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Creators/Authors contains: "McCandless, Gregory T."

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  1. Free, publicly-accessible full text available March 1, 2025
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  3. For some intermetallic compounds containing lanthanides, structural transitions can result in intermediate electronic states between trivalency and tetravalency; however, this is rarely observed for praseodymium compounds. The dominant trivalency of praseodymium limits potential discoveries of emergent quantum states in itinerant 4f1systems accessible using Pr4+-based compounds. Here, we use in situ powder x-ray diffraction and in situ electron energy-loss spectroscopy (EELS) to identify an intermetallic example of a dominantly Pr4+state in the polymorphic system Pr2Co3Ge5. The structure-valence transition from a nearly full Pr4+electronic state to a typical Pr3+state shows the potential of Pr-based intermetallic compounds to host valence-unstable states and provides an opportunity to discover previously unknown quantum phenomena. In addition, this work emphasizes the need for complementary techniques like EELS when evaluating the magnetic and electronic properties of Pr intermetallic systems to reveal details easily overlooked when relying on bulk magnetic measurements alone.

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    Free, publicly-accessible full text available January 26, 2025
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  5. In solid materials, non-trivial topological states, electron correlations and magnetism are central ingredients for realizing quantum properties, including unconventional superconductivity, charge and spin density waves and quantum spin liquids. The kagome lattice, made up of cornersharing triangles, can host these three ingredients simultaneously and has proved to be a fertile platform for studying diverse quantum phenomena including those stemming from the interplay of these ingredients. This Review introduces the fundamental properties of the kagome lattice and discusses the complex phenomena observed in several materials systems, including the intertwining of charge order and superconductivity in some kagome metals, the modulation of magnetism and topology in some kagome magnets, and the combination of symmetry breaking and Mott physics in ‘breathing’ kagome insulators. The Review also highlights open questions in the field and future research directions in kagome systems. 
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    Free, publicly-accessible full text available September 27, 2024
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  7. Abstract

    The crystal structure, electron energy-loss spectroscopy (EELS), heat capacity, and anisotropic magnetic and resistivity measurements are reported for Sn flux grown single crystals of orthorhombic Pr2Co3Ge5(U2Co3Si5-type,Ibam). Our findings show thato-Pr2Co3Ge5hosts nearly trivalent Pr ions, as evidenced by EELS and fits to temperature dependent magnetic susceptibility measurements. Complex magnetic ordering with a partially spin-polarized state emerges nearTsp= 32 K, with a spin reconfiguration transition nearTM= 15 K. Heat capacity measurements show that the phase transitions appear as broad peaks in the vicinity ofTspandTM. The magnetic entropy further reveals that crystal electric field splitting lifts the Hund’s rule degeneracy at low temperatures. Taken together, these measurements show that Pr2Co3Ge5is an environment for complexfstate magnetism with potential strongly correlated electron states.

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