I am developing an application that uses the magnetometer inside smart-phones to detect orientation w.r.t. the Earth's magnetic field.
I have noticed that when the phone is held close to a metal structure, such as Iron/Steel railings, there is a huge deflection in the magnetometer reading. There is no externally-induced current flowing through the structure; it has
induced warped the magnetic field by its own.
My question is, which types of metals can show this effect? Or more generally which type of elements can show this effect?
I suppose Ferromagnetic materials do show this effect. And paramagnetic materials (like Aluminium) will show a very weak effect. What about diamagnetic substances such as copper?
Update Changed the title to mention passively. I understand that a copper coil forced to carry current would induce a magnetic field that interferes with the Earth's magnetic field. But does the coil distort the Earth's magnetic field when no EMF is applied?