Low magnetic moment PIN diodes for high field MRI surface coils.

Positive-intrinsic-negative (PIN) silicon diodes are commonly used in magnetic resonance imaging (MRI) coils to perform active or passive blocking and detuning, or to disable circuit functions. However, diode packages with large magnetic moments are known to cause image artifacts in high field MRI systems. In this study, diode packages with low magnetic moment were designed by compensating components of ferromagnetic nickel and paramagnetic tungsten with diamagnetic silver. The new diodes have an initial positive susceptibility up to fields of 1 T and a negative susceptibility from 1 to 7 T. Their magnetic moments are one to two orders of magnitude smaller than those of standard diodes; moments as small as 20 nJ/T at 7 T were achieved.

Solution and Solid State Properties of [N-(2-Hydroxyethyl)iminodiacetato]vanadium(IV), -(V), and -(IV/V) Complexes(1).

A mononuclear vanadium(IV), a mononuclear vanadium(V), and a binuclear mixed valence vanadium(IV/V) complex with the ligand N-(2-hydroxyethyl)iminodiacetic acid (H(3)hida) have been structurally characterized. Crystal data for [VO(Hhida)(H(2)O)].CH(3)OH (1): orthorhombic; P2(1)2(1)2(1); a= 6.940(2), b = 9.745(3), c= 18.539(4) Å; Z = 4. Crystal data for Na[V(O)(2)(Hhida)(2)].4H(2)O (2): monoclinic; P2(1)/c; a = 6.333(2), b = 18.796(2), c = 11.5040(10) Å; beta = 102.53(2) degrees; Z = 4. Crystal data for (NH(4))[V(2)(O)(2)(&mgr;-O)(Hhida)(2)].H(2)O (3): monoclinic; C2/c; a = 18.880(2), b= 7.395(2), c = 16.010(2) Å; beta = 106.33(2) degrees; Z = 4. The mononuclear vanadium(IV) and vanadium(V) complexes are formed from the monoprotonated Hhida(2)(-) ligand, and their structural and magnetic characteristics are as expected for six-coordinate vanadium complexes. An interesting structural feature in these complexes is the fact that the two carboxylate moieties are coordinated trans to one another, whereas the carboxylate moieties are coordinated in a cis fashion in previously characterized complexes. The aqueous solution properties of the vanadium(IV) and -(V) complexes are consistent with their structures. The vanadium(V) complex was previously characterized; in the current study structural characterization in the solid state is provided. X-ray crystallography and magnetic methods show that the mixed valence complex contains two indistinguishable vanadium atoms; the thermal ellipsoid of the bridging oxygen atom suggests a type III complex in the solid state. Magnetic methods show that the mixed valence complex contains a free electron. Characterization of aqueous solutions of the mixed valence complex by UV/vis and EPR spectroscopies suggests that the complex may be described as a type II complex. The Hhida(2)(-) complexes have some similarities, but also some significant differences, with complexes of related ligands, such as nitrilotriacetate (nta), N-(2-pyridylmethyl)iminodiacetate (pmida), and N-(S)-[1-(2-pyridyl)ethyl]iminodiacetate (s-peida). Perhaps most importantly, the mixed valence Hhida(2)(-) complex is significantly less stable than the corresponding pmida and s-peida complexes of similar overall charge but very similar in stability to the nta and V(2)O(3)(3+) complexes with higher charges. Thus, there is the potential for designing stable mixed valence dimers.