Low-remanence criterion for helicity-dependent all-optical magnetic switching in ferrimagnets

We demonstrate that a low-remanent sample magnetization M_R is crucial for all-optical magnetic switching (AOS) in ferrimagnets and ferrimagnet heterostructures. M_R may be devised by the composition of the material. However, it can also be controlled in situ by changing the sample temperature because it affects MR. We show that increasing the lattice temperature by laser pulses or a simple heating resistor enables AOS in a ferrimagnetic Tb-Fe film, which does not exhibit AOS at room temperature. We reconcile earlier contradicting results for AOS in heated and cooled magnetic films by applying the low-remanence criterion. It also applies to other existing rare-earth transition-metal (RE-TM) alloys, such as GdFeCo or Tb-Co, to ferrimagnet heterostructures, and to RE-free synthetic ferrimagnets.