S = 1/2 Ising behavior in the two-dimensional molecular magnet Fe(NCS)₂(pyrazine)₂

The magnetic ordering and critical behavior of antiferromagnetic Fe NCS 2 pyz 2 has been studied by neutron powder dffraction NPD , inelastic neutron scattering INS , Mossbauer spectroscopy and magnetic measurements. The system can be regarded as a 2D antiferromagnet even in the ordered phase, given that long range magnetic ordering between the layers simply follows a necessary consequence of the establishment of long range ordering within the planes. The INS data, which were taken on a cold neutron time of flight spectrometer, reveals that when the temperature is lowered towards TN, the correlation length within the 2D layers increases and ultimately crosses over from two to three dimensional behavior. Indeed, 3D long range antiferromagnetic order, associated with a propagation vector [1,0, 1 4 e], is observed in the NPD data below 6.8K. Furthermore, in agreement with the behavior of both T and Cm T data, the order parameter follows the exact Osangersolution for a 2D S 1 2 Ising syste

A Novel Route to Toluene-Soluble Magnetic Oxide Nanoparticles: Aqueous Hydrolysis Followed by Surfactant Exchange

The ability of capped nanoparticles of inorganic materials to dissolve in nonpolar solvents such as toluene creates opportunities for size-selective precipitation, surface modification through covalent means, incorporation into polymer composites, and the possibility of digestive ripening. Toluene-soluble nanoparticles are usually prepared in nonpolar solvents, where they are capped by hydrophobic surfactants; such preparations often require specialized high-temperature solvents and expensive precursors. Many transition metal oxides are easily prepared in nanoparticulate form cheaply and in quantity, by hydrolysis in aqueous media. However, capping of nanoparticles in aqueous media to make them nonpolar is usually difficult. We present here a simple process of surfactant exchange that permits $\approx4-nm$ particles of the magnetic spinel oxides $MFe_2O_4$ (M = Mn and Zn) to be prepared in water in the presence of a surfactant and to then be transferred to toluene wherein the particles are capped by a second surfactant, a long-chain amine. The aminecapped nanoparticles can be successively precipitated and redissolved from their toluene solutions. Mo¨ssbauer spectroscopy and SQUID magnetization have been used to characterize magnetic properties of the nanoparticles

Magnetic Blocking in a Linear Iron(I) Complex

Single-molecule magnets that contain one spin centre may represent the smallest possible unit for spin-based computational devices. Such applications, however, require the realization of molecules with a substantial energy barrier for spin inversion, achieved through a large axial magnetic anisotropy. Recently, significant progress has been made in this regard by using lanthanide centres such as terbium(III) and dysprosium(III), whose anisotropy can lead to extremely high relaxation barriers. We contend that similar effects should be achievable with transition metals by maintaining a low coordination number to restrict the magnitude of the d-orbital ligand-field splitting energy (which tends to hinder the development of large anisotropies). Herein we report the first two-coordinate complex of iron(I), [Fe(C(SiMe3) 3)2]-, for which alternating current magnetic susceptibility measurements reveal slow magnetic relaxation below 29 K in a zero applied direct-current field. This S =complex exhibits an effective spin-reversal barrier of U eff = 226(4) cm-1, the largest yet observed for a single-molecule magnet based on a transition metal, and displays magnetic blocking below 4.5 K