Elsa Lhotel

Highly Anisotropic Rhenium(IV) Complexes: New Examples of Mononuclear Single-Molecule Magnets

The rhenium(IV) complex (NBu4)2[ReBr4(ox)] (1) (ox = oxalate and NBu4(+) = tetra-n-butylammonium cation) has been prepared and its crystal structure determined by X-ray diffraction. The structure is made up of discrete [ReBr4(ox)](2-) anions and bulky NBu4(+) cations. Each [ReBr4(ox)](2-) anion is surrounded by six NBu4(+) cations, which preclude any significant intermolecular contact between the anionic entities, the shortest rhenium···rhenium distance being 9.373(1) Å. Variable temperature dc and ac magnetic susceptibility measurements and field-dependent magnetization experiments on polycrystalline samples of 1 reveal the occurrence of highly anisotropic magnetically isolated Re(IV) centers (S(Re) = 3/2), which exhibit slow relaxation of the magnetization at very low temperatures in a dc field. Ac measurements conducted on a polycrystalline sample of the complex (NBu4)2[ReCl4(ox)] (2) [compound isostructural to 1 whose structure and dc magnetic susceptibility study were previously reported in Tomkiewicz, A.; Bartczak, T. J.; Kruszyński, R.; Mroziński, J. J. Mol. Struct. 2001, 595, 225] show a similar behavior, both complexes thus constituting new examples of mononuclear single-molecule magnets. High-frequency and -field electron paramagnetic resonance on polycrystalline samples of 1 and 2 and on single crystals of 2 allowed for the determination for the first time of the negative sign and confirmed a significant magnitude and rhombicity (E/D) of the zero-field splitting tensor of the [ReCl4(ox)](2-) and [ReBr4(ox)](2-) centers, originating from a combination of spin-orbit coupling and low molecular symmetry. D and E values of 1 and 2 were estimated through magnetization measurements and theoretically calculated through complete active space and density functional theory methodologies.

Superconducting phase diagram of the filled skuterrudite PrOs4Sb12

We present new measurements of the specific heat of the heavy fermion superconductor PrOs4Sb12, on a sample which exhibits two sharp distinct anomalies at Tc1= 1.89K and Tc2= 1.72K. They are used to draw a precise magnetic field-temperature superconducting phase diagram ofPrOs4Sb12 down to 350~mK. We discuss the superconducting phase diagram of PrOs4Sb12 and its possible relation with an unconventional superconducting order parameter. We give a detailed analysis of Hc2(T), which shows paramagnetic limitation (a support for even parity pairing) and multiband effects.

Spin Dynamics at Very Low Temperature in Spin Ice Dy2Ti2O7

We have performed AC susceptibility and DC magnetic relaxation measurements on the spin ice system Dy 2 Ti 2 O 7 down to 0.08 K. The relaxation time of the magnetization has been estimated below 2 K down to 0.08 K. The spin dynamics of Dy 2 Ti 2 O 7 is well described by using two relaxation times [τ S (short time) and τ L (long time)]. Both τ S and τ L increase on cooling. Assuming the Arrhenius law in the temperature range 0.5–1 K, we obtained an energy barrier of 9 K. Below 0.5 K, both τ S and τ L show a clear deviation from the thermal activated dynamics toward temperature independent relaxation, suggesting a quantum dynamics.

Fluctuations and All-In-All-Out Ordering in Dipole-Octupole Nd(2)Zr(2)O(7).

By means of neutron scattering and magnetization measurements down to 90 mK, we determine the magnetic ground state of the spin-ice candidate Nd(2)Zr(2)O(7). We show that, despite ferromagnetic interactions, Nd(2)Zr(2)O(7) undergoes a transition around 285 mK towards an all-in-all-out antiferromagnetic state, with a strongly reduced ordered magnetic moment. We establish the (H,T) phase diagram in the three directions of the applied field and reveal a metamagnetic transition around 0.1 T, associated with an unexpected shape of the magnetization curves. We propose that this behavior results from the peculiar nature of the Nd^{3+} doublet, a dipolar-octupolar doublet, different from the standard Kramers doublet studied to date, thus revealing the importance of multipolar correlations in the properties of pyrochlore oxides.

From purely organic to metallo-organic chiral magnetic materials

There is presently a widespread search for materials which present magnetic ordering and appropriate chiroptical properties which would allow the observation of magneto-chiral effects. In this paper, we reflect on the possible uses of organic materials to probe this phenomenon, either as pure compounds or as their coordination compounds with metal ions.

Magnetic structure and dynamics of a strongly one-dimensional cobalt II metal-organic framework

We investigate the magnetism of the CoII4(OH)2(C10H16O4)3 metal-organic framework, which displays complex inorganic chains separated from each other by distances of 1 to 2 nm and orders at 5.4 K. The zero-field magnetic structure is determined using neutron powder diffraction: it is mainly antiferromagnetic but possesses a ferromagnetic component along the c axis. This magnetic structure persists in presence of a magnetic field. Alternating current susceptibility measurements confirm the existence of a single thermally activated regime over seven decades in frequency (E/kB≈64 K), whereas time-dependent relaxation of the magnetization after saturation in an external field leads to a two times smaller energy barrier. These experiments probe the slow dynamics of domain walls within the chains: we propose that the ac measurements are sensitive to the motion of existing domain walls within the chains, while the magnetization measurements are governed by the creation of domain walls.

Candidate quantum spin ice in the pyrochlore Pr2Hf2O7

We report the low temperature magnetic properties of the pyrochlore

Anisotropy-Tuned Magnetic Order in Pyrochlore Iridates

{\mathrm{Pr}}_{2}{\mathrm{Hf}}_{2}{\mathrm{O}}_{7}

Trihaloacetic acids: an investigation of steric and inductive ligand effects on the synthesis of [Mn12O12(O2CCX3)16(H2O)4] single-molecule magnets

. Polycrystalline and single-crystal samples are investigated using time-of-flight neutron spectroscopy and macroscopic measurements, respectively. The crystal-field splitting produces a non-Kramers doublet ground state for

Experimental signature of the attractive Coulomb force between positive and negative magnetic monopoles in spin ice

{\mathrm{Pr}}^{3+}