High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

Abstract

Articles you may be interested inHigh temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac) 3 NITEt and the magnetically frustrated Gd(hfac) 3 NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr 8 closed ring and in Cr 7 Cd and Cr 8 Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime. V C 2015 AIP Publishing LLC.[http://dx

Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings

“…One particular situation of interest in the present work is when the homometallic ring is interrupted by the presence of a diamagnetic metal ion, as in the case of Cr 8 Cd, 17 recently investigated by polarized neutron diffraction. 18 Another example is [Cr 8 [18][19][20] The structure of Cr 8 Zn is referred to as an "open ring," composed by eight Cr 3+ (s = 3/2) ions and one Zn 2+ diamagnetic ion, with S = 0 ground state. A previous study on this compound was done by means of Inelastic Neutron Scattering (INS) measurements performed on a randomly oriented microcrystalline sample.…”

NMR Study of Spin Dynamics in V7Zn and V7Ni Molecular Rings

“…Moreover, when by diminishing T the characteristic frequency of the magnetization fluctuations reaches a value of the order of the nuclear Larmor frequency ω L , the NSLR diplays a maximum followed by a subsequent decrease when the temperature is further lowered. This behavior, including a peak in NSLR, has been observed in all the MNMs and magnetic rings investigated so far [13,14]. However, the magnetic rings investigated are all made up of semi-integer spins and thus it seems of interest to investigate integer spin rings like V 7 Zn and V 7 Ni to see if any difference in the spin dynamics can be detected.…”

“…3b. When one compares the results for the two integer vanadium rings with the results in rings of semi-integer spins [13,14], e.g., Cr8, Fe6, Fe10, Cr7Cd and Cr8Zn, one finds that the results are similar except for the lower cutoff field observed in the vanadium rings. The lower cutoff field in V rings could be due to the different local anisotropy of V 2+ ions with respect to, e.g., Cr 2+ ions, and/or the difference between the spin values, i.e., s = 1 for V 2+ ions and s = 3/2 for Cr 2+ ions, and/or a different intermolecular interaction.…”

“…The first spin dynamics model is the one describing the CF of the vanadium spins with an initial fast decaying component determined by the strong exchange interaction J, followed by a plateau in the CF and a cutoff function whose FT in the frequency domain, S(ω), is approximated by a Lorentzian function of width ω cutoff . The NSLR, which is proportional to the FT S(ω L ) of the CF, can then be expressed as [13,14]: Table 1. The solid lines are the best fits according to the 1D spin diffusion model, i.e., Equation 2, with the set of fitting parameters listed in Table 2; b the data are plotted as a function of the inverse square root of the applied magnetic field.…”

“…In this paper, we present and discuss only the results of 1 H nuclear magnetic resonance and relaxation in the V 7 Ni and V 7 Zn rings. A large body of literature describing the spin dynamics obtained by NMR in magnetic molecules [13,14] and in particular in the semi-integer spin ring systems exists [15][16][17][18][19][20]. In contrast, the importance of spin dynamics in integer spin ring systems has not been well recognized by the NMR community, and no paper, to our knowledge, has been published.…”