Disorder in Molecular Magnets
Abstract
Disorder in molecular magnets is studied through magnetic, chemical, and crystallographic studies. The effect of solvent on the disordered molecular ferrimagnetic material V(TCNE)_{rm x} {cdot}y(solvent) (TCNE = tetracyanoethylene) is studied through the dc magnetization and ac susceptibility of the materials prepared by varying the solvent from among the group dichloromethane = CH_2Cl _2, tetrahydrafuran = C_4 H_8O, acetonitril = CH _3CN, and a mixture of acetonitril and benzene = C_6H_6. The use of these materials for inductive and magnetic shielding applications is discussed. A spin glass phase in the reentrant ferrimagnet V(TCNE)_{rm x} {cdot}y(CH_3CN) is studied in detail through static and dynamic magnetic susceptibility measurements, which illuminate the roles of random magnetic anisotropy and random exchange. Disorder in molecular magnets is studied further through the crystalline material MnTPP TCNE (TPP = meso tetraphenyl porphinato), which shows subtle rotational disorder in the TCNE orientation. This material is a reentrant ferrimagnet with T_ {c} ~ 18 K and T_{f} ~ 6.9 K. The field dependences of the magnetization and the freezing temperature follow the behavior for a mean field random exchange frustrated ferrimagnet. Dynamics at low field indicate that the relaxation is in the form of independently relaxing clusters which show activated dynamics over a temperature dependent barrier where the temperature dependence of the barrier is consistent with highly anisotropic spin glass droplets.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT.......106M
- Keywords:
-
- MAGNETS;
- FERRIMAGNETS;
- Physics: Condensed Matter; Physics: Electricity and Magnetism; Chemistry: Physical