Methods of forming a magnetic memory cell are disclosed. The method comprises forming a magnetic cell core material over a substrate, wherein forming the magnetic cell core comprises forming a first magnetic region over the substrate, forming a tunnel barrier material over the first magnetic region, and forming a second magnetic region over the tunnel barrier material. A temperature of at least one of the substrate or a wafer stage underlying the substrate is maintained at a temperature below about 0° C. and the magnetic cell core material is exposed to at least a first beam comprising one of an ion beam or a neutral beam comprising ions or elements of at least one noble gas to remove portions of the magnetic cell core material. Related magnetic memory cells and methods of forming an array of memory cells are also disclosed.