Magnetic stimulation using micro-coils has shown to be an effective method for brain neural modulation [1]. These micro-coils could arguably be superior to commonly used micro-electrodes in terms of long-term functionality. This is because, unlike electrode based devices, magnetic coils do not need to have direct contact with brain tissues and thus their efficiency and stimulation capability do not degrade overtime. In this study, we compare three different micro-coils and show that the use of magnetic-core in the inductors could substantially improve the coil's performance and help to generate more than 13 times stronger electric field and electric field gradient.