FIELD OF THE INVENTION The present invention relates to a method for producing a transformer core formed of magnetic nano materials having very high saturation magnetic flux density and almost zero hysteresis loss. The invention further relates to an improved transformer with solid core formed of Fe70Co30 nanomaterials encapsulated with SiO2. BACKGROUND OF THE INVENTION It is known that a transformer is a device that transfers electrical energy from one circuit to another through inductively coupled coils. It works on the principle of electromagnetic induction. A varying alternating current applied in the primary winding of the transformer creates a varying magnetic flux in the transformer's core which in turn creates a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), in the secondary winding. Soft magnetic materials with low coercivity are major components of electromagnetic devices such as transformers, magnetic sensors, step motors, and magnetic recording heads. The miniaturization of such devices needs materials that can develop higher saturation magnetic flux density, so that the necessary flux densities can be obtained with reduced device dimensions, while simultaneously possessing a low coercivity. In conventional transformers, the primary and secondary coils are wound on the core, which is made of laminated grain oriented silicon steel. The magnetic flux density presently possible with these transformers is about 1.6 Tesla. Magnetic alloy materials, such as FePt, CoPt, FeCo and NiCo, have been widely studied because of their multiple functionalities as well as extensive applications [1-4]. FeCo is an intermetallic compound and it is a soft magnetic material with unique properties such as large permeability, low magnetostriction, high Curie temperature, small cohesive forces and largest saturation magnetization [5]. FeCo nanocrystals are building blocks of many magnetic materials and thin films [6-8]. They can also be used in biomedical systems [9]. Among the FeCo nanomaterials, it has been estimated that Fe70Co30 has the maximum saturation magnetic flux density. These nanomaterials are coated with SiO2 to prevent agglomeration of magnetic nanomaterials [10]. The non-patent literature published on 27.03.2007 entitled "structure and magnetic properties of FeCo-SiO2 nanocomposite synthesized by wet chemical method", by Xue gang Lu et al teaches a soft magnetic nanocomposite with FeCo particles encapsulated by amorphous SiO2 was synthesized using a co- precipitation combined H2 reduction method. The saturation magnetization of the (Fe70Co30)(SiO2)10 nanocomposite is as high as 200 emu/g, which is 4-5 times larger than that of traditional spinel ferrites. The frequency dependence of the complex initial permeability is intensely dependent upon the content of SiO2 insulating phase. With increasing the content of SiO2 to 10 wt.%, the cut-off frequency is drastically increased to over 1 GHz. The results show that a new high-frequency soft magnetic material with high saturation manetization (Ms) can be achieved by introducing FeCo/SiO2 nanocomposite. US2010040503 describes a soft magnetic alloy that in an FeCo nanocrystal soft magnetic material, exhibits a high saturation magnetic flux density of 1.85 T or more, and that ensures prolonged nozzle life and easy ribbon production; an amorphous alloy ribbon for use in production thereof; and magnetic parts utilizing the soft magnetic alloy. The soft magnetic alloy has the composition of the formula Fe100-x-y-aCoaCuxBy (in the formula, x, y and a each represent atomic % and satisfy the relationships 1