You'll need to be a bit more specific about what you are asking. All living things generate electromagnetic fields. More complex organisms like mammals can generate numerous fields from various tissues. The gut for instance, produces a range of low frequency fields as muscular peristalsis moves food through. Other species have specialized organs that can generate/detect electric fields that can be used for sensing (lots of fish). Some can even generate such large fields that they can use an electric discharge as a weapon (electric eel). Some folks in my lab have measured various magnetic fields in animals using SQuID magnetometers. We also look at action potential propagation through tissues using the fluorescence of voltage sensitive dyes. There are most likely thousands of papers that discuss some aspect of electromagnetism in animals so it would be best to narrow it down a bit.
You'll need to be a bit more specific about what you are asking. All living things generate electromagnetic fields. More complex organisms like mammals can generate numerous fields from various tissues. The gut for instance, produces a range of low frequency fields as muscular peristalsis moves food through. Other species have specialized organs that can generate/detect electric fields that can be used for sensing (lots of fish). Some can even generate such large fields that they can use an electric discharge as a weapon (electric eel). Some folks in my lab have measured various magnetic fields in animals using SQuID magnetometers. We also look at action potential propagation through tissues using the fluorescence of voltage sensitive dyes. There are most likely thousands of papers that discuss some aspect of electromagnetism in animals so it would be best to narrow it down a bit.