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Single-chain magnets are molecular spin chains displaying slow relaxation of the magnetisation on a macroscopic time scale. To this similarity with single-molecule magnets they own their name. In this chapter the distinctive features of single-chain magnets as opposed to their precursors will be pinpointed. In particular, we will show how their behaviour is dictated by the physics of thermally-excited domain walls. The basic concepts needed to understand and model single-chain magnets will also be reviewed., Comment: 31 pages, 6 figures. Book chapter in "Molecular Magnets; Physics and Applications" edited by J. Bartolom\'e, F. Luis, J. Fernandez to be published by Springer-Verlag (2013)

The measurement of spin noise in nuclei was pioneered on bulk samples more than two decades ago. An ensemble of spins can produce a coherent signal at the frequency of a static magnetic field, known as spin noise, an effect due to the statistical polarization of small ensembles. The difficulty of these measurements is that the signal is extremely small, even if electron spins are detected. Although the statistical polarization of N spins dominates the Boltzmann statistics if N approaches unity, a more sensitive tool is requested to measure the polarization of the magnetic moment of a single spin. In this paper we report on the verification of recent results on the detection of spin noise from paramagnetic molecules of BDPA alpha,gamma,Bisdiphenylene,betha,phenylallyl by Durkan and coworkers. C. Durkan and M. E. Welland, Appl. Phys. Lett. 80, 458 2002 We also present new results on a second paramagnetic specie, DPPH (1,1,Diphenyl,2.picrylhydrazyl), deposited on Au(111) surfaces. ESR spectra from ultrathin films of DPPH and BDPA grown on Au(111) are reported. We prove that the paramagnetic molecules preserve their magnetism on the surface. These data and a thorough analysis of the signal recovery apparatus help to understand the low statistical recurrence of the spin noise in the data set . A thorough description of the experimental apparatus together with an analysis of the parameters that determine the sensitivity are also presented., Comment: Figure resolution limited by file size. Contact author for 300*300 dpi pictures

The magnetic properties of the first odd-member antiferromagnetic ring comprising eight chromium(III) ions, S=3/2 spins, and one nickel(II) ion, S=1 spin, are investigated. The ring possesses an even number of unpaired electrons and a S=0 ground state but, due to competing AF interactions, the first excited spin states are close in energy. The spin frustrated ring is visualized by a Moebius strip. The ?knot? of the strip represents the region of the ring where the AF interactions are more frustrated. In the particular case of this bimetallic ring electron paramagnetic resonance (EPR) has unambiguously shown that the frustration is delocalized on the chromium chain, while the antiparallel alignment is more rigid at the nickel site., Comment: 6 pages, 8 figures

Reading and manipulating the spin status of single magnetic molecules is of paramount importance both for applicative and fundamental purposes. The possibility to combine Electron Spin Resonance (ESR) and Scanning Tunnelling Microscopy (STM) has been explored one decade ago. A few experiments have raised the question whether or not an EPR spectrum of single molecule is detachable. Only a few data have been reported in modern surface science literature. To date it has yet to be proven to which extent ESR can be reliably and reproducibly performed on single molecules. We are setting up a new ESR-STM (spectrometer) to verify and study the effect of spin-spin correlations in the frequency spectrum of the tunneling current which flows through a single magnetic adsorbate and a metal surface. Here we discuss, the major experimental challenges that we are attempting to overcome., Comment: Modified 18/09/04. Accepted : Proceedings IEEE NANO 2004

A high-frequency (95 GHz) EPR study is reported on single crystals of the planar tetranuclear complex Fe4(OCH3)6(dpm)6 (where Hdpm = dipivaloylmethane), which has been previously shown to present typical single-molecule magnet behaviour. The spectra, all originating from the S = 5 ground state, possess quasi-axial symmetry along the normal to the plane defined by the four Fe(III) ions. The measured spectra are shown to belong to three different structural variations of the compound, resulting from disorder in the ligands around two of the Fe(III) ions. Accurate values could be obtained for the second- and fourth-order crystal field parameters related to the parallel EPR-spectra, while the other parameters could be determined only for the dominant species. The separation between individual lines is decreasing and vanishing with increasing temperature. This effect is attributed to the contribution of fast relaxing excited states, whose population is varying with temperature., Comment: 13 pages, 10 figures. To be published in The Journal of Physical Chemistry

The first X-ray magnetic circular dichroism (XMCD) spectra on the title compounds are presented. In Mn12 the Mn(III) and Mn(IV) contributions are clearly apparent and evidence the opposite spin arrangement of the two ions. For Fe8 the typical two peak structure of Fe(III) compounds is found. Quantitative analysis yielded for both compounds a negligible . This is the first direct experimental evidence of the quenching of the angular momentum in these systems. For Fe8 we found =1.14 in mB units per Fe atom, in reasonable agreement with the S=10 ground state assumed for in this system., Comment: 7 pages 7 figures

A detailed multifrequency high field - high frequency EPR (95-285 GHz) study has been performed on the single-molecule magnet of formula [Fe8O2(OH)12(tacn)6]Br8 9H2O, where tacn=1,4,7-triazacyclononane. Polycrystalline powder spectra have allowed estimating the zero field splitting parameters up to the fourth order terms. The single crystal spectra have provided the principal directions of the magnetic anisotropy of the cluster. These results have been compared to an evaluation of the intra-cluster dipolar contribution to the magnetic anisotropy, suggesting that single ion anisotropy is mainly contributing to the magnetic anisotropy. The role of the transverse magnetic anisotropy in determining the height of the barrier for the reversal of the magnetization is also discussed., Comment: 13 pages, 8 figures