Magnetic order of FeCl3 and CoCl2-graphite intercalation compounds by neutron diffraction

Magnetic phase diagram and cluster glasslike properties of stage-1 graphite-intercalated FeCl3

“…Below 80 K, the inverse susceptibility starts to deviate from the Curie-Weiss behavior in a continuous fashion, indicating an increase of both the effective magnetic moment and the antiferromagnetic character of the interactions with decreasing temperature. These observations indicate the onset of short-range order and are consistent with PND results [12], according to which short-range magnetic correlations gradually build up below 30 K in this system. Table I compares our Curie-Weiss law parameters with those reported in the literature.…”

“…The analysis of the magnetic diffraction peak shapes shows that this transition corresponds to a crossover from a 2D to 3D ordering [10,12]. Indeed, whereas the peak shapes are symmetric below 3.8 K, as expected for 3D long-range ordering, they become asymmetric above 3.8 K, adopting Warren-type shapes characteristic of powder patterns of 2D systems.…”

“…Warren-type asymmetric peak shapes have been reported at all temperatures for the β-type stage-2 compounds [12]. Thus, in this system, the magnetic correlations are strictly 2D in nature, although they can be described using the same modulation vector as for the stage-1 compound [12]. Both stage-2 and stage-3 compounds show spin-glass-like behavior [8].…”

“…This transition has only been observed when a magnetic field is applied in the basal plane and is suppressed when μ 0 H 1 mT [9]. The β-type GICs exhibit an antiferromagnetic phase transition at temperatures varying between 3.6 and 5.5 K for stage-1 compounds [10,12]. As the intercalant (FeCl 3 ) is extremely hygroscopic, it has been hypothesized that the intercalated α-type can react with water in the air, creating the β-type variant [10].…”

“…Powder neutron diffraction (PND) experiments showed that the stage-1 α-type compounds order magnetically at 1.7 K in a configuration that can be described by an in-plane modulation vector of Q = 0.25 a * and Q ≈ 0.3 Å −1 [10], where a * is the reciprocal in-plane parameter of the iron lattice. On the other hand, the stage-1 β-type compounds undergo a magnetic phase transition at 3.8 K to a low-temperature 3D long-range ordered phase characterized by an in-plane incommensurate modulation with a vector Q = 0.394 a * and Q ≈ 0.467 Å −1 [10,12].…”