Curie behavior

A recent theoretical analysis of the temperature dependence of the magnetic response of neutral disorder-induced solitons 69], has revealed that these solitons may explain the low-temperature deviation from Curie behavior that is observed in experiments on Durham /ra/t.y-polyaeetylene [70]. A more stringent test of the theory would involve extending these experiments to even lower temperatures (down to 1 K or lower). 

Four strongly downshifted signals in each spectrum, between 50 and 110 ppm, were assigned to the four CB protons of the cysteines coordinating the Fe ". The contact shifts of the protons reflect the coordination of cysteine to the Fe " of the antiferromagnetically coupled Fe "-Fe" pair as the cysteine protons sense the spin down orientation of the Fe " (S = ) site. This is supported by the observation that the temperature dependence of the cysteine H" protons (measured between 276 and 308 K) follows Curie behavior (decreasing contact shift with increasing temperature). 

The temperature dependence of the molar magnetic susceptibility (x) of an assembly of paramagnetic spins without interaction is characterized by the Curie behavior with x = C/T where C = /Vy2( 2.S (.S + l)/3k. It is a very common situation in the organometallic chemistry of radical species when the spin density is essentially localized on the metal atom. Since, in most cases, this atom is surrounded by various innocent ligands, intermolecular interactions are very weak and in most cases are reflected by a small contribution described by a Curie-Weiss behavior, with x = C/(T 0) where 0 is the Curie-Weiss temperature. A positive value for 0 reflects ferromagnetic interactions while a negative value — the most common situation — reflects an antiferromagnetic interaction. 

A simple electrostatic model facilitates understanding the physical meaning of the Curie behavior of [Mn(taa)] in the HS phase. Electric polarization P produced by a number of reorienting molecular dipoles /r under a local field Eloc obeys a simple Curie law,... 

Magnetic susceptibility measurements in the 1-300 K range show that both EG and DG exhibit Curie behavior. The susceptibility values of EG and DG at 300 K are —3.5 x 10-6 and —4.4 x 10-6 emu g-1. These data are comparable to those reported by Andersson el al.s... 

The ccnplete absence of low-temperature Curie behavior in our ITF-TCNQ samples... 

Most of the lanthanide porphyrin complexes are paramagnetic, except those of lanthanum and lutetium which are diamagnetic. They all show paramagnetic behaviors in the NMR spectra similar to those of the lanthanide 0-diketonate complexes, except that the shift capabilities are less.4 Some of these paramagnetic lanthanide complexes (i.e., that of ytterbium) show Curie behavior at low temperature. Diamagnetic lutetium shows some ring current phenomena.4... 

---