Muon spin relaxation investigation of tetranuclear iron(III)Fe4(OCH3)6(

Abstract

We present a study of the spin dynamics of Fe 4 ͑OCH 3 ͒ 6 ͑dpm͒ 6 single molecule magnet by means of SQUID magnetization and muon relaxation ͑ + SR͒ measurements. In longitudinal field + SR experiments performed at magnetic fields H = 200, 1000 Oe, the muon asymmetry P͑t͒ could be fitted by means of three components, the first constant, the second fast relaxing through a quasiexponential decay, and the third, the slowest relaxing, showing an exponential decay. The slowest muon relaxation rate studied as a function of temperature T displayed two structures, a broad peak at T ϳ 15/ 20 K and a shoulder at T Ͻ 5 K, both decreasing in amplitude and displacing toward higher temperatures as the field is increased. To mimic qualitatively the temperature behavior ͑T͒ at the investigated fields, we used a function expressed as the sum of two Bloembergen-Purcell-Pound ͑BPP͒-like laws, reproducing the mechanism of relaxation. The exponential data resulted well fitted by means of a heuristic model which takes into account two correlation times Ј and , related to the ground-state multiplet barrier ͑⌬Ј / k B = 7.25 K͒ and to the intermultiplet separation ͑⌬ / k B = 86.4 K͒ between S = 5 and S=4.

NMR and μ+SR detection of unconventional spin dynamics in Er(trensal) and Dy(trensal) molecular magnets

“…1, differently from what found in all other molecular nanomagnets previously investigated by these techniques. [23,[26][27][28][29][45][46][47][48][49] Indeed, the dependence of the height of the peak upon external magnetic field is opposite to the one predicted by Eq. 1.…”

“…The observation of a peak in the relaxation rate is a common occurrence for all the molecular magnets investigated previously by 1 H NMR or μ + SR [23,[26][27][28][29][45][46][47][48][49]. For those systems, the 1/T 1 (or λ) vs T plot could be fitted well by an expression derived from the general formula of Moriya for nuclear relaxation in paramagnets [30,31] (BPP function) based on the presence of a single correlation frequency:…”

Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3{NIT(C6H4OPh)}]: A μ+ spin relaxation study

“…However, it should be noted that, in general, the molecular magnetization dynamics, and consequently, the nuclear relaxation, are driven by a complex spectral density of the electronic spin fluctuations, where different correlation frequencies C i ¼ 1/s Ci may come into play. [27][28][29][30] To describe the temperature dependence of the muon longitudinal relaxation rate k interm (T), we used a phenomenological semiclassical model that follows from the general expression 31,32 …”

“…However, the data cannot be fitted with such a simple function. Thus, assuming that more than one correlation time can play a role in the magnetization dynamics, [27][28][29][30] for the k interm (T) data fitting we used a corrected BPP function assuming a rectangular distribution of correlation times s Ci , whose center value s follows the Arrhenius law s ¼ s 0 exp(D/k B T). 29,34 This simple distribution was chosen because the corrected BPP function has a closed analytical form, and, was found to fit k interm (T) quite well.…”