Electrophysiology and the magnetic sense: a guide to best practice.

Magnetoreception, sensing the Earth's magnetic field, is used by many species in orientation and navigation. While this is established on the behavioural level, there is a severe lack in knowledge on the underlying neuronal mechanisms of this sense. A powerful technique to study the neuronal processing of magnetic cues is electrophysiology but, thus far, few studies have adopted this technique. Why is this the case? A fundamental problem is the introduction of electromagnetic noise (induction) caused by the magnetic stimuli, within electrophysiological recordings which, if too large, prevents feasible separation of neuronal signals from the induction artefacts. Here, we address the concerns surrounding the use of electromagnetic coils within electrophysiology experiments and assess whether these would prevent viable electrophysiological recordings within a generated magnetic field. We present calculations of the induced voltages in typical experimental situations and compare them against the neuronal signals measured with different electrophysiological techniques. Finally, we provide guidelines that should help limit and account for possible induction artefacts. In conclusion, if great care is taken, viable electrophysiological recordings from magnetoreceptive cells are achievable and promise to provide new insights on the neuronal basis of the magnetic sense.

Evidence of magneto-structural coupling affecting magnetic anisotropy in a cobalt nano-composite.

By investigating temperature dependent structural and magnetic properties of cobalt (Co) embedded within nanoporous anodized alumina template, we observe changes in the easy axis of Co magnetization and an unusual increase in its saturation magnetization below a temperature T cr. Analysis of our M(H) data reveals that the magnetized volume of the sample increases rapidly as T falls below T cr. To understand these features we perform micro-magnetic simulations for a single Co-nanopillar wherein by varying its magneto-crystalline anisotropy energy we are able to show that the changes observed near T cr are related to the changes in the magnetic anisotropy of the nanopillar. We propose crystallographic structural distortions trigger changes in the balance between shape and magneto-crystalline anisotropy in our nanopillar. Our results suggest interplay between magnetism, structure and magnetic anisotropy in low dimensional Co-nanopillars, which can be modified with temperature of the system.