COLLABORATIVE RESEARCH: QUANTUM SPIN CHAINS. EXTENT AND PERSISTENCE OF MAGNETIC INTERACTIONS AS A FUNCTION OF LENGTH AND SPIN

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Non-technical This research is in the field of organic materials and low-dimensional systems. It consists of the fabrication of ultra-short chains of 7 to 200 atoms in length, to test theoretical models and explore the emergence of new magnetic properties. This study provides a broader and deeper understanding of the magnetic behavior of low-dimensional systems and may have a direct impact on the development of a new generation of spintronic devices. This research has an active educational component. The project involves two graduate students who perform research for their Ph.D. thesis topic and two physics undergraduate students per semester. During these activities, students receive training at first synchrotron and neutron facilities and are exposed to state of the art advanced experimental techniques. Community outreach efforts associated with this project involve a partnership with high schools in San Antonio school districts and the production of short videos on different topics related to nanotechnology using a comical approach. These efforts are aimed to increase scientific knowledge in high school students and provide tools for science educators across the United States. Technical This research is aimed to study three fundamental problems in magnetic 1D chains: 1) the determination of the extent and persistence of short- and long-range magnetic interactions as a function of the chain's length and defects, 2) the control and modulation of the spin along the chains, and 3) the exploration of proximity effects in varying composition magnetic/non-magnetic metal chains. To achieve these objectives, the PIs have developed a method for the fabrication of macroscopic arrays of 1D chains that allow precise control of their length, composition, and spin. Specifically, this research focuses on the ultra-short (and poorly explored) chain of ~7 to 200 atoms long. Monoatomic and varying composition chains are grown by Organic Molecular Beam Epitaxy (OMBE) using metallo-phthalocyanine (MPc) superlattices (SLs). MPcs are a family of planar organic molecules with one metal atom located in the molecule's center surrounded by organic support. Many metal ions (Fe, Ni, Cu, Co, and Mn) can be substituted into the MPc giving rise to many isostructural compounds with different electronic (spin) configurations and physical properties. These molecules stack face-to-face giving rise to 1D metal chains when grown by OMBE. The orientation of the chain and its length can be controlled by substrate choice and thickness of the deposited MPc layer respectively. Moreover, using a SL structure, the chain composition, and spin can be varied by intercalating other magnetic and non-magnetic MPc layers. This project includes structural characterization (XRD and HRTEM) and magnetic measurements (SQUID, VSM, and AC susceptibility) in a broad temperature/field. Synchrotron techniques such as XMCD are used to obtain element-selective magnetic measurements and electronic configuration of the metals ions forming the varying composition chains. NEXAFS and DFT calculations allow determining the spin configuration of these elements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.