The embodiments herein relate to a magnetic field feedback based spintronic microwave oscillator driven by DC current. The microwave oscillator works based on a magnetic tunnel junction structure connected to a feedback waveguide. Any fluctuation in the magnetization direction of free magnetization layer of MTJ drives an oscillating current through the feedback waveguide which in turn exerts an oscillating magnetic field on the free layer and amplifies the magnetization fluctuations. If the DC current passing through the MTJ is more than a critical value, continuous processing states of the magnetization are possible. The critical current is independent of the thickness and magnetization of the free layer. A MTJ can be driven into spontaneous oscillations with DC current and magnetic field feedback circuit and can act as a spintronic microwave oscillator.