Building a variable frequency magnetic pulser
The coil, it seems, is not well-defined and my first thought is that an op-amp won't cut the mustard on driving it successfully. The LM301 is only really suitable for driving kohm loads so I believe you ought to invest in a power transistor to interface the op-amp to the solenoid/coil.

But hold-on, lose the op-amp and use a logic level mosfet driven from the PIC'c PWM output. Connect source to 0V, gate to the PIC output and put the coil between drain and positive supply. This will give you a better drive to the coil and don't forget to put the diode across the coil reverse biased to catch the back emfs when the transistor is turned off: -



The 100k resistor is to ensure the mosfet remains off when the input is not connected to anything (important). The 1k is to limit stress on the PIC output because the MOSFET will likely have input capacitance in the order of 1nF. You need to find a MOSFET that will switch fully on with the positive drive level from the PIC (5V presumably).