Materials Science Research Lecture
***Refreshments at 3:45pm in Noyes lobby
Abstract:
Intercalated transition metal dichalcogenides (TMDs) provide a versatile platform for exploring the interplay between structural symmetry and complex magnetism. I will present our work on how the synthesis and crystal growth conditions lead to complex magnetic phase diagrams of intercalated NbSe2 and TaSe2, which are TMDs with metallic properties. We demonstrate intercalation of both cobalt and manganese and highlight how stoichiometry and thermal history drive macroscopic properties.
In CoxNbSe2, two primary phases emerge: a centrosymmetric P63/mmc structure at x = ¼ hosting A-type antiferromagnetic (AFM) order (TN 169 K), and a non-centrosymmetric P6322 structure at x = 1/3 characterized by a spin density wave phase (TN 28 K). The former has also been proposed as a viable candidate for altermagnetism. At intermediate concentrations, these distinct nuclear substructures can coexist within a single-crystal superlattice, while synthesis cooling rates further tune the local sublattice domains to produce spin-glass-like behavior. Similar results are found for the Ta analogue of the NbSe2 system. For the case of Mn-intercalation we observe via neutron scattering studies, long-range spin density wave behavior giving way to metamagnetic transitions and eventually ferromagnetism at high external magnetic fields. Collectively, these results demonstrate that the symmetry, concentration, and local ordering of intercalated cations are the fundamental drivers of complex itinerant magnetic order in the group-V TMDs.
More about the Speaker:
Efrain E. Rodriguez has established a program in solid-state and materials chemistry with a multidisciplinary approach for the preparation and study of functional inorganic materials. Through combined X-ray and neutron scattering studies, he elucidates structure-function relationships in magnetic and quantum materials. Efrain received his B.S. from the Massachusetts Institute of Technology and his PhD from the University of California, Santa Barbara. After his PhD, Efrain went to the National Institute of Standards and Technology (NIST) for his National Research Council post-doctoral fellowship.
Efrain received the Margaret C. Etter Early Career Award in 2019 from American Crystallographic Association and the CAREER award from the NSF. In 2019, he joined the Board of Directors at the American Institute of Physics. In 2022, he was elected to the US National Committee on Crystallography and the Executive Committee of the Neutron Scattering Society of America. He was awarded the Alexander von Humboldt Fellowship for Experienced Researchers in 2022 to work as a visiting researcher at the Max Planck Institute in Solid State Research in Stuttgart, Germany. In 2023, he was recognized by the University of Maryland as a Distinguished Scholar Teacher, and in 2024 he was elected to the Board of Directors for SACNAS.