Fe3Se4 nanostructures have been synthesized by a one-pot high-temperature organic-solution-phase method. The size of these nanostructures can be tuned from 50 to 500 nm, and their shapes can be varied from nanosheets and nanocacti to nanoplatelets. These nanostructures exhibit hard magnetic properties, with giant coercivity values reaching 40 kOe at 10 K and 4 kOe at room temperature. The estimated magnetocrystalline anisotropy constant is 6 × 106 erg cm–3, comparable to that of hexagonal close-packed cobalt. The magnetic properties can be further tuned by substituting Fe ions by other transition-metal elements such as Co.

The hard magnetic properties of Fe3Se4 nanostructures were studied both experimentally and theoretically. Magnetic measurements showed that Fe3Se4 nanoparticles can exhibit giant coercivity exceeding 40 kOe at low temperature (10 K). This unusually large coercivity is attributed to the uniaxial magnetocrystalline anisotropy of the monoclinic structure of Fe3Se4 with ordered cation vacancies. The measured anisotropy constant is 1.0 × 107 erg/cm3, consistent with the result from first-principles calculations. The magnetization reversal mechanism of the nanoparticles is found to be incoherent spin rotation.

Carrier-dopant exchange interactions in Mn-doped PbS colloidal quantum dots were studied by circularly polarized magneto-photoluminescence. Mn substitutional doping leads to paramagnetic behavior down to 5 K. While undoped quantum dots show negative circular polarization, Mn doping changes its sign to positive. A circular polarization value of 40% was achieved at T=7 K and B=7 tesla. The results are interpreted in terms of Zeeman splitting of the band edge states in the presence of carrier-dopant exchange interactions that are qualitatively different from the s,p-d exchange interactions in II-VI systems.

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The new ligand, tris(5-methylpyrazolyl)methane (1), has been prepared by the reaction of n-butyl lithium with tris(pyrazolyl)methane followed by trimethylation of the tetralithiated species with methyl iodide. The BF(4)(-), ClO(4)(-), and BPh(3)CN(-) salts of the Fe(II) complex of this ligand were also synthesized. The X-ray crystal structure of the BF(4)(-) complex (2) at 100 K had Fe-N bond lengths of 1.976 Å, indicative of a low spin Fe(II) complex, while at room temperature, the structure of this complex had a Fe-N bond distance close to 2.07 Å, indicative of an admixture of approximately 50% low-spin and 50% high-spin. The solid-state structure of the complex with a ClO(4)(-) counterion was determined at 5 different temperatures between 173 and 293 K, which allowed the thermodynamic parameters for the spin-crossover to be estimated. Mössbauer spectra of the BF(4)(-) complex further support spin-state crossover in the solid state with a transition temperature near 300 K. UV-visible spectroscopy and (1)H NMR studies of 2 show that the transition temperature in solution is closer to 400 K. No spin-crossover was observed for [Fe(1)(2)](2+)·2BPh(3)CN(-). The results allow the separation of effects of groups in the 3-position from those in the 5-position on tpm ligands, and also point toward a small cooperative effect in the spin-crossover for the Fe(II) complex.