A Three-Pronged Attack To Investigate the Electronic Structure of a Family of Ferromagnetic Fe₄Ln₂ Cyclic Coordination Clusters: A Combined Magnetic Susceptibility, High-Field/High-Frequency Electron Paramagnetic Resonance, and ⁵⁷Fe Mössbauer Study

Abstract

We present the synthesis, structure, magnetic properties, as well as the Mössbauer and electron paramagnetic resonance studies of a ring-shaped [FeLn(Htea)(μ-N)(N)(piv)] (Ln = Y 1, Gd 2, Tb 3, Dy 4, Ho 5, Er, 6) coordination cluster. The Dy, Tb, and Ho analogues show blocking of the magnetization at low temperatures without applied fields. The anisotropy of the 3d ion and the exchange interaction between 3d and 4f ions in FeLn complexes are unambiguously determined by high-field/high-frequency electron paramagnetic resonance measurements at low temperature. Ferromagnetic exchange interaction J is found which decreases upon variation of the Ln ions to larger atomic numbers. This dependence is similar to the behavior shown in the effective barrier values of complexes 3-5. Further information about the anisotropy of the Ln ions was gathered with Fe Mössbauer spectroscopy, and the combination of these methods provides detailed information regarding the electronic structure of these complexes.

161Dy Time‐Domain Synchrotron Mössbauer Spectroscopy for Investigating Single‐Molecule Magnets Incorporating Dy Ions

“…[5] Because of their large magnetic moments and their strong magnetic anisotropy,l anthanide ions in suitable ligand fields are ideal candidates for SMMs. [12,15,16] Herein, we report on establishing 161 Dy time-domain synchrotron Mçssbauer spectroscopy (SMS) as anovel spectroscopic tool to study magnetic properties in Dy-containing molecules and in particular in SMMs.T his technique,a lso called nuclear forward scattering (NFS), makes use of the 161 Dy nucleus as aprobe sensing the Dy magnetization via the hyperfine interactions,w hich are effective between the Dy electron shell and the 161 Dy nucleus. [9,10] Magnetic properties of molecular spin systems like SMMs are typically studied by alternating (ac) and direct current magnetic measurement methods,electron spin resonance,and nuclear magnetic resonance.…”

“…[12][13][14] Thei ntense interest and ongoing development of Dy-based SMMs demands gaining at horough understanding of their magnetic properties and thus requires am ultitechnique approach. [12] Since pentagonal-bipyramidal single-ion magnets are among the most attractive prototypes for high-performance SMMs, [28] we have selected the previously reported [29,30] mononuclear Dy III single-ion magnet, [Dy(Cy 3 PO) 2 -(H 2 O) 5 ]Br 3 ·2 (Cy 3 PO)·2 H 2 O·2 EtOH, (Cy 3 PO = tricyclohexyl phosphine oxide) (1), to measure the strength of the internal magnetic hyperfine field and to extract the magnetic moment in order to demonstrate the use of 161 Dy SMS on aS MM. [17] Conventional 161 Dy Mçssbauer spectroscopy has already been used to study magnetic hyperfine fields of Dy metal, [18] oxide [19,20] and alloys, [21,22] but it has not yet been used to investigate Dycontaining SMMs,i np art because,a lthough the naturally abundant (18.9 %) 161 Dy isotope is stable, [23] the necessary 161 Tb: 161 GdF 3 source has to be activated by neutron irradiation and 161 Tb has ah alf-life of only 6.9 days.…”

“…[1,2,6] Among the lanthanide ions,D yi ons in addition to Tb ions [7] are often chosen since they can lead to SMMs with record anisotropy barriers [8] and blocking temperatures up to 80 Ka sw ell as showing molecular magnetic hysteresis. [12][13][14] Thei ntense interest and ongoing development of Dy-based SMMs demands gaining at horough understanding of their magnetic properties and thus requires am ultitechnique approach. [11] Fori ron-containing SMMs 57 Fe Mçssbauer spectroscopy has also been used in order to determine local moments and spin-relaxation dynamics.…”

“…[9,10] Magnetic properties of molecular spin systems like SMMs are typically studied by alternating (ac) and direct current magnetic measurement methods,electron spin resonance,and nuclear magnetic resonance. [12,15,16] Herein, we report on establishing 161 Dy time-domain synchrotron Mçssbauer spectroscopy (SMS) as anovel spectroscopic tool to study magnetic properties in Dy-containing molecules and in particular in SMMs.T his technique,a lso called nuclear forward scattering (NFS), makes use of the 161 Dy nucleus as aprobe sensing the Dy magnetization via the hyperfine interactions,w hich are effective between the Dy electron shell and the 161 Dy nucleus. [12][13][14] Thei ntense interest and ongoing development of Dy-based SMMs demands gaining at horough understanding of their magnetic properties and thus requires am ultitechnique approach.…”

“…[17] Conventional 161 Dy Mçssbauer spectroscopy has already been used to study magnetic hyperfine fields of Dy metal, [18] oxide [19,20] and alloys, [21,22] but it has not yet been used to investigate Dycontaining SMMs,i np art because,a lthough the naturally abundant (18.9 %) 161 Dy isotope is stable, [23] the necessary 161 Tb: 161 GdF 3 source has to be activated by neutron irradiation and 161 Tb has ah alf-life of only 6.9 days. [12] Since pentagonal-bipyramidal single-ion magnets are among the most attractive prototypes for high-performance SMMs, [28] we have selected the previously reported [29,30] mononuclear Dy III single-ion magnet, [Dy(Cy 3 PO) 2 -(H 2 O) 5 ]Br 3 ·2 (Cy 3 PO)·2 H 2 O·2 EtOH, (Cy 3 PO = tricyclohexyl phosphine oxide) (1), to measure the strength of the internal magnetic hyperfine field and to extract the magnetic moment in order to demonstrate the use of 161 Dy SMS on aS MM. [23][24][25][26] Thef irst excited nuclear state of 161 Dy has an energy of 25.65 keV (E1 transition) and al ifetime of t % 42.0 ns, [17] allowing investigation of Dycontaining SMMs in atime window complementary to that of other methods such as ac susceptibility (10 À4 -10 s) [15,27] and high-field electron paramagnetic resonance (10 À11 s).…”