Control of growth orientation in as-deposited epitaxial iron-rich nickel ferrite spinel

Abstract

The authors here report epitaxial growth of the ferrimagnet Ni x Fe 3-x O 4 (NFO) by atomic layer deposition at low temperatures. Films grow epitaxially at a reactor temperature of 250°C and require no further postannealing treatment. (100)-, (110)-, and (111)-oriented thin films of NFO are attainable by using MgO (100)/LaAlO 3 (100), LaAlO 3 (110), and Al 2 O 3 (001) substrates, respectively. This means that the direction of the easy axis of magnetization relative to the film surface can be selected by the choice of substrate. The authors carefully study nucleation onset and growth dynamics by varying the number of cycles used to deposit the films. This shows that the initial growth is mostly inhibited by the Fe-species, creating a small composition gradient for the first few nanometers of the film. The growth rate varies as a result of the choice of substrate, explained by the direction of the close packed layers in the film. The authors believe that the ability to deposit epitaxial ferrimagnetic films with angstrom thickness control at low temperatures will make a major impact on the possibility to grow multiferroic stacks and on low temperature monolithic device integration where a spontaneously magnetized sample is required.

A foundation for complex oxide electronics -low temperature perovskite epitaxy

“…This is an unexpected result, as multi-cation ALD films are very often amorphous and in need of post annealing to become crystalline due to the low deposition temperatures. Similar as-deposited epitaxy is recently shown for ferromagnetic NiFe 2 O 4 and antiferromagnetic NiTiO 3 as well as for LaMnO 3 [34][35][36] . LNO (100) is the most technologically interesting orientation for oxide electronics.…”

Effect of Subcycle Arrangement on Direct Epitaxy in ALD of LaNiO3

“…This very often leads to an amorphous potpourri of binary constituents that require postdeposition annealing to facilitate crystallization of a ternary compound. Note that some processes facilitate direct epitaxy by this approach, such as the growth of NiFe 2 O 4 , NiTiO 3 , LaMnO 3 , BaTiO 3 , and SrZrO 3 . − In multilayer deposition, binary films of some thickness (nanometer scale) are deposited and intermixing/diffusion takes place after deposition to create the ternary compound, usually aided by postdeposition annealing. An example of this is found in the deposition of epitaxial films of BiFeO 3 .…”