Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userField-induced quantum magnetism in the verdazyl-based charge-transfer salt $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$
110
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We successfully synthesized a verdazyl-based charge-transfer salt $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$, which has an $S_{rm{V}}$=1/2 on the radical $o$-MePy-V-($p$-Br)$_2$ and an $S_{rm{Fe}}$=5/2 on the FeCl$_4$ anion. $Ab$ $initio$ molecular orbital calculations indicate the formation of an $S_{rm{V}}$=1/2 honeycomb lattice composed of three types of exchange interaction with two types of inequivalent site. Further, the $S_{rm{V}}$=1/2 at one site is sandwiched by $S_{rm{Fe}}$=5/2 spins through antiferromagnetic (AF) interactions. The magnetic properties indicate that the dominant AF interactions between the $S_{rm{V}}$ = 1/2 spins form a gapped singlet state, and the remaining $S_{rm{Fe}}$ = 5/2 spins cause an AF order. The magnetization curve exhibits a linear increase up to approximately 7 T, and an unconventional 5/6 magnetization plateau appears between 7 T and 40 T. We discuss the differences between the effective interactions associated with the magnetic properties of the present compound and ($o$-MePy-V)FeCl$_4$. We explain the low-field linear magnetization curve through a mean-field approximation of an $S_{rm{Fe}}$ = 5/2 spin model. At higher field regions, the 5/6 magnetization plateau and subsequent nonlinear increase are reproduced by the $S_{rm{V}}$ = 1/2 AF dimer, in which a particular internal field is applied to one of the spin sites. The ESR resonance signals in the low-temperature and low-field regime are explained by conventional two-sublattice AF resonance modes with easy-axis anisotropy. These results demonstrate that exchange interactions between $S_{rm{V}}$ = 1/2 and $S_{rm{Fe}}$ = 5/2 spins in $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$ realize unconventional magnetic properties with low-field classical behavior and field-induced quantum behavior.
rate research
Read More
The low and high-temperature phases of V$_4$O$_7$ have been studied by textit{ab initio} calculations. At high temperature, all V atoms are electronically equivalent and the material is metallic. Charge and orbital ordering, associated with the distortions in the V pseudo-rutile chains, occur below the metal-insulator transition. Orbital ordering in the low-temperature phase, different in V$^{3+}$ and V$^{4+}$ chains, allows to explain the distortion pattern in the insulating phase of V$_4$O$_7$. The in-chain magnetic couplings in the low-temperature phase turn out to be antiferromagnetic, but very different in the various V$^{4+}$ and V$^{3+}$ bonds. The V$^{4+}$ dimers formed below the transition temperature form spin singlets, but V$^{3+}$ ions, despite dimerization, apparently participate in magnetic ordering.
We have performed $^{77}$Se NMR on a single crystal sample of the field induced superconductor $lambda$-(BETS)$_{2}$FeCl$_{4}$. Our results obtained in the paramagnetic state provide a microscopic insight on the exchange interaction $J$ between the spins textbf{s} of the BETS $pi$ conduction electrons and the Fe localized $d$ spins textbf{S}. The absolute value of the Knight shift textbf{K} decreases when the polarization of the Fe spins increases. This reflects the ``negative spin polarization of the $pi$ electrons through the exchange interaction $J$. The value of $J$ has been estimated from the temperature and the magnetic field dependence of textbf{K} and found in good agreement with that deduced from transport measurements (L. Balicas textit{et al}. Phys. Rev. Lett. textbf{87}, 067002 (2001)). This provides a direct microscopic evidence that the field induced superconductivity is due to the compensation effect predicted by Jaccarino and Peter (Phys. Rev. Lett. textbf{9}, 290 (1962)). Furthermore, an anomalous broadening of the NMR line has been observed at low temperature, which suggests the existence of charge disproportionation in the metallic state neighboring the superconducting phase.
The recently proposed multiferroic state of the charge-transfer salt {kappa}-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl [P. Lunkenheimer et al., Nature Mater., vol. 11, pp. 755-758, Sept. 2012] has been studied by dc-conductivity, magnetic susceptibility and measurements of the dielectric constant on various, differently prepared single crystals. In the majority of crystals we confirm the existence of an order-disorder-type ferroelectric state which coincides with antiferromagnetic order. This phenomenology rules out scenarios which consider an inhomogeneous, short-range-ordered ferroelectric state. Measurements of the dielectric constant and the magnetic susceptibility on the same crystals reveal that both transitions lie very close to each other or even collapse, indicating that both types of order are intimately coupled to each other. We address issues of the frequency dependence of the dielectric constant {epsilon} and the dielectric loss {epsilon} and discuss sample-to-sample variations.
In the spinel compound GeCo$_2$O$_4$, the Co$^{2+}$ pyrochlore sublattice presents remarkable magnetic field-induced behaviors that we unveil through neutron and X-ray single-crystal diffraction. The Neel ordered magnetic phase is entered through a structural lowering of the cubic symmetry. In this phase, when a magnetic field is applied along a 2-fold cubic direction, a spin-flop transition of one fourth of the magnetic moments releases the magnetic frustration and triggers magnetostructural effects. At high field, these ultimately lead to an unusual spin reorientation associated to structural changes.
Using neutron diffraction, we have studied the magnetic field effect on charge structures in the charge-ordered multiferroic material LuFe$_2$O$_4$. An external magnetic field is able to change the magnitude and correlation lengths of the charge valence order even before the magnetic order sets in. This affects the dielectric and ferroelectric properties of the material and induces a giant magneto-electric effect. Our results suggest that the magneto-electric coupling in LuFe$_2$O$_4$ is likely due to magnetic field effect on local spins, in clear contrast to the case in most other known multiferroic systems where the bulk magnetic order is important.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
