Effect of microstructure on magnetic properties and anisotropy distributions in Co/Pd thin films and nanostructures Justin M. Shaw, Hans T. Nembach, T. J. Silva, and Stephen E. Russek Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA Roy Geiss Materials Reliability Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA Christopher Jones and Noel Clark Department of Physics, University of Colorado, Boulder, Colorado 80309, USA Titus Leo and David J. Smith Department of Physics, Arizona State University, Tempe, Arizona 85287, USA Received 25 September 2009; published 19 November 2009 The structure of Co/Pd multilayers has a strong effect on the localized anisotropy distribution within a film and on the resulting switching properties of nanostructures fabricated from identical material. By varying the underlying seed layer in sputtered films, the microstructure can be controlled from being highly 111 textured to having a random grain orientation. We find a strong correlation between the lateral homogeneity of grain orientations and the localized anisotropy distribution in the material. X-ray diffraction and reflectivity indicate that the interface is better defined and more uniform in the textured case, consistent with the presence of a strong interfacelike anisotropy. DOI: 10.1103/PhysRevB.80.184419 PACS numbers: 75.75.+a, 75.50.Ss, 75.70.Cn, 75.30.Gw I. INTRODUCTION Perpendicularly magnetized nanostructures are central to many developing technologies including bit-patterned media BPM, 1 magnetic random access memory, 2 and spintronics devices. These technologies all rely on producing arrays of perpendicularly magnetized nanomagnets with predictable switching fields and narrow switching field distributions SFDs. An understanding of how to control and reduce SFDs is necessary before new technologies can utilize such perpendicular magnetic nanostructures. As an example, simulations of bit error rates in BPM were found to be highly dependent on anisotropy distributions, 3 which will likely have to be reduced below 5%. 4 Multilayered materials such as Co/Pd, Co/Pt, and Co/Ni are being explored for applica- tions in BPM Refs. 1 and 5–10 and spintronics 2 due to their highly tunable perpendicular anisotropy. While there are sev- eral factors that affect switching field distributions, such as lithographic variations and dipole interactions, 11 the domi- nant contribution in such materials resides in the intrinsic material properties. 12–14 More specifically, thin films, such as Co/Pd or Co/Pt multilayers, possess a lateral distribution of local anisotropy fields. When patterned into nanostructures, this distribution of anisotropy fields results in a distribution of nucleation fields from nanostructure to nanostructure. The origins of these local anisotropy fluctuations are not well understood but some evidence has suggested that variations in localized strain or grain crystal orientation may be responsible. 13–15 We have previously shown that we could dramatically change the SFDs in nominally identical Co/Pd multilayer structures by varying the seed layer. 13 That work concluded that variations in one or more material properties were domi- nating SFDs in the resulting nanostructures. However, we were unclear what specific properties were primarily respon- sible. In the present work, we show that the choice of the underlying seed layer strongly affects the resulting micro- structure, and then correlate the structure to the magnetic properties of the thin films and nanostructures. We present strong evidence that the grain orientation affects the local anisotropy field. II. EXPERIMENT Co/Pd multilayers were deposited by dc-magnetron sput- tering on thermally oxidized Si wafers with the following structure: seed layer/Cot Co  / Pd2.9t Co   8 / Pd3 nm, where t Co is the individual Co layer thickness. The seed layer was either a single Pd3 nm layer or a Ta3 nm/Pd3 nm bilayer. These seed layers will be referred to as the Pd seed and the Ta seed, respectively. Film deposition rates were cali- brated by use of a profilometer that was itself first calibrated to within 5% of a standard. The magnetic properties of the resulting thin films were characterized using a superconduct- ing quantum interference device SQUID magnetometer that was calibrated using a NIST traceable Ni sphere stan- dard and an alternating gradient magnetometer. Nanostructures were fabricated using electron-beam li- thography to expose a polymethylmethacrylate layer which was developed in methyl isobutyl ketone MIBK: isopropanol 1:3. Approximately 20 nm of ion-beam-deposited Cr was then lifted off to form an etch mask. The patterned etch mask was then transferred to the Co/Pd multilayer thin films via a 300 eV Ar ion mill. Figure 1a shows a scanning electron microscope SEM image of typical nanostructures resulting from this process. PHYSICAL REVIEW B 80, 184419 2009 1098-0121/2009/8018/1844198 ©2009 The American Physical Society 184419-1