Underlying causes of the magnetic behavior in surface patterned NiFe 2 O 4 thin films
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Research Letters
Underlying causes of the magnetic behavior in surface patterned NiFe2O4 thin films Goran Rasic, and Branislav Vlahovic, Department of Physics, North Carolina Central University, Durham, NC 27707, USA Justin Schwartz, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907, USA Address all correspondence to Goran Rasic at [email protected] (Received 10 May 2016; accepted 29 August 2016)
Abstract Surface patterned NiFe2O4 thin films exhibited large reduction in coercivity as compared with the films without surface patterning. Chemical analysis of the films revealed that there was no diffusion between the film and the substrate. Additional heating was shown to improve saturation magnetization without adverse effect on coercivity. The process of imprinting was eliminated as the possible cause of the phenomena as the flat stamp did not alter the magnetic properties of the film. Finally, it was shown that the orientation of the features with respect to the magnetic field does not have a significant effect on the magnetic response.
Introduction Ferrites are a special group of magnetic materials of particular technological interest due to their unique combination of ferromagnetism and large electrical resistance. One of the most important ferrites, nickel ferrite (NiFe2O4), a soft ferrimagnet with high-Curie temperature, relatively large saturation magnetization and high electrical resistivity, was the subject of this research. The combination of desirable properties makes NFO interesting for use in high-frequency[1,2] and spin filter devices,[3–5] sensors,[6] memory,[7–11] and magnetoelectric composites.[9,10,12–14] Traditionally, magnetic properties have been considered intrinsic and material dependent, so to change a magnetic property significantly, the composition must be altered. Recently, another approach was reported where control over one of the key magnetic properties, coercivity, is possible through proper nanostructuring of the thin film surface.[15–17] By patterning the surface with alternating parallel grooves we forced the magnetic domains walls to align along the edges of the features, creating an ‘artificial’ parallel stripe domain structure and reducing the coercivity. All of the initial experimental research, as well as theoretical investigations, supported this explanation of the results. If true, this would allow us to engineer the magnetic properties without changing composition. In combination with traditional methods of altering magnetic properties, such as doping and alloying, this would greatly add to the tunability of magnetic properties. More importantly, it would allow us to select materials based on other criteria (cost, strength, Curie temperature) and then tailor the magnetic properties for optimal performance. Before we can be certain that these findings are truly due to the surface patterning, however, there remain some unanswered questions. This paper focuses on the prominent questions
related to the observed coercivity reduction and pro
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