Lining Up for New High-Density Memory Devices

Newswise — The Science

To reduce the size and increase the durability of computers, cell phones, and other data-storing devices, scientists designed a structure made of tiny layers, which resembles a thick chessboard butcher-block table. Using the material, where each layer is made of one of two composites, scientists can vertically manipulate the magnetization, enabling a type of magnetic coupling between two layers commonly employed in magnetic devices. They can “pin,” or set, the magnetic states of the materials at their unique states of maximum sensitivity; this setting is essential for magnetic device stability.

The Impact

Extremely thin layers of a unique material could lead to the design of new read heads for hard drives and other high-density memory devices that have greater stability when exposed to high temperatures and a smaller size.

Summary

Scientists grew a vertically aligned nanocomposites lattice matched on a SrTiO₃ (STO) substrate using laser deposition. These micrometer-thick layers exhibited strong, perpendicular (vertical) magnetic coupling (exchange bias). The degree of structural strain in the nanocomposites effects the magnetic exchange bias behavior (that is, a type of magnetic coupling between two layers commonly employed in magnetic devices). In addition, the composition of the different layers in the film (La_0.7Sr_0.3MnO₃ [LSMO] and BiFeO₃ [BFO]) determines the density, degree of strain accommodation, and magnetic phase transition, which all affect the overall magnetic exchange bias coupling strength. By controlling the composition of the layers in the nanocomposites, scientists can tune the degree of magnetic exchange bias coupling strength. The research team conducted a microstructural analysis of the nanocomposite films using transmission electron microscopy and scanning transmission electron microscopy. The images show vertical structures with boundaries. They measured the magnetization of the nanocomposites using a magnetometer. This new nanoscale architecture can be used for data storage in high-density memory devices as an alternative to conventional, in-plane magnetic exchange bias; such devices could provide more efficient performance.

Funding

This work was supported by the U.S. National Science Foundation (NSF)-Ceramic Program, DMR-1401266 (Texas A&M) and DMR-1643911 (Purdue, for vertically aligned nanocomposite design and growth) and DMR-0846504 (for high-resolution scanning transmission electron microscopy analysis). Sandia National Laboratories (Sandia) is a multi-program laboratory, managed and operated by Sandia Corporation (a wholly owned subsidiary of Lockheed Martin Corporation) for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy (DOE), under contract DE-AC04-94AL85000. The work at Los Alamos National Laboratory (LANL) was partially supported by the Laboratory Directed Research and Development (LDRD) program and was performed, in part, at the Center for Integrated Nanotechnologies (CINT), a DOE Office of Science user facility. J. L. MacManus-Driscoll gratefully acknowledges support from the European Research Council (ERC-2009-AdG 247276 NOVOX). A portion of the electron microscopy experiment work was performed at the National Center for Electron Microscopy (NCEM), which is supported by DOE’s Office of Science, Office of Basic Energy Sciences, under contract DE-AC02-05CH11231. J. Jian and W. R. Zhang are grateful to Drs. Peter Ercius, Jim Ciston, and Chengyu Song for additional help and fruitful discussions at NCEM.

Publications

W. R. Zhang, A. P. Chen, J. Jian, Y. Y. Zhu, L. Chen, P. Lu, Q. X. Jia, J. L. MacManus-Driscoll, X. H. Zhang, and H. Y. Wang, “Strong perpendicular exchange bias in epitaxial La_0.7Sr_0.3MnO₃:BiFeO₃ nanocomposite films through vertical interfacial coupling.” Nanoscale 7, 13808 (2015). [DOI: 10.1039/c5nr0323h]