Graphite Bi-intercalation Compound Research Articles

Stretched-exponential relaxation in the three-dimensional short-range Ising spin-glassCu0.5Co0.5Cl2-FeCl3graphite bi-intercalation compound

${\text{Cu}}_{0.5}{\text{Co}}_{0.5}{\text{Cl}}_{2}{\text{-FeCl}}_{3}$ graphite bi-intercalation compound is a three-dimensional short-range spin glass with a spin freezing temperature ${T}_{\text{SG}}$ $(=3.92\ifmmode\pm\else\textpm\fi{}0.11\text{ }\text{K})$. The time evolution of the zero-field-cooled magnetization ${M}_{\text{ZFC}}(t)$ has been measured under various combinations of wait time $({t}_{w})$, temperature $(T)$, temperature shift $(\ensuremath{\Delta}T)$, and magnetic field $(H)$. The relaxation rate ${S}_{\text{ZFC}}(t)$ $[=(1/H)d{M}_{\text{ZFC}}(t)/d\text{ }\text{ln}\text{ }t]$ shows a peak at a peak time ${t}_{\text{cr}}$. The shape of ${S}_{\text{ZFC}}(t)$ in the vicinity of ${t}_{\text{cr}}$ is well described by stretched exponential relaxation (SER). The SER exponent $b$ and the SER relaxation time ${\ensuremath{\tau}}_{\text{SER}}$ are determined as a function of ${t}_{w}$, $T$, $H$, and $\ensuremath{\Delta}T$. The value of $b$ at $T={T}_{\text{SG}}$ is nearly equal to 0.3. There is a correlation between ${\ensuremath{\tau}}_{\text{SER}}$ and $1/b$, irrespective of the values of ${t}_{w}$, $T$, $H$, and $\ensuremath{\Delta}T$. These features can be well explained in terms of a simple relaxation model for glassy dynamics.

Aging dynamics across a dynamic crossover line in the three-dimensional short-range Ising spin-glassCu0.5Co0.5Cl2−FeCl3graphite bi-intercalation compound

Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ graphite intercalation compound is a three-dimensional short-range Ising spin glass with a spin freezing temperature $T_{c}$ ($= 3.92 \pm 0.11$ K). The stability of the spin glass phase in the presence of a magnetic field $H$ is examined from (i) the spin freezing temperature $T_{f}(\omega,H)$ at which the differential field-cooled (FC) susceptibility $\partial M_{FC}(T,H)/\partial H$ coincides with the dispersion $\chi^{\prime}(\omega,T,H=0)$ with the angular frequency $\omega$, and (ii) the time dependence of zero-field cooled (ZFC) susceptibility $\chi_{ZFC}$ after a ZFC aging protocol with a wait time $t_{W}$ ($= 1.0 \times 10^{4}$). The relaxation rate $S(t)$ (= d$\chi_{ZFC}$/d$\ln t$) exhibits a local maximum at a characteristic time $t_{cr}$, reflecting non-equilibrium aging dynamics. The peak time $t_{cr}(T,H)$ decreases with increasing $H$ at the fixed temperature $T$ (2.9 K $\leq T<T_{c}$). The spin freezing temperature $T_{f}(\omega,H)$ provides evidence for the instability of the spin glass phase in thermal equilibrium in a finite magnetic field. Both $t_{cr}(T,H)$ and $T_{f}(\omega,H)$ exhibit certain scaling behavior predicted from the droplet picture, suggesting a dynamic crossover from SG dynamics to paramagnetic behavior in the presence of $H$.

Aging dynamics in a reentrant ferromagnet:Cu0.2Co0.8Cl2−FeCl3graphite bi-intercalation compound

The aging dynamics of a reentrant ferromagnet ${\mathrm{Cu}}_{0.2}{\mathrm{Co}}_{0.8}{\mathrm{Cl}}_{2}\ensuremath{-}\mathrm{Fe}{\mathrm{Cl}}_{3}$ graphite bi-intercalation compound has been studied using ac and dc magnetic susceptibility. This compound undergoes successive transitions at the transition temperatures ${T}_{c}$ $(=9.7\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and ${T}_{\mathit{RSG}}$ $(=3.5\phantom{\rule{0.3em}{0ex}}\mathrm{K})$. The relaxation rate $S(t)$ $[=\mathrm{d}{\ensuremath{\chi}}_{\mathit{ZFC}}(t)∕\mathrm{d}\phantom{\rule{0.2em}{0ex}}\mathrm{ln}\phantom{\rule{0.2em}{0ex}}t]$ exhibits a characteristic peak at ${t}_{\mathit{cr}}$ close to a wait time ${t}_{W}$ below ${T}_{c}$, indicating that the aging phenomena occur in both the reentrant spin glass phase below ${T}_{\mathit{RSG}}$ and the ferromagnetic (FM) phase between ${T}_{\mathit{RSG}}$ and ${T}_{c}$. The aging state in the FM phase is fragile against a weak magnetic-field perturbation. The time $(t)$ dependence of ${\ensuremath{\chi}}_{\mathit{ZFC}}(t)$ around $t\ensuremath{\approx}{t}_{\mathit{cr}}$ is well approximated by a stretched exponential relaxation, ${\ensuremath{\chi}}_{\mathit{ZFC}}(t)\ensuremath{\approx}\mathrm{exp}[\ensuremath{-}{(t∕\ensuremath{\tau})}^{1\ensuremath{-}n}]$, around $t={t}_{W}$. The exponent $n$ depends on ${t}_{W}$, $T$, and $H$. The relaxation time $\ensuremath{\tau}$ $(\ensuremath{\approx}{t}_{\mathit{cr}})$ exhibits a local maximum around $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, reflecting a frustrated nature of the FM phase. It drastically increases with decreasing temperature below ${T}_{\mathit{RSG}}$.

Nonlinear magnetic susceptibility and aging phenomena in a reentrant ferromagnet:Cu0.2Co0.8Cl2−FeCl3graphite bi-intercalation compound

Linear and nonlinear dynamic properties of a reentrant ferromagnet Cu$_{0.2}$Co$_{0.8}$Cl$_{2}$-FeCl$_{3}$ graphite bi-intercalation compound are studied using AC and DC magnetic susceptibility. This compound undergoes successive phase transitions at the transition temperatures $T_{h}$ (= 16 K), $T_{c}$ (= 9.7 K), and $T_{RSG}$ (= 3.5 K). The static and dynamic behaviors of the reentrant spin glass phase below $T_{RSG}$ are characterized by those of normal spin glass phase with critical exponent $\beta$ = 0.57 $\pm$ 0.10, a dynamic critical exponent $x$ = 8.5 $\pm$ 1.8, and an exponent $p$ (= 1.55 $\pm$ 0.13) for the de Almeida -Thouless line. A prominent nonlinear susceptibility is observed between $T_{RSG}$ and $T_{c}$ and around $T_{h}$, suggesting a chaotic nature of the ferromagnetic phase ($T_{RSG} \leq T \leq T_{c}$) and the helical spin ordered phase ($T_{c} \leq T \leq T_{h}$). The aging phenomena are observed both in the RSG and FM phases, with the same qualitative features as in normal spin glasses. The aging of zero-field cooled magnetization indicates a drastic change of relaxation mechanism below and above $T_{RSG}$. The time dependence of the absorption $\chi^{\prime \prime}$ is described by a power law form ($\approx t^{-b^{\prime \prime}}$) in the ferromagnetic phase, where $b^{\prime \prime} \approx 0.074 \pm 0.016$ at $f$ = 0.05 Hz and $T$ = 7 K. No $\omega t$-scaling law for $\chi^{\prime \prime}$ [$\approx (\omega t)^{-b^{\prime \prime}}$] is observed.

Structural Study of a Novel Graphite Bi-Intercalation Compound

Novel graphite biintercalation compound with layers of SmCl3 and ErCl3 is synthetized by the one-zone vapour method. A well defined stage-3 SmCl3 graphite intercalation compound with the c-axis repeat distance Ic = 16.60 ± 0.07 Å is used as the host matrix. The X-ray diffraction shows a creation of a new compound with Ic= 19.70 ± 0.05Å. Based on these data a … G-SmCl3 -G-ErCl3… stacking sequence is proposed. The electron diffraction shows a-axis of the intercalated layer is rotated with respect to the graphene a-axis by 42°, and 19°, 42° for SmCl3 and ErCl3 layers, respectively. The parameters of the lattices obtained are aSmC13 =7.37 Å, aErCl3 = 6.75 Å, and bErC13 = 11.73 Å.

Successive magnetic phase transitions of aCoCl2−FeCl3graphite bi-intercalation compound

${\mathrm{CoCl}}_{2}{\ensuremath{-}\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3}$ graphite bi-intercalation compound (GBIC) has a c-axis stacking sequence of ${\ensuremath{-}G\ensuremath{-}I}_{1}{\ensuremath{-}G\ensuremath{-}I}_{2}{\ensuremath{-}G\ensuremath{-}I}_{1}{\ensuremath{-}G\ensuremath{-}I}_{2}\ensuremath{-}G\ensuremath{-}$ $(G=\mathrm{graphite}\mathrm{}\mathrm{layer},$ ${I}_{1}={\mathrm{CoCl}}_{2}\mathrm{}\mathrm{layer},$ and ${I}_{2}={\mathrm{FeCl}}_{3}\mathrm{}\mathrm{layer}).$ This compound undergoes four magnetic phase transitions at ${T}_{h}(=16.4\mathrm{K}),$ ${T}_{\mathrm{cu}}(=8.5--8.7\mathrm{K}),$ ${T}_{\mathrm{cl}}(=7.3--7.4\mathrm{K}),$ and ${T}_{\mathrm{SG}}(=4.7--5.9\mathrm{K}).$ The static and dynamic aspects of spin orderings in this compound have been studied employing the temperature, frequency, and field dependence of dispersion ${\ensuremath{\chi}}_{\mathrm{aa}}^{\ensuremath{'}}$ and ${\ensuremath{\chi}}_{\mathrm{cc}}^{\ensuremath{'}},$ and the absorption ${\ensuremath{\chi}}_{\mathrm{aa}}^{\ensuremath{''}}$ and ${\ensuremath{\chi}}_{\mathrm{cc}}^{\ensuremath{''}}.$ A possible helical spin order occurring below ${T}_{h}$ is due to the spin frustration effect arising from competing interplanar exchange interactions. Below ${T}_{\mathrm{cu}}$ two-dimensional (2D) ferromagnetic long-range order appears in each ${\mathrm{CoCl}}_{2}$ layer. Below ${T}_{\mathrm{cl}}$ these 2D ferromagnetic ${\mathrm{CoCl}}_{2}$ layers are antiferromagnetically stacked along the c axis, forming a three-dimensional (3D) antiferromagnetic phase. The spin-glass phase occurring in each ${\mathrm{FeCl}}_{3}$ layer below ${T}_{\mathrm{SG}}$ is due to the spin frustration effect arising from competing intraplanar exchange interactions between majority XY ${\mathrm{Fe}}^{3+}$ spins and minority Ising ${\mathrm{Fe}}^{2+}$ spins. The phase transitions near ${T}_{\mathrm{cu}},$ ${T}_{\mathrm{cl}},$ and ${T}_{\mathrm{SG}}$ are partially destroyed by random fields generated in ${\mathrm{FeCl}}_{3}$ layers and ${\mathrm{CoCl}}_{2}$ layers, respectively, through competing interplanar exchange interactions.

Structural transitions in the graphite-AlCl 3-FeCl 3 system

X-ray, electron diffraction and electron energy loss spectroscopy reveal the transition process of the stage and basal-plane structures in the graphite-AlCl 3-FeCl 3 system reaction between stage-2 FeCl 3-GMIC (graphite monointercalation compound) and gaseous aluminum(III) chloride (AlCl 3). The intercalant iron(III) chloride (FeCl 3) is replaced by the intercalated AlCl 3 even at 150°C, and finally the FeCl 3-GMIC changes into stage-1 AlCl 3-GMIC. In the intermediate stage of this process, the synthesized compound has an alternative stacking of the intercalant FeCl 3 and AlCl 3, layers, which corresponds to the stage structure of AlCl 3-FeCl 3-GBIC (graphite biintercalation compound). In this transition process, the basal-plane structure of intercalant FeCl 3 maintains its original structure until the intercalant FeCl 3 deintercalates completely. As for the intercalant AlCl 3, the basal-plane structure of the microcrystalline state appears in the early stage of this reaction. The microcrystals expand the galleries between graphite layers as pillars, so that the repeat distance of the compound is the same as that of GBIC even if the concentration of the intercalant AlCl 3 is low. The structure of the microcrystal turns into the rectangular structure with a well-defined orientation to graphite lattice as the intercalation of AlCl 3 proceeds. These basal-plane structures of the intercalant AlCl 3 can also be observed in AlCl 3-GMIC. The GBIC is not homogeneous on the micrometer scale. The cause of deintercalation of FeCl 3 is discussed from the viewpoint of AlFeCl 6 complex formation.

Magnetism of a graphite bi-intercalation compound with two types of ferromagnetic layers: double hysteretic transition in CrCl3–NiCl2–C

An atomic-scale multilayer with two types of ferromagnetic layers is achieved by graphite intercalation. It is a bi-intercalation compound with stacking sequence CrCl3NiCl2NiCl2/… where/represents a graphite layer. The two types of chloride layers are much as they occur in the pristine chlorides and have the same lattice parameters and intralayer intertransition–metal ferromagnetic exchange interactions. The transition temperatures for singly intercalated CrCl3 and NiCl2 graphite compounds are, respectively, 11.3, and 20.2 K. The bi-intercalation compound shows a "double transition" with Tc1 and Tc2 being equal to the relevant intercalate-specific temperatures. It is proposed that, as the temperature is lowered, the NiCl2 layers order first at Tc2 into a 3-D antiferromagnetic stacking of ferromagnetic planes, followed by onset of intra-CrCl3-layer ferromagnetic order at Tc1. Below Tc1 the two types of ferromagnetic planes probably assume a 3-D antiferromagnetic stacking that involve both types of layers, requiring that the NiCl2 stacking be different than at Tc1 &lt; T &lt; Tc2. The main interlayer interactions are believed to be dipole–dipole forces and these are seen to give large low-field temperature hysteresis effects. This is in contrast to many layered materials with antiferromagnetic in-plane interactions in which: (i) dipole–dipole forces do not play a significant role, (ii) 3-D order is not intercalate specific but occurs at temperatures that are much lower than the in-plane interaction strengths and that are highly dependent on the interlayer interaction strengths, and (iii) hysteresis effects are not observed.

Electrochemical preparation of the graphite bi-intercalation compound with H 2SO 4 and FeCl 3

Stage- n FeCl 3-GICs ( n = 2,3) prepared in the standard two-zone method were oxidized galvanostatically in H 2SO 4. The electrode potential vs. electric quantity curves observed during the treatment and the X-ray powder patterns of the products showed clearly the intercalation of H 2SO 4 into FeQ 3-GICs and the formation of the graphite bi-intercalation compounds (GBCs) of FeCl 3 and H 2SO 4. The c axis repeat distance I c of the GBCs, 17.38Å, from the stage-2 FeCl 3-GIC was equal to the sum of those of FeCl 3-GIC, 9.38Å, and of H 2SO 4-GIC, 8.00Å. From the stage-3 FeCl 3-GIC the compound with I c of 25.38Å ( = 9.38Å + 8.00Å + 8.00Å), through the intermediate with I c of 20.73Å ( = 9.38Å + 3.35Å + 8.00Å). The electrochemical reduction of these GBCs suggested that the intercalation of H 2SO 4 into FeCl 3-GICs is reversible.

A new biintercalation compound, FeCl3–NiCl2–graphite, studied by 57Fe Mössbauer effect spectroscopy and superconducting quantum interference device magnetization measurements: an ideally decoupled bimagnetic system

A novel situation in which long-range magnetic order coexists with (super)paramagnetism occurs in a new graphite biintercalation compound: FeCl3–NiCl2–graphite. Several compounds have been prepared by sequential intercalation of the two intercalates and have been characterized by powder diffractometry, X-ray precession photographs, high-precision X-ray single-crystal measurements, chemical analysis, and high-temperature susceptibility measurements. All measurements are consistent with the stacking sequence –C–NiCl2–C–FeCl3–C– and corroborate the crystallographic integrity of separate NiCl2 and FeCl3 sublattices. Since the in-plane magnetic interactions of the NiCl2 and FeCl3 layers are, respectively, ferromagnetic and antiferromagnetic, the two types of chloride layers have been probed independently by combining low-temperature superconducting quantum interference device magnetometry and 57Fe Mössbauer-effect spectroscopy. The NiCl2 layers order magnetically at 20.5 K, whereas the FeCl3 layers do not order down to 4.2 K. The drop of 1.5 K in the NiCl2-related ordering temperature, induced by the intercalation of FeCl3 into stage-2 NiCl2–graphite, is attributed to the increased NiCl2–layer separation, suggesting that the transition in NiCl2–graphite is not two-dimensional. Some of the FeCl3–NiCl2–graphite compounds show NiCl2-related transitions at temperatures lower than 20.5 K, which is explained in terms of lower in-plane NiCl2 concentrations. Partial oxidation and hydrolysis of in-gallery FeCl3 has been demonstrated and is found to depend strongly on the mean host-graphite-flake size. A charge transfer of 0.2 electrons per iron atom in the FeCl3 layers is inferred from the Mössbauer spectra collected at 4.2 K, which is the same as in singly intercalated FeCl3–graphite compounds of all known stages. Time and temperature-hysteresis effects in the magnetization have been measured and show distinct "re-entrant spin-glass" behaviour. Relevant aspects of the magnetism and structure of the related singly intercalated materials, the pristine chlorides, and the new biintercalation compounds are compared in detail. The overall features are consistent with a recent model based on interacting island supermoments.