Multiple Magnetization Reversal Channels Observed in a 3d-4f Single Molecule Magnet

The present study discusses the magnetic dynamics of a previously reported cyanide bridged 3d-4f dinuclear DyIIICoIII complex. Following the axial anisotropy suggested by previous Electron Paramagnetic Resonance spectroscopy (EPR) analysis, the complex turned out to show slow relaxation of the magnetization at cryogenic temperature, and this was studied in different temperature and field regimes. The existence of multichannel relaxation pathways that reverse the magnetization was clearly disclosed: a tentative analysis suggested that these channels can be triggered and controlled as a function of applied static magnetic field and temperature. Persistent evidence of a temperature independent process even at higher fields, attributable to quantum tunneling, is discussed, while the temperature dependent dynamics is apparently governed by an Orbach process. The broad distribution of relaxation rates evidenced by the ac susceptibility measurements suggest a relevant role of the intermolecular interactions in this system

Tm(III) complexes undergoing slow relaxation of magnetization: exchange coupling and aging effects

The present study focuses on the dynamical magnetic behaviour of exchange coupled 3d-4f complexes containing the scarcely considered non Kramers Tm3+ center, the 3d metal ions being either the low-spin Fe3+ (1) or the diamagnetic Co3+ (2) ion. Both complexes display field-dependent slow relaxation of magnetization. The field and temperature dependences of the relaxation rate provided indication of relevant contributions from quantum tunnelling, direct and Raman processes, with only minor effects from exchange coupling interactions. Furthermore, aged sample of 2 exhibited additional relaxation process, possibly due to solvent loss, highlighting the importance of a careful consideration of this factor when analysing the magnetization dynamics in solvated systems

Slow Relaxation of Magnetization in an Isostructural Series of Zinc–Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %

Patterned monolayers of nitronyl nitroxide radicals

We report here the results of the preliminary characterization of the monolayer obtained both by self-assembling and microcontact printing of a di-alkyl sulfide nitronyl nitroxide derivative, 11-decyl sulfanyl-undecanyl nitronyl nitroxide of which we describe the synthesis. The sulfide unit has been introduced in order to allow the grafting of the molecule to the gold surface as well as to improve the stability of the organic radical with respect to different grafting agents like thiols, whereas the two long alkyl chains have been introduced to enhance the packing order of the molecules in a self assembled monolayer structure. X-band ESR was used to demonstrate the persistence of the paramagnetic character of the radical in the self-assembled monolayers, and to study its relatively large mobility. The microcontact printed monolayer was characterized by AFM, suggesting a non-negligible mobility of the molecules on the surfaces and a strong tilting of the molecules on the surface

Chiral mononuclear lanthanide complexes derived from chiral Schiff bases: Structural and magnetic studies

A new family of mononuclear lanthanide complexes with formula [LnIII(L)Cl3] (Ln = Eu (1), Tb (2), Dy (3), Er (4), Yb (5)) and L = N,N0-bis((1,2-diphenyl-(pyridine-2-yl)methylene)-(R,R/S,S)-ethane-1,2-diamine has been obtained employing enantiomerically pure Schiff bases. The complexes have been structurally characterized using X-ray single crystal and powder diffraction. Their dynamic magnetic properties have been studied showing that this family presents slow relaxation of the magnetization under certain conditions and confirms the different behavior of each LnIII cations in isostructural complexes: only the Er one possibly relaxing via an overbarrier Orbach process, while Raman process dominates for Dy and Yb derivative

Slow magnetisation relaxation in tetraoxolene-bridged rare earth complexes

Two tetraoxolene-bridged dinuclear Dy(iii) complexes exhibit slow relaxation in ac magnetic susceptibility studies with zero-field quantum tunnelling of the magnetisation that is suppressed by the application of a dc magnetic field