Inductors and transformers are electrical devices critical to power conversion systems. The current-voltage (I-V) behavior of these devices is very nonlinear as a result of the magnetic cores used in their construction. However, in the design of these power conversion systems the present state of Spice-based models is limited to low frequency and room temperature effects. An addition to the present model found in many Spice type environments, Jiles-Atherton, is the subject of this work. Chapter 1 of this dissertation introduces the source of these nonlinearities as being a result of the relationship between the magnetic flux density, B, and the applied magnetic field, H. Chapter two then derives the original mathematical model used in the Spice, Jiles-Atherton, to provide a physical basis of the addition to the model. The original derivation as it can be found in the referenced literature shows that a temperature and frequency dependence on the model does not exist. This work will seek to add such a dependence on temperature first followed by frequency. Using this approach, the temperature dependence can be modeled without the core experiencing self-heating. The model therefore must be capable of being further modified after the temperature dependence is added.