Muons and magnets

Abstract:

We report millimetre-wave and magnetic measurements on single crystals of the high-spin molecular magnet, Cr-10(OMe)(20)(O2CCMe3)(10). The susceptibility data obtained using a SQUID magnetometer indicate that this molecule has a total spin of S = 15. The temperature dependence of the magnetisation allows us to estimate the intermolecular exchange constant. The EPR spectra were obtained at different frequencies, angles and temperatures. The results are compared with numerical simulations allowing determination of the Hamiltonian parameters.

Abstract:

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.

Abstract:

The spin-crossover phenomenon is a cooperative low-spin to high-spin transition which can be initiated using temperature or light-irradiation. We have used muon-spin relaxation (μSR) to study this effect in Fe(PM-PEA) 2(NCS)2 and Fe(PMAzA)2(NCS)2. We find Gaussian or exponential muon relaxation in the high-spin phase for the two compounds, reflecting differences in their intermolecular interactions. For both compounds, the low-spin phase gives rise to root-exponential relaxation which we associate with a dilute distribution of fluctuating moments resulting from incomplete spin crossover. © 2003 Elsevier Ltd. All rights reserved.

Abstract:

We present zero-field muon spin relaxation (μ+SR) measurements on the rare earth antiferromagnet PrO2. Oscillations in the time dependence of the muon polarization, characteristic of a quasistatic magnetic field at two distinct muon sites, are observed below TN, along with relaxation dominated by the magnitude of the local field. Candidate muon sites in the material are suggested on the strength of dipole field calculations. Relaxation above TN allows a prediction of the quasielastic neutron scattering linewidth, which is discussed in terms of a simple model of magnetoelastic relaxation involving a crystal field state at an energy Δ above the ground level. The obtained value of Δ may be taken as an approximate estimate of the splitting of the Γ8 ground state of Pr4+ in the distorted fluorite structure.