single material which otherwise requires use of hetero-structures or composites of ferroelectric and magnetic materials. R is Lanthanide element such as Gd, Tb, Dy, Ho, Er having large magnetic moment and ionic radius similar to that of Bismuth (Bi). A preferred selection of R is Tb so that the compound has the formula Bio,9-xTbxLao.1Fe03, being formula II. The preferred value of x is between 0.01 and 0.5, more preferably between 0.01 to 0.2, most preferably between 0.01 to 0.125, most preferred value being 0.075 so that the preferred compound becomes Bi0.82525Tb0,075La0.1Fe03 of formula III. The compound exhibits saturated ferroelectric hysteresis loop at room temperature. The ferroelectric transition temperature Tc is 805±5°C. The compound shows large magnetic moment and has a magnetic transition temperature TM of the order of 250±2°C. The compound shows dielectric constant as large as 4000 at 10 kHz at room temperature. There is also increase in saturation polarization (Ps) from 0.051 uC/cm2to 0.307 uC/cm2 and remnant polarization (Pr) from 0.03 uC/cm2to 0.204 uC/cm2of the compound after magnetic poling with the field of 1 Tesla. With further increase in poling field to 5 Tesla, Ps & Pr values enhance to 0.404 and 0.291 uC/cm2 respectively (Fig. 2-4). It also exhibits increase in dielectric constant with increase in applied magnetic field, which indicates presence of magnetoelectric coupling in the compound. The compound of formula I can be in the form of thin film, fine particles or single crystal. The process of manufacture of the compound of the present invention will now be demonstrated and the product tested with reference to non-limiting examples. Examples Example 1: Process for manufacture of compound of formula III Bi0.825TD0.075La0.1 Fe03. Bismuth oxide (Bi203), Terbium oxide (Tb407), La acetate (La(C2H302)3. 1.5 H20), and Ferric ammonium sulphate (NH4Fe(S04)2. 12 H20) were weighed in stoichiometric proportions. The specific weights of the starting compounds are given below. Bismuth oxide (Bi203) - 3.9607 gm Terbium oxide (Tb407) - 0.2804 gm La acetate (La(C2H302)3. 1.5 H20) - 0.6807 gm Ferric ammonium sulphate (NH4Fe(S04)2. 12 H20) - 9.6438 gm Bi203 and Tb407 were dissolved in minimum quantity of conc HNO3. La acetate and Ferric ammonium sulphate were dissolved in deionized water. All solutions were mixed and diluted to 500 ml using deionized water. Concentrated NaOH solution prepared in deionized water, was added to the solution to co-precipitate all the cations as hydroxides. The pH of the solution during precipitation was maintained at 9. The precipitate was then filtered, washed with deionized water and dried. It was calcined to get the reacted material. The calcination was carried out at 500°C for 1 hour. The reacted powder was compressed into pellets using hydraulic press. The pellets were further sintered at 800°C for 1 hour in the furnace. The sample so obtained was used for the experiments described hereinafter. A sample (comparative sample) of known compound having formula Bi0.9La0.1Fe03 was prepared by similar method and used for comparative studies. Various physical, electrical and other properties of the compound of formula III were tested and the results are provided in the figures of the accompanying drawings, in which Figures 1(a) and 1(b) show differential thermal analysis (DTA) curve for sample of example 1. Figure 2 shows ferroelectric hysteresis loop for sample of example 1. Figure 3 shows ferroelectric hysteresis loop for sample of example 1 poled in magnetic field of 1 Tesla. Figure 4 shows ferroelectric hysteresis loop for sample of example 1 poled in magnetic field of 5 Tesla. Figure 5 shows Magnetization - field (M-H) curve obtained at room temperature for sample of examples 1 and comparative sample. Figure 6 shows the set-up for measuring capacitance of sample of example 1. Figure 7 shows Dielectric Constant, Epsilon (e) vs. applied magnetic field for sample of example 1. Example 2: Experiment for determining magnetic transition temperature (TM) and ferroelectric transition temperature (Tc) Differential thermal analysis study was carried out on the sample of example 1. The sample used for analysis was calcined at 800°C for 1 hour. The graph obtained by plotting Heat Flow against Temperature is illustrated in Figures 1(a) and 1(b). The peak obtained in Figure 1(a) at around 240°C indicates the magnetic transition temperature (TM) and the peak obtained in Figure 1(b) at around 805°C indicates ferroelectric transition temperature (Tc). This confirms the presence of the co-existence of magnetic and ferroelectric ordering in the sample at room temperature. Example 3: Experiment for obtaining hysteresis loop for sample of example 1. Sample of example 1, sintered at 800°C for 1 hour in the form of pellet having diameter around 1 cm and thickness of around 0.2 cm, was used to study ferroelectric properties. The ferroelectric hysteresis loop for the sample was obtained and is illustrated in Figure 2. The saturated ferroelectric hysteresis loop has saturation polarization (Ps) and remnant polarization (Pr) values of 0.051 and 0.03 |iC/cm2 respectively. Example 4: Experiment for obtaining hysteresis loop of sample of example 1 poled in magnetic field of 1 Tesla. The sample of example 1, sintered at 800°C for 1 hour in the form of pellet having diameter around 1 cm and thickness of around 0.2 cm, poled in magnetic field of 1 Tesla was used to study ferroelectric properties. The ferrolelctric loop obtained on the sample is illustrated in Figure 3. The saturated hysteresis loop has saturation polarization (Ps) and remnant polarization (Pr) values of 0.307 and 0.204 μC/cm2 respectively. Enhancement in the values of saturation polarization and remnant polarization is observed for the sample when poled in the presence of magnetic field. Example 5: Experiment for obtaining hysteresis loop of sample of exampJe 1 poled in magnetic field of 5 Tesla. The sample of example 1, sintered at 800°C for 1 hour in the form of pellet having diameter around 1 cm and thickness of around 0.2 cm, poled in magnetic field of 5 Tesla was used to study ferroelectric properties. The ferroelectric loop obtained on the sample is illustrated in Figure 4. The saturated hysteresis loop has saturation polarization (Ps) and remnant polarization (Pr) values of 0.404 and 0.291 μC/cm2 respectively. Enhancement in the values of saturation polarization and remnant polarization is observed for the sample when poled in the presence of higher magnetic field. Example 6: Experiment for obtaining M-H curve for sample of example 1 and comparative sample. Sample of example 1 and the comparative sample were heated at 800°C for 1 hour. M-H curve was obtained for both the sample at room temperature by using SQUID magnetometer. The curve is demonstrated in Figure 5. The curve shows enhancement in magnetization for sample of example 1 in comparison to the comparative sample. Example 7: Experiment for obtaining capacitance vs. applied magnetic field for sample of example 1. Sample of example 1 was heated at 800°C for 1 hour. The variation in capacitance of the sample with increase in magnetic field was observed. The capacitance was measured by using LCR-bridge in presence of the magnetic field. Figure 6 shows the set-up used for measurement. The sample (1) was placed in between two ferromagnetic material (2) and magnetic field was applied. The variation of capacitance with magnetic field is illustrated in Figure 7. Measurements were carried out at frequencies ranging between 10 KHz and 1 MHz. The graph obtained shows linear increase in capacitance with increase in applied magnetic field. Advantages The compounds of the present invention exhibit co-existence of ferroelectric and magnetic ordering at room temperature along with large dielectric constant. The compounds exhibit saturated ferroelectric hysteresis at room temperature. The compounds possess large magnetic moment and dielectric constant of 4000 at 10 kHz at room temperature. There is increase in saturation polarization after magnetic poling of the compounds. The compounds also show increase in dielectric constant with increase in applied magnetic field. The compounds replaces complex composite or hetero-structures of ferroelectric and magnetic materials as it is easier to fabricate devices with single compounds rather than composites. The compounds will find various applications in ferroelectric and magnetic devices. There is additional degree of freedom since polarization can be brought about by either electric or magnetic field. Thus, by combining alternative and direct magnetic and electric fields, more complex devices may be integrated. Magnetoelectric coupling can be used in magnetic sensors, actuators and read and write memory devices. We claim: 1. Novel compound of formula I exhibiting magnetoelectric coupling and high dielectric constant at room temperature having formulae: Bi0,9.-xRxLa0.1Fe03 Formula I wherein R is a Lanthanide element such as Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and the value of x is between 0.01 to 0.5. 2. Compound according to claim 1, wherein x is preferably between 0.01 and 0.2 3. Compound according to claim 2, wherein x is preferably 0.075. 4. Compound according to claim 1, wherein R is Tb. 5. Compound according to claims 1 or 4, wherein R is Tb and x is 0.075 so that the compound of formula I is Bi0.825Tb0.075La0.1Fe03. 6. Compound according to claim 1, wherein compound of formula I has ferroelectric transition temperature of around 805±5°C. 7. Compound according to claim 1, wherein compound of formula I has magnetic transition temperature of around 250+2°C. 8. Compound according to claim 1, wherein compound of formula I has saturation polarization and remnant polarization values of 0.051 and 0.03 μC/cm2, respectively. 9. Compound according to claim 1, wherein compound of formula I has saturation polarization and remnant polarization values of 0.307 and 0.204 μC/cm2, respectively, in magnetic field of 1 Tesla. 10. Compound according to claim 1, wherein compound of formula I has saturation polarization and remnant polarization values of 0.404 and 0.291, μC/cm2, respectively, in magnetic field of 5 Tesla. 11. Compound of formula I as described herein in the text, examples and accompanying drawings. Dated this 1st day of June 2004

Documents:

623-mum-2004-abstract(4-6-2004).doc

623-mum-2004-abstract(4-6-2004).pdf

623-mum-2004-cancelled pages(4-6-2004).pdf

623-mum-2004-claims(granted)-(4-6-2004).doc

623-mum-2004-claims(granted)-(4-6-2004).pdf

623-MUM-2004-CORRESPONDENCE(12-9-2008).pdf

623-mum-2004-correspondence(14-3-2008).pdf

623-MUM-2004-CORRESPONDENCE(29-9-2008).pdf

623-mum-2004-correspondence(ipo)-(10-11-2008).pdf

623-mum-2004-drawing(4-6-2004).pdf

623-mum-2004-form 1(4-6-2004).pdf

623-mum-2004-form 19(21-6-2004).pdf

623-mum-2004-form 2(granted)-(4-6-2004).doc

623-mum-2004-form 2(granted)-(4-6-2004).pdf

623-mum-2004-form 3(4-6-2004).pdf

623-mum-2004-form 5(4-6-2004).pdf

623-mum-2004-power of attorney(4-6-2004).pdf

623-mum-2004-power of attorney(6-9-2004).pdf

abstract1.jpg