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The magnetic behaviors of the metamagnetic and ferromagnetic phases of [Fe(C5Me5)2][TCNQ] (TCNQ = 7,7,8,8-tetracyano-p-quinodimethane). Determination of the phase diagram for the metamagnetic phase

AutorPalacio, Fernando
Fecha de publicaciónabr-2006
EditorRoyal Society of Chemistry (Great Britain)
CitaciónJournal of Materials Chemistry 16(26): 2677-2684 (2006)
ResumenThe detailed magnetic behaviors of the ferro- (1FO) and metamagnetic (1MM) phases of [FeCp*2][TCNE] (Cp* = pentamethylcyclopentadienide; TCNE = tetracyanoethylene) aligned parallel to the applied magnetic field, H, were obtained using eicosane (E). The Tc for 1FO is 3.1 K from the maximum in the frequency independent (T) data and 3.0 K from the maximum in the Cp(T) data, and exhibits a hysteresis with a coercive field, Hcr, 50 Oe, a remanent magnetization of 1900 emu Oe mol–1 at 2 K, and saturation magnetization of 16740 emu Oe mol–1. Significant differences were observed between aligned 1MM (1MM + E) and unaligned samples. Metamagnetic 1MM + E saturates to 15900 emu Oe mol–1, and has a 1300 Oe critical field at 2 K that decreases with increasing temperature. The 2 K M(H) of 1MM + E displays a small bump between |3000 and 4000| Oe that is not observed in 1MM. The Tc for 1MM + E is 2.5 ± 1 K from the maximum in the frequency independent (T) data, and peak maximum in Cp(T) data. The lack of a (T) response for H = 0 is in accord with 1MM + E having an antiferromagnetic ground state. Upon application of an applied field a (T) signal appears and increases in intensity until 1500 Oe in accord with 1MM + E going from an antiferromagnetic to a ferromagnetic-like state. For H > 1500 Oe the (T) signal decreases. In contrast to 1MM, between 2.2 and 2.8 K (H) and (H) exhibit peaks between 3000 and 4000 Oe. The temperature at which the peak maximum in Cp(T) occurs (2.4 K) for 1MM and is unexpectedly independent of H. The peak maxima observed in (T,H) at 100 and 1000 Hz were use to construct a magnetic phase diagram, H(T), for metamagnet 1MM + E, which has three different magnetic phases: paramagnetic, antiferromagnetic, and an intermediate phase. The detailed magnetic characterization of the structurally similar 1MM and 1FO phases will provide a basis for theorists to understand the subtle spin exchange interactions that lead not only to magnetic ordering, but the type of the ordering.
Descripción8 pages, 11 figures.-- This article is part of a themed issue on Molecular Magnetic Materials.-- et al.
Versión del editorhttp://dx.doi.org/10.1039/b603016e
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