Dr. Kotnala has diversified research experience in the field of electronic and magnetic materials, magnetic measurements, solar cell, hydroelectric cell, spintronics, ferrites etc. He has delivered a lot of significant work to society, industry, and the environment.
Dr. Kotnala has invented a green energy device named “Hydroelectric Cell” based on ferrites and non-magnetic oxide materials, which generates electricity using water only. This water-running cell can be used to energize laptop, torch, mobile phones etc., and is eco-friendly. This cell is a unique invention in the field of green energy. In the reverse mode of the cell i.e. by applying external power, the cell can be used to generate its by-products hydrogen and zinc hydroxide in large amounts for industrial applications.
Dr Kotnala has got 12 years of experience in the research of solar cell to develop low-cost fabrication technology. A process of fabrication of P ± NN + silicon solar cells by simultaneous diffusion of boron and phosphorous into N-type silicon through a thermally grown silicon dioxide layer of 0.1 micron thickness was the main work of Dr. Kotnala during his doctorate (PhD). The process was well suited for large-scale production of back surface field silicon solar cell. This work was published in “ASSET” United National University publication as “Low Cost Process – Solar Cell”. To enhance the efficiency of solar cell some new initiatives were undertaken by him. The developed technology was given to Central Electronics Ltd in 1988. Dr. Kotnala’s remarkable contribution to Solar Cell is very important and distinct. He wrote a popular book on the solar cell in 1986 cherished by readers even today. Many research papers were also published by him on the solar cell. In 2012, 100 KW solar cell panels were planned & got erected at EQDC Gandhi Nagar in the capacity a Governing Body member of EQDC. Currently, he is a key member of the solar cell project of the Ministry of new and renewable energy (MNRE).
A highly humidity sensitive oxygen deficient porous magnesium ferrite was developed and its conduction mechanism by physisorbed water layers was established experimentally & theoretically through isosteric heat of adsorption and binding energy of water molecules. Further, oxygen deficient porous magnesium ferrite thin films were developed by Pulse Laser Deposition (PLD), showing Colossal Humido-Resistance (CHR) change with humidity, ideal for device application.
Magnetic materials and magnetism is the heart of his scientific career. In fact, the idea of Hydroelectric Cell originated while working on magnesium ferrite as a humidity sensor. Dr. Kotnala has been working on ferrites since 1991 and started synthesizing hard ferrite thin films for magneto-optical properties. His experience in ferrites covers hard to almost all soft ferrites. Lithium ferrite, Bismuth ferrite, Barium ferrite etc were designed & developed in his lab for microwave applications.
For the first time in his lab, improved electromagnetic interference shielding response was established in Polyaniline coated fabrics by substituting dielectric and magnetic nanoparticles of BaTiO3 (15 nm) or Fe3O4 (40 nm) within coated polyaniline (PANI) matrix. The high value of absorption-dominated SET (97 % attenuation) and specific shielding effectiveness value of 18 dB cm3/g were achieved.
He applied his rich knowledge and experience in ferrites to the emerging multiferroic and spintronics field. In multiferroics, ferromagnetism was induced in non-magnetic ferroelectric barium titanate by chromium doping. Induced electric polarization was obtained by applying an external magnetic field due to the local interaction of d electron spins with disordered electric dipoles via oxygen vacancies created by Cr doping in BaTiO3. In order to observe enhanced magneto-electric coupling, bilayer and trilayer thin films of BiFeO3/BaTiO3 were grown by in-house RF sputtering techniques. Office of Naval Research (ONR), Washington, USA had entrusted work on multiferroics for development of electromagnetic sensor with Italy group and awarded US$ 0.105 million as a contract project in 2010.
Spin-Hall Effect is used for spintronic devices, magnetic memory, spin logic gates, nano sized microwave signal generator and single electron transistor applications. In the lab, Colossal magneto-resistive materials like Sr2FeMoO6 and La1-xPbxMnO6 were explored for spintronic applications. Sr2FeMoO6 (SFMO) is a 100% spin-polarized, half-metallic compound. It exhibits high Curie temperature (>400 K) and excellent magneto-resistance properties at low field, making it a very promising candidate for Magnetic Tunnel Junction (MTJs). Tri-layer of SFMO/SrTiO3/SFMO structure on STO buffered Si (100) substrate were fabricated by pulsed laser deposition (PLD) technique for MTJ. The TMR value ~7% at room temperature was attributed to spin-dependent tunneling across a uniform ultra-thin STO tunnel barrier sandwiched between two identical SFMO electrodes. Room Temperature Metal-Insulator transition was observed in Pb substituted Lanthanum Magnetite.
The influence of perpendicular magnetic anisotropic Co/Pt bilayer due to weak spin pumping was investigated on ferromagnetic resonance signal for the first time in India by Dr. Kotnala. Bilayer paramagnetic and ferromagnetic thin film Pt/FeSi 3% were fabricated for microwave nano oscillator device application.
Dr. Kotnala established the Magnetic Measurement Standards Laboratory at International level in CSIR-NPL in 1998 and on Jan 8, 2012, this laboratory was internationally recognized for 10 magnetic measurements parameters in the preview of ISO: 17025 for the International Bureau of Weights & Measure, (BIPM) France. The laboratory is currently dedicated to primary standards on magnetic measurements and Industrial consultancy. Dr. Kotnala gave consultancy to nine big industrial houses & PSUs for solving magnetic materials & measurements related complex problems. He also planned & guided to establish a laboratory for Advanced Anechoic EMI/EMC testing at EQDC Gandhi Nagar (Gujarat Govt.). Being an active governing body member a lot of other activities related to ISO: 17025 standards were supported for EQDC by Dr. Kotnala.