No abstract

In this study, we report on a shape-imposed magnetic anisotropy in micro-and nanostructures defined in antiferromagnetic (AF) LaFeO3 (LFO) thin films. Two distinct types of structures are investigated; embedded magnets created via ion implantation, and free-standing magnets created via ion milling. Using a combination of x-ray photoemission electron microscopy and x-ray absorption spectroscopy, we examine the impact of structure type, AF layer thickness, and crystal geometry on the Néel vector orientation in these structures. We demonstrate a distinct shape-imposed anisotropy in embedded and free-standing structures alike, and show that both parallel and perpendicular alignment of the AF spin axis with respect to structure edges can be achieved by variation of the AF layer thickness and the orientation of the structure edges with respect to the LFO crystalline axes. This work demonstrates how fabrication procedure affects the magnetic order in thin film AF nanostructures and shows how nanoscale patterning can be used to control the orientation of the Néel vector in epitaxial oxide thin films.

In this study, we report on the magnetic domain formation in ultrathin blanket films and patterned micro-and nanostructures of ferromagnetic (FM) La 0.7 Sr 0.3 MnO 3 single-layers and antiferromagnetic (AF)/ferromagnetic LaFeO 3 /La 0.7 Sr 0.3 MnO 3 bilayers, as investigated by soft x-ray photoemission electron microscopy. In single-layer La 0.7 Sr 0.3 MnO 3 , the domain size is significantly reduced compared to that found in thicker layers, and rectangular micromagnets display metastable multidomain states distinctly different from the flux-closure ground states commonly found in thicker elements. In the LaFeO 3 /La 0.7 Sr 0.3 MnO 3 bilayers, complex multidomain patterns are observed for blanket films and patterned magnets with robust perpendicular (spin-flop) coupling between spins in the AF and FM layers. By thermal cycling of the sample through the La 0.7 Sr 0.3 MnO 3 Curie temperature, we find that the native antiferromagnetic domain pattern of LaFeO 3 pins the location of domain boundaries in the adjacent La 0.7 Sr 0.3 MnO 3 layer.

Exchange bias occurs in field-cooled antiferromagnet/ferromagnet systems and can most often be explained in terms of uncompensated magnetic moments at the interface, that are pinned in their orientation during field-cooling. The presence of spin-flop coupling is often associated with spincompensated interfaces. Here, we report exchange bias in complex oxide heterostructures of antiferromagnetic LaFeO 3 and thin layers of ferromagnetic La 0.7 Sr 0.3 MnO 3 with several intriguing features. The exchange bias does not require field cooling but can also be obtained by applying a setting field at elevated temperature. Furthermore, the exchange bias is positive for setting fields up to 3 T, and its magnitude is strongly dependent on the setting field strength. X-ray magnetic linear dichroism measurements show a predominantly perpendicular spin configuration at the interface. We discuss the possibility of the exchange bias being driven by a net moment from spin canting in the antiferromagnet due to Dzyaloshinkii-Moriya interactions.

Magnetic metamaterials such as artificial spin ice offer a route to tailor magnetic properties. Such materials can be fabricated by lithographically defining arrays of nanoscale magnetic islands. The magnetostatic interactions between the elements are influenced by their shape and geometric arrangement and can lead to long-range ordering. We demonstrate how the magnetic order in a two-dimensional periodic array of circular disks is controlled by the lattice symmetry. Antiferromagnetic and ferromagnetic order extending through the entire array is observed for the square and hexagonal lattice, respectively. Furthermore, we show that a minute deviation from perfect circularity of the elements along a preferred direction results in room-temperature blocking and favors collinear spin textures.