Mystery SOT-143 Part on Magnetometer
The voltage divider divides the 5 volts in half and makes what you have labeled as &quot;2.5 V&quot; as an analog reference so that your signal can swing positive and negative.  You might redraw your circuit showing this as your ground, and it might be easier to wrap your mind around it.  I believe the &quot;mystery part&quot; is a diode array, possibly a BAS4002A from the marking.  The idea is that the circuit will saturate the inductor in both directions from a symmetrical signal from the oscillator, but if a local magnetic field is aligned with the inductor core, it is added to the field produced by the coil in one direction (and subtracted in the other) so that it will not be saturated symmetrically. This will produce a bias on your integrator at R11.
Good luck!