Two hybrid organometallic-inorganic layered magnets from the series [Z(III)CP*(2)] [(MMIII)-M-II (ox)(3)] studied with mu(+) SR

We present zero-field muon spin relaxation (ZF-mu(+)SR) measurements on two examples of a new series of hybrid organometallic-inorganic layered magnets, namely ferromagnetic [FeCp2*][MnCr(ox)(3)] and ferrimagnetic [CoCp2*][FeFe(ox)(3)] (where ox = oxalate and Cp-* = pentame- thyl-cyclopentadienyl). Both materials show multi-component muon spin precession signals characteristic of quasistatic magnetic fields at several distinct muon sites. The temperature dependence of the precession frequencies allow critical exponents to be extracted. Possible muon sites are discussed on the basis of dipole field calculations

Magnetic order and local field distribution in the hybrid magnets [FeCp*(2)][MnCr(ox)(3)] and [CoCp*(2)][FeFe(ox)(3)]: a muon spin relaxation study

Zero-field muon spin relaxation (μ+SR) measurements on materials from the series [ZIIICp*2][M IIMIII(ox)3] show precession signals at several frequencies, characteristic of quasistatic magnetic fields at up to three distinct muon sites

Brief encounter at the molecular level: what muons tell us about molecule-based magnets

Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin-1/2, a lifetime of 2.2 mu s, about one-ninth of the proton mass and a magnetic moment of approximately 1/200 mu(B). Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a sample. This experimental technique has found particular application to the problem of hydrogen in semiconductors, as well as the study of the vortex lattice in both high-temperature and organic superconductors. Nevertheless, it has been most widely employed in the field of magnetism. We describe how our experiments using spin-polarized muons have been used to provide information about organic ferromagnets, molecular magnets, spin-chains and single molecule magnets

A Chiral Bipyrimidine-Bridged Dy-2 SMM: A Comparative Experimental and Theoretical Study of the Correlation Between the Distortion o f the DyO6N2 Coordination Sphere and the Anisotropy Barrier

Chiral bipyrimidine-bridged dinuclear Ln(III) complexes of general formula [(mu-bipym){((+)-tfacam)(3)Ln}(2)] and [(mu-bipym){((-)-tfacam)(3)Ln}(2)], have been prepared from the assembly of Ln(AcO)(3)center dot nH(2)O (Ln(III) = Dy, Gd), (+)/(-)-3-(trifluoroacetyl)camphor enantiopure ligands ((+)/(-)-Htfacam) and bipyrimidine (bipym). The structure and chirality of these complexes have been supported by single-crystal X-Ray diffraction and circular dichroism. The study of the magnetic properties of the Gd-III complexes revealed a very weak antiferromagnetic interaction between the Gd-III ions through the bipyrimidine bridging ligand. Ab initio CASSCF calculations indicated that the ground Kramers doublet (KD) of both Dy-III centers is almost purely axial with the anisotropy axis located close to the two tfacam ligands at opposite sides of each Dy-III atom, which create an axial crystal field. In keeping with this, ac dynamic measurements indicated slow relaxation of the magnetization at zero field with U-eff = 55.1 K, a pre-exponential factor of tau(o) = 2.17.10(-6) s and tau(QTM) = 8 mu s. When an optimal dc field of 0.1 T is applied, QTM is quenched and U-eff increases to 75.9 K with tau(o) = 6.16 x 10(-7) s. The DyN2O8 coordination spheres and SMM properties of [(mu-bipym){((+)-tfacam)(3)Ln}(2)] and their achiral [(Dy(beta-diketonate)(3))(2)(mu-bpym)]analogous have been compared and a magneto-structural correlation has been established, which has been supported by theoretical calculations. In contrast to the Gd-III compounds, the magnetic exchange interaction between the Dy-III ions has been calculated to be very weak and, generally, ferromagnetic in nature. Relaxation mechanisms for [(mu-bipym){((+)-tfacam)(3)Ln}(2)] and previously reported analogous have been proposed from ab initio calculations. As the magnetic exchange interaction found to be very weak, the observed magnetization blockade in these systems are primarily dictated by the single ion anisotropy of Dy-III ions

Brief encounter at the molecular level: what muons tell us about molecule-based magnets

Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin-1/2, a lifetime of 2.2 mu s, about one-ninth of the proton mass and a magnetic moment of approximately 1/200 mu(B). Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a sample. This experimental technique has found particular application to the problem of hydrogen in semiconductors, as well as the study of the vortex lattice in both high-temperature and organic superconductors. Nevertheless, it has been most widely employed in the field of magnetism. We describe how our experiments using spin-polarized muons have been used to provide information about organic ferromagnets, molecular magnets, spin-chains and single molecule magnets

Magnetoresistance studies of the ferromagnetic molecular metal (BEDT-TTF)(3)[MnCr(C2O4)(3)] under pressure

(BEDT-TTF)3[MnCr(C2O4)3] is the first ferromagnetic molecular metal, in which organic layers of BEDT-TTF alternate with infinite layers of the bimetallic oxalate complex [MnCr(C2O4)3]-. While the bimetallic layer undergoes a magnetic phase transition into a canted ferromagnetic state at 5.5 K, the metallic character of the conductivity is not affected by the magnetic transition [Nature 408 (2000) 447]. We performed magnetoresistance measurements (B≤17 T) at low temperatures (T≥900 mK) and under hydrostatic pressures of up to 2.0 GPa. Oscillations in the magnetoresistance develop under pressure that can be interpreted as Shubnikov-de Haas oscillations, if an internal magnetic field is taken into account. These measurements can thus be interpreted as a measure of the internal magnetic field in the conduction layer caused by the adjacent magnetic oxalate layers. © 2002 Elsevier Science B.V. All rights reserved