On‐Surface Magnetometry: The Evaluation of Superexchange Coupling Constants in Surface‐Wired Single‐Molecule Magnets

Abstract

A comfortable environment: Interaction with a gold surface fully preserves the spin structure of a Fe3Cr single-molecule magnet of current interest in molecular spintronics. Magnetic polarization at metal sites is measured over a broad temperature range (from 10 to 300 K) by X-ray magnetic circular dichroism (XMCD), which provides the required monolayer sensitivity. The data are used to evaluate Fe-Cr superexchange coupling interactions, which compare well with bulk-phase values in both sign and strength

Propeller‐Shaped Fe4 and Fe3M Molecular Nanomagnets: A Journey from Crystals to Addressable Single Molecules

“…Since chromium(III) and vanadium(III) have s i = 3/2 and 1, respectively, the ground spin state is S = 6 in 3 Cr,R [90–94] and S = 13/2 in 3 V,R . The antiparallel spin polarizations at Fe 3+ and Cr 3+ sites in the ground spin state of two 3 Cr,R complexes with R = (CH 2 ) 9 SAc and (CH 2 ) 5 SAc were directly visualized by X‐ray magnetic circular dichroism (XMCD), which is an element‐specific technique. Both 3 Cr,R and 3 V,R behave as SMMs with anisotropy barriers and blocking temperatures increasing in the order 3 Cr,R < 3 R < 3 V,R .…”

“…XMCD was used to investigate the effect of the surface on intramolecular superexchange interactions in a monolayer of 3 Cr,R [R = (CH 2 ) 5 SAc] self‐assembled on a gold substrate . In Figure a, b we report the XMCD spectra recorded at Fe‐ and Cr‐L 3 edges, respectively, as a function of temperature.…”

“…A quantitative analysis was performed by plotting the intensity of the XMCD signal as a function of temperature, as done in Figure b but now separating the contributions of the two different elements (Figure c). By fitting these data to Equation (1) with s 1 = 3/2 and s 2 = s 3 = s 4 = 5/2, a Fe–Cr superexchange coupling constant J = 14.7(7) cm –1 was obtained, identical within experimental error to that found in a bulk sample using the same experimental method [14.3(7) cm –1 ] …”

“…Each spectrum has been normalized with respect to the isotropic spectrum (average of the X‐ray absorption spectra obtained with left‐ and right‐handed circularly polarized light, not shown here). Adapted from ref …”

New Silver(I) Coordination Polymer with Fe4 Single-Molecule Magnets as Long Spacer

“…In general, clusters of this family feature easy axis anisotropy normal to the metal plane. Despite the low energy barrier of Fe 4 SMMs reaching up to 15-17 K, their chemical versatility has been exploited by creating clusters able to sublimate by fluorination of the peripheral β-diketonato ligands [15][16][17] or anchor on gold surfaces by sulfur-rich tripodal ligands [18,19], as well as modulating the spin ground state by selective replacement of the central metal ion with chromium(III) [20,21], vanadium(III) [22], or lanthanide ions [23,24]. This family of SMMs has been also characterized as single-molecule junction in scanning tunneling microscope (STM) experiments at 0.5 K [25] and through theoretical calculations for its behavior in spin-polarized transport [26], revealing how Fe 4 SMMs would be excellent candidates for molecular spintronics devices.…”