A high-energy inelastic neutron scattering investigation of the Gd-Co exchange interactions in GdCo4B: Comparison with density-functional calculations

International audienceInelastic neutron scattering is used to quantify the Gd-Co exchange interaction in GdCo4B. A significant reduction is observed in comparison with the GdCo5 compound. A mean value of 130 T is obtained for the exchange field on the two Gd sites in GdCo4B. The experimental results are compared with density-functional calculations. The local atomic magnetic moments calculated using the LSDA+U approximation are reported for each atomic site of the GdCo4B crystal structure. These calculations demonstrate that the two nonequivalent Gd crystal sites experience a significantly different exchange interaction, a difference that is discussed in the light of the local atomic environment. The observed reduction of the exchange field occurring upon substituting B for Co in GdCo5 is mainly caused by the decrease of the Co magnetic moment, whereas the Gd-Co coupling constant is found to be almost the same in both GdCo5 and GdCo4B

Magnetic Properties of (Fe,Co)₂B Alloys With Easy-Axis Anisotropy

Intrinsic magnetic properties of (Fe 1-xCo x) 2B (x = 0.20, 0.25, 0.30, 0.35) alloys have been studied on single crystals. Temperature dependence of both magnetocrystalline anisotropy constant K 1 and spontaneous magnetization M s has been determined from magnetization isotherms measured between 10 and 1000 K. The highest anisotropy constant K 1 was obtained at x = 0.25, K 1 = 494 kJ/m 3 at T = 10 K. The Curie temperature decreased from 966 to 930 K as x increased from 0.2 to 0.35

Electron spins interaction in the spin-Peierls phase of the organic spin chain (o-DMTTF)2X (X = Cl, Br, I)

International audienceWe investigate the electron spin resonance of the organic spin-Peierls chain (o-DMTTF)2X with X = Cl, Br and I. We describe the temperature dependence of the spin gap during the phase transition and quantify the dimerization parameter δ. At the lowest temperatures, the susceptibility is governed by defects in the spin dimerized chain. Such strongly correlated defects are the consequence of breaks in the translational symmetry of the chain. In the vicinity of the defects the spins are polarized antiferomagnetically forming a magnetic soliton: a spin 1 2 quasi-particle of size ruled by δ pinned to the defects. For (o-DMTTF)2Br and (o-DMTTF)2Cl, we show that the one-half of the total number of solitons are in isolation (as singles) whereas the other half form pairs (soliton dimers)with a strong magnetic coupling. The Rabi oscillations of both the single-soliton and the soliton-dimer are observed, which is a prerequisite in the context of quantum information

Design and synthesis of a new binucleating ligand via cobalt-promoted C-N bond fusion reaction. Ligand isolation and its coordination to nickel, palladium, and platinum

A new polydentate bridging ligand, NH4C5N=NC6H4N(H)C5H4N (HL2), is synthesized by the cobalt-mediated phenyl ring amination of coordinated NH4C5N=NC6H5. The green cobalt complex intermediate [Co(L2)2](ClO4), [1](ClO4), and the free ligand HL2 were isolated and characterized. The X-ray structure of [H2L2](ClO4) is reported. The ligand, upon deprotonation, behaves as a bridging ligand. It reacts with NiCl2·6H2O and Na2[PdCl4] to produce dimetallic complexes, [Ni2Cl2(L2)2], 2, and [Pd2(L2)2](ClO4)2, [3](ClO4)2, respectively. X-ray structures of these two dimetallic complexes are reported. The structure of the dinickel complex, in particular, is unique. In this complex, the two deprotonated secondary amine nitrogens of the two [L2]- ligands bind to two nickel centers simultaneously forming a planar Ni2N2 arrangement. The complex [3](ClO4)2 is diamagnetic while the complex 2 is paramagnetic. The results of magnetic measurements on the dinickel complex in the temperature range 1.8-300 K are reported. The system can be described as a single spin S=2 in the low-temperature range T<< J/k whereas at high temperatures, T>> J/k, it behaves as two independent spins S=1.The reaction of [L2]- with K2[PtCl4], however, yielded a monometallic platinum complex, [PtCl3(L2)], 5, where the pyridyl nitrogen of the aminopyridyl function remained unused. The X-ray structure of the complex 4a is reported. The bond lengths along the ligand backbones in all the complexes indicate extensive π -delocalization. Spectral data of the complexes are reported and compared

Influence of thermal treatment on magnetocaloric properties of Gd cold rolled ribbons

This work reports the influence of heat treatment on the magnetocaloric effect of cold-rolled Gd ribbons. A significant depression of magnetic and thermodynamical properties occurs in severely deformed ribbons. However, it is possible to recover the initial values, characteristic of polycrystals by way of heat treatment. The heat treatment regimes are directly connected with the degree of plastic deformation. The proposed approach is convenient for manufacturing magnetocaloric materials in the form of thin ribbons for magnetic refrigerators

High magnetic field study of the Tm2Fe17 and Tm2Fe17D3.2 compounds

International audienceA magnetization study of a Tm2Fe17 single crystal and aligned powder of the deuteride Tm2Fe17D3.2 has been carried out in steady (14 T) and pulsed (60 T and, in one case, up to 74 T) magnetic fields at temperatures between 1.5 and 300 K. Tm2Fe17 is a ferrimagnet with T-C = 295 K and a spontaneous moment of 22 mu(B)/f.u. at T = 4.2 K. Of particular interest are low-temperature magnetization curves along the sixfold crystal axis c, which is an easy direction in Tm2Fe17 and a hard direction in the deuteride. In either case the magnetization increases with magnetic field undulatorily in broad steps whose height is a multiple of the atomic moment of Tm, mu(Tm) = 7 mu(B). In Tm2Fe17, the positions of the steps yield information on the Fe-Tm molecular field, 48 T on the Tm 2d site and 60 T on the Tm 2b site, whereas the crystal field parameter A(66) is found from the widths of the steps: A(66)(b) = -35 Ka(0)(-6) and A(66)(d) = -26 Ka(0)(-6) (here a(0) is the Bohr radius). It also proves possible to estimate the other sixth-order crystal field parameter: A(60) similar to -4 Ka(0)(-6) (on average for both sites). Less information can be extracted from the powder data for the deuteride. Thus, the mean molecular field on Tm in Tm2Fe17D3.2 is found to be 49 T or 9% less than in the parent binary compound