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Zapf, Vivien

Publications and source records attributed to Zapf, Vivien.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Conductive surface states and Kondo exhaustion in insulating YbIr 3 Si 7

The interplay of Kondo screening and magnetic ordering in strongly correlated materials containing local moments is a subtle problem. Usually the number of conduction electrons per unit cell matches or exceeds the number of moments, and a Kondo-screened heavy Fermi liquid develops at low temperatures. Changing the pressure, magnetic field, or chemical doping can displace this heavy Fermi liquid in favor of a magnetically ordered state. Alternatively, Kondo singlet formation can be suppressed when the number of conduction electrons is small compared to the number of magnetic moments, known as the Kondo exhaustion scenario. Furthermore we report the discovery of such an “exhausted” Kondo lattice material, YbIr 3 Si 7 , where the bulk electrical conductivity tends to zero in the antiferromagnetic state below the Néel temperature T N = 4.1 K, as all the free carriers are consumed in the formation of Kondo singlets. By contrast, the surface is conducting, as the Yb 3+ ions relax into larger nonmagnetic Yb 2+ in the presence of reduced chemical pressure, which shifts the chemical potential.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Evidence of dynamical effects and critical field in a cobalt spin crossover complex

The [Co(SQ) 2 (4-CN-py) 2 ] complex exhibits dynamical effects over a wide range of temperature. Additionally, the orbital moment, determined by X-ray magnetic circular dichroism (XMCD) with decreasing applied magnetic field, indicates a nonzero critical field for net alignment of magnetic moments, an effect not seen with the spin moment of [Co(SQ) 2 (4-CN-py) 2 ].

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Accessing One-Dimensional Chains of Halogenoindates(III) in Organic–Inorganic Hybrids

Organic-inorganic hybrids of halogenoindates(III) are typically represented by one of the zero-dimensional units: InX 4 – , InX 5 2– , InX 6 3– , or In 2 X 11 5– . Higher dimensional anionic forms, although not forbidden, have remained almost elusive. Here, in this study, we report for the first time In 3+ -based organic–inorganic hybrids, (C 4 H 5 N 2 S) 2 InCl 5 and (C 4 H 5 N 2 S) 2 InBr 5 , with 1D anionic chains of trans-halide-bridged InX 6 octahedra whose formation is guided by 2-mercaptopyrimidinium cations (C 4 H 5 N 2 S + ). The chains are characterized by the significant ease of deformation, which is reflected in the elongation of the bridging bonds or the displacement of In 3+ ions. The materials show a robust band gap predominantly governed by C 4 H 5 N 2 S + cations. Dielectric relaxation processes in (C 4 H 5 N 2 S) 2 InBr 5 arise from the cations’ dynamics and suggest the ability of the brominated system to accommodate even larger cations. Our work represents a successful attempt to expand the structural diversity of halogenoindates(III) and opens a pathway to reach multifunctional 1D In 3+ -based hybrids.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Giant magnetostriction and nonsaturating electric polarization up to 60 T in the polar magnet $\mathrm{CaBaCo_4O_7}$

Giant magnetostriction in insulating magnetic materials is highly required for applications but is rarely observed. Here we show that giant magnetostriction (> 1500 ppm) can be achieved in an insulating transition metal oxide CaBaCo 4 O 7 where the ferrimagnetic ordering at T c ~ 62K is associated with a huge change in the lattice. Moreover, because this material is pyroelectric with a nonswitchable electric polarization (P), the giant magnetostriction results in a pronounced magnetoelectric effect—a huge change of electric polarization (ΔP ~ 1.6μC/cm 2 ) in response to the applied magnetic field up to 60 T. Geometric frustration as well as the orbital instability of Co 2+ /Co 3+ ions is believed to play a crucial role in the giant magnetostriction. Here our study provides insights on how to achieve both giant magnetostriction and pronounced magnetoelectric effect in insulating transition metal oxides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗