Phase transitions induced by exchange coupling, magnetic field, and temperature in a strongly correlated molecular trimer with a triangular topology.

Regulating the physical properties such as the quantum phase and the Kondo effect of molecular electronic devices near critical points may play a key role in increasing the robustness of quantum memory, which is a crucial component in quantum information processing. Molecules with a triangular topology are ideal prototypes to reveal the competition among magnetic frustration, Kondo screening, and local inter-molecule exchange interactions. Herein, motivated by a recent work investigating the single-electron tunneling through a redox-active edge-fused porphyrin trimer by using a Hubbard dimer model [J. O. Thomas, J. K. Sowa, B. Limburg, X. Bian, C. Evangeli, J. L. Swett, S. Tewari, J. Baugh, G. C. Schatz, G. A. D. Briggs, H. L. Anderson and J. A. Mol, Chem. Sci., 2021, 12, 11121], we studied the phase transition, the electronic transport, and the thermodynamical properties of a real molecular trimer structure organized in a triangular topology, with and without an external magnetic field, and at zero and non-zero temperatures. Both the Hubbard electron-electron interaction and the Heisenberg exchange interaction are fully taken into account, with the aid of the state-of-the-art numerical renormalization group method. Various kinds of Kondo behaviors and quantum phase transitions are demonstrated, due to the competition among the Ruderman-Kittel-Kasuya-Yosida interaction, the direct exchange coupling, and the Zeeman effect. Our findings may offer deep insights into the manipulation of the quantum phase and the Kondo behavior in a molecular trimer with a triangular topology.

Kondo effect and RKKY interaction assisted by magnetic anisotropy in a frustrated magnetic molecular device at zero and finite temperature.

Molecular magnetic compounds, which combine the advantages of nanoscale behaviors with the properties of bulk magnetic materials, are particularly attractive in the fields of high-density information storage and quantum computing. Before molecular electronic devices can be fabricated, a crucial task is the measurement and understanding of the transport behaviors. Herein, we consider a magnetic molecular trimer sandwiched between two metal electrodes, and, with the aid of the sophisticated full density matrix numerical renormalization group (FDM-NRG) technique, we study the effect of magnetic anisotropy on the charge transport properties, illustrated by the local density of states (LDOS, which is proportional to the differential conductance), the Kondo effect, and the temperature and inter-monomer hopping robustness. Three kinds of energy peaks are clarified in the LDOS: the Coulomb, the Kondo and the Ruderman-Kittel-Kasuya-Yosida (RKKY) peaks. The local magnetic moment and entropy go through four different regimes as the temperature decreases. The Kondo temperature TK could be described by a generalized Haldane's formula, revealing in detail the process where the local moment is partially screened by the itinerant electrons. A relationship between the width of the Kondo resonant peak WK and TK is built, ensuring the extraction of TK from WK in an efficient way. As the inter-monomer hopping integral varies, the ground state of the trimer changes from a spin quadruplet to a magnetically frustrated phase, then to an orbital spin singlet through two first order quantum phase transitions. In the first two phases, the Kondo peak in the transmission coefficient reaches its unitary limit, while in the orbital spin singlet, it is totally suppressed. We demonstrate that magnetic anisotropy may also induce the Kondo effect, even without Coulomb repulsion, hence it is replaceable in the many-body behaviours at low temperature.

Antiferroelectrics and Magnetoresistance in La0.5Sr0.5Fe12O19 Multiferroic System.

The appearance of antiferroelectrics (AFE) in the ferrimagnetism (FM) system would give birth to a new type of multiferroic candidate, which is significant to the development of novel devices for energy storage. Here we demonstrate the realization of full antiferroelectrics in a magnetic La0.5Sr0.5Fe12O19 system (AFE+FM), which also presents a strong magnetodielectric response (MD) and magnetoresistance (MR) effect. The antiferroelectric phase was achieved at room temperature by replacing 0.5 Sr2+ ions with 0.5 La2+ ions in the SrFe12O19 compound, whose phase transition temperature of ferroelectrics (FE) to antiferroelectrics was brought down from 174 °C to -141 °C, while the temperature of antiferroelectrics converting to paraelectrics (PE) shifts from 490 °C to 234 °C after the substitution. The fully separated double P-E hysteresis loops reveal the antiferroelectrics in La0.5Sr0.5Fe12O19 ceramics. The magnitude of exerting magnetic field enables us to control the generation of spin current, which induces MD and MR effects. A 1.1T magnetic field induces a large spin current of 15.6 n A in La0.5Sr0.5Fe12O19 ceramics, lifts up dielectric constants by 540%, and lowers the resistance by -89%. The magnetic performance remains as usual. The multiple functions in one single phase allow us to develop novel intelligent devices.

Multiferroic La0.2Pb0.7Fe12O19 ceramics: Ferroelectricity, ferromagnetism and colossal magneto-capacitance effect.

The mutual control of the electric and magnetic properties of a multiferroic solid is of fundamental and great technological importance. In this article, the synthesis procedure of La0.2Pb0.7Fe12O19 ceramics was briefly described and the data acquired for the materials characterization is presented. This data article is related to the research article-Acta Mater. 2016, 121, 144 (j.actamat.2016.08.083). Electric polarization hysteresis loop and I-V curve, which help to confirm the ferroelectricity of La0.2Pb0.7Fe12O19 ceramics, were presented. Strong magnetic polarization data was also presented. The great variation of the dielectric constants along with the magnetic field has been presented which helped to demonstrat the giant magnetocapacitance of La0.2Pb0.7Fe12O19. All the datasets were collected at room temperature. Large ferroelectricity, strong magnetism and colossal magneto-capacitance effect have been all realized in one single phase La0.2Pb0.7Fe12O19 at room temperature.

Dual-emitting nanocomposites derived from rare-earth compound nanotubes for ratiometric fluorescence sensing applications.

A new class of ratiometric fluorescence sensors composed of rare-earth (RE) compound nanotubes is described. Polyethylenimine-coated yttrium hydroxide fluoride nanotubes (YHF NTs) that were synthesized hydrothermally exhibit highly efficient fluorescence when doped with RE ions. The polyethylenimine on the NTs facilitates the incorporation of phosphors such as quantum dots or organic dyes onto the NT surface to produce dual-emitting nanocomposites which are excellent ratiometric fluorescence sensors. The phosphor layer and underlying tubes in the nanocomposites act as the indicator and reference probes, respectively. This ratiometric fluorescence method which can be applied to the detection of heavy metals in solutions, temperature sensing, and pH sensing boasts high sensitivity and selectivity as well as better accuracy than traditional intensity-based fluorescence methods.