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Human ferritin homopolymers with H or L subunits (rHF and rLF) were genetically engineered in E coli. Apoferritins were then reconstituted with 2000 Fe atoms. A big difference was observed in the rates of iron uptake, whereas the mean core size was similar in rHF and rLF. Magnetization of the recombinant human ferritins were measured as functions of temperature and field. The blocking temperature TB(H) at low fields is considerably higher in rLF than in rHF. From the fit of M(H) data to a modified Langevin function: M(H)=M0L(μpH/kBT)+χaH, the effective magnetic moment μp is found to be much larger in rLF than in rHF. Experimental data demonstrate that the magnetic properties, in particular, the uncompensated spins of ferritin core are related to the biomineralization process in ferritins. [ABSTRACT FROM AUTHOR]

We report ¹H and [sup 23]Na nuclear magnetic resonance (NMR) and relaxation measurements in two variants of the V6 cluster with formula [CH[sub 3]H[sub 6][sub 4]Na[sub 2][H[sub 4]{V[sub 3]L}[sub 2]P[sub 4]O[sub 4]]·14H[sub 2]O and Na[sub 6][H[sub 4]{V[sub 3]L}[sub 2]P[sub 4]O[sub 4]]· 18H[sub 2]O, respectively. Both the NMR linewidth and the spin-lattice relaxation (NSLR) data can be explained semiquantitatively by assuming a dipolar coupling between the proton (sodium) nuclei and the three V(IV) magnetic moments forming an almost equilateral triangle with nearest neighbor antiferromagnetic exchange interactions. From the temperature dependence of the [sup 23]Na NSLR we obtain the value of the two gaps separating the lower energy total spin states. [ABSTRACT FROM AUTHOR]

We report [sup 1]H nuclear magnetic resonance spin-lattice relaxation rate (NSLR) measurements as a function of temperature (1.5–4.2 K) and as a function of applied magnetic field (0.2–8.2 T) in the molecular magnet [(PhSiO[sub 2])[sub 6]Cu[sub 6](O[sub 2]SiPh)[sub 6]] in short Cu6. The results are explained in terms of a simple model whereby the NSLR is driven by the fluctuations of the local hyperfine field due to the reorientation of the total spin of the molecule in its ground state. From the analysis of the data, we infer the temperature and field dependence of the characteristic rate of the fluctuations of the total magnetization of the Cu6 ring in its ground state. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report 11B nuclear magnetic resonance (NMR) and zero-field muon spin relaxation (ZF-μSR) measurements of the anisotropic spin tetramer system CdCu2 (BO3)2, which consists of strongly interacting Cu(l) dimers and weakly coupled nonfrustrated Cu(2) spins. Long-range magnetic order is observed at TN = 9.8 K by a critical divergence of the nuclear spin-lattice relaxation rate 1/T1 and an appearance of well-defined muon-spin precessions. In addition, we find the spectroscopic signature for a magnetic anomaly at T* = 6.5 K, a few kelvins below TN. For temperatures below T*, 1/T1 ceases tofollow a T4.9(1) behavior. Instead, upon cooling below T*, both 1/T) and 1 /T2 become temperature-independent with a subsequent small drop. The muon frequency and the relative fraction of the Cu magnetic sites show anomalies mostly for Cu(2) spins at T*. This is ascribed to a Cu(2) spin reorientation. Site-specific change in magnetic structure is discussed in terms of the energy hierarchy of involved exchange interactions and an additional intertetramer interaction that controls magnetism at temperature T*. [ABSTRACT FROM AUTHOR]

We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba3IrTi2O9, which constitutes a distinct frustration motif made up of a mixture of edge- and corner-sharing triangles. In spite of a strong antiferromagnetic exchange interaction of the order of 100 K, we find no hint for long-range magnetic order down to 23 mK. The magnetic specific heat data unveil T-linear and T-squared dependences at low temperatures below 1 K. At the respective temperatures, the zero-field muon spin relaxation features a persistent spin dynamics, indicative of unconventional low-energy excitations. A comparison to the 4d isostructural compound Ba3RuTi2O9 suggests that a concerted interplay of compasslike magnetic interactions and frustrated geometry promotes a dynamically fluctuating state in a triangle-based iridate. [ABSTRACT FROM AUTHOR]