Hi,
Well the circuit you have posted has nowhere near enough gain to
detect the disturbances in the Earth's magnetic field, the gain
feedback resistor on your op-amps will not give you the required gain.
Have a look in the files section of the schematic i made a few Years
ago for the HMC1022, then take a look at my gain feedback resistors on
my op-amps, this will give you an idea of how much gain is needed.
Your 27k resistors will need to be higher in value.
I do not use this design anymore, i use a compass magnetometer now,
built it a few Weeks ago, getting better results with this design.
Hope this helps,

Mark