Gadolinium as an accelerator for reaching thermal equilibrium and its influence on the ground state of Dy2GdN@C80 single-molecule magnets

Abstract

Endohedral fullerenes are perfect nanolaboratories for the study of magnetism. The substitution of a diamagnetic scandium atom in Dy 2 ScN@C 80 with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M 4,5 edges of Gd and Dy shows that Gd affects the ground state. The Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy 2 ScN@C 80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes the faster equilibration in Dy 2 GdN@C 80 . This sheds light on the importance of angular momentum balance and symmetry in magnetic relaxation.

Precise measurement of angles between two magnetic moments and their configurational stability in single-molecule magnets

“…Figure 4(b) shows the extracted relaxation times (see Supplemental Material [23]) from which kinetic barriers of ScN eff = 0.65 meV and TiC eff = 0.82 meV are obtained. The value of 0.65 meV for Dy 2 ScN@C 80 is close to that of eff = 0.73 meV [13] and 0.77 meV [38] from previous studies, and again lower than that of Dy 2 TiC@C 80 . The prefactors or interception points with 1/T=0 in the Arrhenius plot, τ 0 , get 5.1 and 70.8 s, for Dy 2 TiC@C 80 and Dy 2 ScN@C 80 , respectively.…”

“…To compare the two systems, we adopt the pseudospin model previously applied to the ground state of the nitride cluster fullerene SMMs Dy 2 ScN@C 80 [13], Dy 2 GdN@C 80 [38], and Tb 2 ScN@C 80 [39]. Here, each moment can take two antiparallel directions along the magnetic easy axis, resulting in 2 2 possible arrangements, grouped into two degenerate time-reversal symmetric doublets, where the ground state corresponds to the FM configuration |1 and | 1 , see Fig.…”

“…exhibits distinct minima from which θ mag = 117.1 ± 0.2 • for Dy 2 ScN@C 80 and θ mag = 115.2 ± 0.7 • for Dy 2 TiC@C 80 are determined by fitting quadratic function χ 2 (θ ) = χ 2 min + A(θ − θ 0 ) 2 . The accuracy of the angles were estimated from δθ ∼ N p / √ N − 1 χ 2 min /A where N p = 3 is the number of fit parameters, N = 120 the number of data points, and A the curvature [38]. To relate the finding of the different angles between the magnetic moments of the Dy ions in Dy 2 ScN@C 80 and Dy 2 TiC@C 80 with their calculated molecular structures, we first analyzed the distribution of Dy − N − Dy and Dy − C − Dy angles θ bond .…”

“…The prefactors or interception points with 1/T=0 in the Arrhenius plot, τ 0 , get 5.1 and 70.8 s, for Dy 2 TiC@C 80 and Dy 2 ScN@C 80 , respectively. This is another important indicator for the magnetic stability [38], although it is particularly difficult to predict.…”

Энергетический спектр и оптические свойства фуллерена C-=SUB=-80-=/SUB=-(I-=SUB=-h-=/SUB=-) в модели Хаббарда

“…Отметим, что в фуллерене C 60 все атомы углерода эквивалентны. Исследованию свойств фуллерена C 80 посвящено довольно много работ [7][8][9].…”