Brian G. Morin

Spin frustration and metamagnetic behavior in a molecular-based quasi-1D ferrimagnetic chain: (MnTPP)(TCNE)

We report an experimental observation of spin frustration and metamagnetic behavior in a quasi‐1D ferrimagnetic chain, (MnTPP)+(TCNE)−. Metastability, hysteresis effects, and irreversibility of thermal and magnetic histories are observed in magnetization measurements. The ‘‘memory’’ phenomenon is seen in the temperature dependence of the thermoremanent and isothermal remanent magnetization. This system may be relevant to the magnetic behavior of the quantum/classical spin chains. The isothermal M(H) at T=2.25 K supports a first order transition which may be related to effects of local anisotropy.

Molecular magnets V(tetracyanoethylene)x⋅y(solvent): Applications to magnetic shielding

The specific advantages and limitations of a new class of polymer based magnets [exemplified by V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene)] for static and low frequency magnetic shielding and inductive applications are evaluated using results of dc superconducting quantum interference device magnetization and ac permeability measurements. Present materials have very low density (ρ∼1 g/cm3), relatively high resistivity (∼104 Ω cm), and low power loss (as low as ∼2 erg cm−3 cycle−1). The highest initial room temperature permeability observed to date (for solvent=CH2Cl2) of μi=13 is modest for practical applications. Flexible processing methods are suggested for optimization of magnetic properties important for shielding applications.

Complex ac susceptibility studies of the disordered molecular based magnets V(TCNE)x: Role of spinless solvent

The effect of different spinless solvents on the magnetism of V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene) is studied by temperature (T) dependent ac susceptibility above 2.3 K. Though V(TCNE)x⋅y(CH2Cl2) has a critical temperature Tc ∼400 K, for V(TCNE)x⋅y(C4H8O), Tc ∼205 K and the coercive field is reduced, while for V(TCNE)x⋅y(CH3CN), Tc ∼140 K or below and a spin glass phase exists below a spin freezing temperature of Tf∼7–15 K. The variations with solvent are suggested to be due to spin dilution and random anisotropy introduced by the spinless solvents.

Magnetization and dynamics of reentrant ferrimagnetic spin-glass [MnTPP]::+[TCNE].- ·2PhMe

We present direct current (dc) magnetization M(T,H) and alternating current (ac) susceptibility χac(T,H,f) data for the quasi‐one‐dimensional molecule‐based ferrimagnet [MnTPP]::+[TCNE].−⋅2PhMe (TPP=meso‐tetraphenylporphyrinato, TCNE=tetracyanoethylene). Static scaling of the real part χ′ of the ac susceptibility and data collapse of M(T,H) over a limited reduced temperature range above Tc≊13 K lead to the critical exponents γ≊1.6, β≊0.5, and δ≊4.2. Below Tc, χac depends sensitively on frequency and exhibits a striking double‐peak structure similar to that found in reentrant spin glasses. Possible models for the frequency dependence of the peaks observed in χac are discussed.