Paramagnetic Ce3 Research Articles

Spin dynamics phenomena of a cerium(III) double-decker complex induced by intramolecular electron transfer.

Switchable spin dynamic properties in single-molecule magnets (SMMs) via an applied stimulus have applications in single-molecule devices. Many SMMs containing heavy lanthanoid ions with strong uniaxial magnetic anisotropy have been reported to exhibit SMM characteristics in the absence of an external magnetic field. On the other hand, SMMs containing light lanthanoid cerium(III) (Ce3+) ions exhibit field-induced slow magnetic relaxation. We investigated the chemical conversion of a diamagnetic Ce4+ ion (4f0) to a paramagnetic Ce3+ ion (4f1) in Ce-phthalocyaninato double-decker complexes (TBA+[Ce(obPc)2]- (1) and TBA+[Ce(Pc)2]- (2)) which exhibit field-induced SMM behaviour due to a 4f1 system. The phthalocyaninato ligands with electron-donating substituents (obPc2- = 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninato) in 1 have a significant effect on the valence state of the Ce ion, which is reflected in its magnetic properties due to the mixed valence state of the Ce ion. Given that Ce double-decker complexes with π-conjugated ligands undergo intramolecular electron transfer (IET) to the Ce ion mixed valence state, characterised by a mixture of 4f0 and 4f1 configurations, we examined the dynamic disorder inherent in IET influencing magnetic relaxation.

Application of EPR Spectroscopy for Investigation of Antisite Defectsin Yttrium-Aluminum Garnet

Paramagnetic Ce3+, Tb3+ and Ho3+ centers in the yttrium position in yttrium aluminum garnet (YAG) crystals investigated by the EPR spectroscopy. Along with the main EPR signals of Ce3+ and non-Kramers Tb3+ ions located in a regular environment a number of new centers with less lines intensity with different g-factors and zero-field splitting observed. The number of lines and the symmetry of these centers indicate that they belong to cerium and terbium ions, near which there are YAl antisite defects (Y3+ in octahedral positions of Al3+) or AlY (Al3+ in dodecahedral positions of Y3+). In addition to the main EPR signals of non-Kramers Ho3+ ions located in Y3+, a number of less intense lines with different parameters also attributed to antisite defects.

The mixed-valence Ce4Al2O10 aluminate

Reversible oxidation-reduction of cerium ions in a monoclinic Ce4Al2O9 aluminate was studied by XRD, TEM, temperature programmed reduction-oxidation and magnetic methods. It has been shown that nanocrystalline Ce4Al2O9 reacts with gaseous oxygen, undergoing at 20–300 °C transformation into a new, oxidized phase described in the same P21/c space group, but with 10% smaller unit cell volume. Magnetic measurements revealed that the oxidized Ce4Al2O9 still contains ~20% of paramagnetic Ce3+ ions. The oxidized Ce aluminate may be reduced back to Ce4Al2O9 by heating in H2 atmosphere to 1000 °C. The reversibility of the oxidation-reduction process of Ce4Al2O9 aluminate bears resemblance to the behaviour of fluorite type CeO2, and may be of interest for applications (e.g., in catalytic high-temperature oxidation reactions).

Low-molecular-weight paramagnetic 19F contrast agents for fluorine magnetic resonance imaging

Objective19F MRI requires biocompatible and non-toxic soluble contrast agents with high fluorine content and with suitable 19F relaxation times. Probes based on a DOTP chelate with 12 magnetically equivalent fluorine atoms (DOTP-tfe) and a lanthanide(III) ion shortening the relaxation times were prepared and tested.MethodsComplexes of DOTP-tfe with trivalent paramagnetic Ce, Dy, Ho, Tm, and Yb ions were synthetized and characterized. 19F relaxation times were determined and compared to those of the La complex and of the empty ligand. In vitro and in vivo 19F MRI was performed at 4.7 T.Results19F relaxation times strongly depended on the chelated lanthanide(III) ion. T1 ranged from 6.5 to 287 ms, T2 from 3.9 to 124.4 ms, and T2* from 1.1 to 3.1 ms. All complexes in combination with optimized sequences provided sufficient signal in vitro under conditions mimicking experiments in vivo (concentrations 1.25 mM, 15-min scanning time). As a proof of concept, two contrast agents were injected into the rat muscle; 19F MRI in vivo confirmed the in vivo applicability of the probe.ConclusionDOTP-based 19F probes showed suitable properties for in vitro and in vivo visualization and biological applications. The lanthanide(III) ions enabled us to shorten the relaxation times and to trim the probes according to the actual needs. Similar to the clinically approved Gd3+ chelates, this customized probe design ensures consistent biochemical properties and similar safety profiles.

Magnetic and thermal properties of ferromagnetic insulator: Yttrium Iron Garnet

We present here the magneto thermal properties, damping behavior and effect of Cerium doping on ferromagnetic insulator Yttrium Iron Garnet (YIG), synthesized via solid state method and Spark Plasma Sintering. The thermal conductivity was measured using Laser Flash technique in the temperature range of 300–1000° K. A decrease in thermal conductivity was observed up to the Curie temperature of YIG, beyond which it showed a constant behavior. On Ce doping of YIG, 15% enhancement of thermal conductivity was achieved, besides leading to an increase of magnetic moment at all temperatures. This gain is attributed to the increase of grain size and replacement of diamagnetic Y3+ ions in YIG by paramagnetic Ce3+ ions in Ce doped YIG. The spark plasma sintered YIG showed a decrease in particle size and grain size resulting in decrease of both thermal conductivity and saturation magnetization. The damping parameters obtained from ferromagnetic resonance measurement revealed a very low magnetic damping even on Ce doping. The work provides effective information regarding the enhancement of spin dynamic properties of YIG suitable for spin-caloritronic applications.

STUDY OF PARTIALLY STABILIZED CE DOPED ZRO2 CRYSTALS BY ELECTRON PARAMAGNETIC RESONANCE

The study of crystals of ZrO2 solid solutions (PSZ) stabilized with yttrium and cerium oxides was carried out by electron paramagnetic resonance (EPR) in the X and Q range. The presence of Zr3+ centers in annealed ZrO2 crystals stabilized only by yttrium oxide (2.8 mol.% Y2O3) is established. Another kind of paramagnetic O−centers appear when CeO2 is added to ZrO2 crystals in addition to yttrium oxide. To estimate the concentration of Ce3+ ions in PZS crystals, EPR spectra were recorded in the presence of a reference specimen at 7 K. Paramagnetic Ce3+ ions have been identified and their relative amounts in PSZ crystals before and after high−temperature heat treatment has been measured. The annealing in air leads to a decrease in the concentration of Ce3+ ions for all compositions and changes the color of the crystals from red to white. After annealing in the 2.0Y0.8Ce3Zr sample, the amount of paramagnetic Ce3+ ions decreased approximately twice. Paramagnetic centers from Ce3+ are not detected in a the sample with a low cerium content of 0.1 mol.% after annealing which indicates the complete transition of Ce3+ to the Ce4+ state. It is shown that the formed paramagnetic centers of cerium are bound by strong exchange interactions. No angular dependence of the EPR lines for the paramagnetic Ce3+ cations on the applied external magnetic field was observed. The probable reason for the absence of such angular dependence is that impurity rare−earth ions are located next to each other, forming impurity clusters with effective spin Seff = 1/2.

Binary Ce(III) and Li(I) triflate salt composition for solid polymer electrolytes

This study describes the results of the characterization of solid polymer electrolytes using chitosan matrix plasticized with glycerol and doped with cerium and lithium triflate binary salt composition. The electrolytes were prepared by solvent casting method and characterized by thermal analysis (thermogravimetric analysis—TGA and differential scanning calorimetry—DSC), impedance measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and electron paramagnetic resonance (EPR). Samples are thermally stable up to 128–153 °C, and most of them are amorphous. In some cases, the appearance of crystalline peaks is due to the diffraction of salt domains, which makes the samples less conductive. The room temperature conductivity maximum of 10−6 S cm−1 at 30 °C was obtained for the samples with the same total salt mass of 0.15 g (ChitCeTrif0.05LiTrif0.10 and ChitCeTrif0.10LiTrif0.05). Finally, the EPR analysis suggests that the local coordination environment of the paramagnetic Ce3+ is not the same in different samples. In summary, beside the modest conductivity values of these samples, they are still adequate for some electrochemical applications.

Competition between Superconductivity and Magnetism in Non-centrosymmetric (La1−xCex)NiC2

The superconducting and magnetic properties of non-centrosymmetric (La1−xCex)NiC2 solid solutions have been studied by X-ray diffraction, electrical resistivity, specific heat and magnetic measurements. The paramagnetic susceptibility shows that Ce forms localized magnetic moments of about 2.5 μB, the value expected for a Ce3+ free ion, throughout the whole concentration range. With these localized magnetic moments, the superconducting transition temperature Tc of ∼2.8 K for LaNiC2 decreases rapidly, disappearing at about 2 at. % Ce. This marked suppression of Tc by the paramagnetic Ce impurities implies that the system is a BCS-type superconductor with a full energy gap. The substitution of La for Ce also substantially changes the unique magnetism of CeNiC2 that exhibits successive transitions from the paramagnetic state to an incommensurate antiferromagnetic ordering below 20 K, then to a commensurate antiferromagnetic state at 10 K, and further to a ferromagnetic (or ferrimagnetic) order below 2 K. By ...

Electron paramagnetic resonance study of Ce doped partially stabilized ZrO2 crystals

ZrO2 (PSZ) solid solutions crystals stabilized with yttrium and cerium oxides have been studied using electron paramagnetic resonance (EPR) in the X and Q ranges. Zr3+ have been observed centers in the as-annealed ZrO2 crystals stabilized only by yttrium oxide (2.8mol% Y2O3). Another type of paramagnetic-O-centers appear as a result of CeO2 addition to ZrO2 crystals along with yttrium oxide. To estimate the concentration of Ce3+ ions in PZS crystals, we recorded the EPR spectra in the presence of a reference at 7K. Paramagnetic Ce3+ ions have been identified and their relative amount in the PSZ crystals before and after high-temperature heat treatment has been assessed. Annealing in air leads decreases the concentration of Ce3+ ions for all the test compositions and changes the color of the crystals from red to white. After annealing of the sample 2.0Y0.8Ce3Zr, the amount of paramagnetic Ce3+ ions decreased approximately twofold. Paramagnetic centers from Ce3+ have not been detected in the specimen with a low cerium content of 0.1mol% after annealing which indicates the complete transition of Ce3+ to the Ce4+ state. We show that the forming cerium paramagnetic centers are bound by strong exchange interactions. No angular dependence of the EPR lines of the paramagnetic Ce3+ cations on the applied external magnetic field has been observed. Probable origin of the absence of angular dependence is that the impurity rare-earth ions are located close to one another, forming impurity clusters with an effective spin of Seff=1/2.

Different metamagnetism between paramagnetic Ce and Yb isomorphs

To solve the puzzle of metamagnetic phenomena in heavy fermion systems, we have compared paramagnetic isostructural Ce and Yb systems, CeNi$_2$Ge$_2$ and YbNi$_2$Ge$_2$, both of which are located near a magnetic instability. The most intriguing result is discovery of a metamagnetic-like transition in both systems from magnetization measurements in a pulsed magnetic fields. This is the first observation of the metamagnetism for isomorphic Ce and Yb paramagnetic systems. Similar to other metamagnets, the metamagnetic transition fields for both compounds are well scaled by the temperature $T_{\chi}^{\rm max}$, at which the magnetic susceptibility shows a maximum. In addition, for CeNi$_2$Ge$_2$ a peak of nonlinear susceptibility $\chi_3$ appears at approximately $T_{\chi}^{\rm max}/2$, as for other heavy-fermion metamagnets. In contrast, YbNi$_2$Ge$_2$ shows only a sign change for $\chi_3$ at $T_{\chi}^{\rm max}$, as observed in itinerant metamagnets located near the ferromagnetic critical point. The metamagnetism of CeNi$_2$Ge$_2$ corresponds to a typical Kondo lattice system, whereas that of YbNi$_2$Ge$_2$ is similar to the nearly ferromagnetic itinerant systems. Other possibilities for the metamagnetic behavior of YbNi$_2$Ge$_2$ are also discussed.

Structural elucidation, EPR and photoluminescent property of a Ce(III) two dimensional coordination polymer with 4,4′-bipyridine and 2-sulfoterephthalate

A new Ce(III) coordination polymer, {[Ce(stp)(bipy)(H2O)]·H2O}n (1) is afforded via the reaction of trivalent cerium nitrate [Ce(NO3)3·6H2O], 2-sulfoterephthalic acid monosodium salt Na(H2stp), and 4,4′-bipyridine (bipy). Based upon the versatile coordination modes of the stp ligand as linker and bipy as connector, the aforementioned compound is arranged in a 2-D network, as evidenced by single-crystal X-ray diffraction technique. In 1, the central Ce atom possesses on a distorted tricapped trigonal-prismatic coordination environment. The EPR measurement reveals that there exhibits a weak antiferromagnetic coupling between paramagnetic Ce3+ ions. The encapsulation of the Ce(III) CP disposes a moderate luminescent activity. Thermal analysis is also carried out to check the water loss of the molecule which is in accordance with the structural evidence.

Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-xSex (x = 0.5 and 1.0), a non-U material with Tc < TFM.

We have carried out detailed magnetic and transport studies of the new Sr0.5Ce0.5FBiS2-xSex (0.0 ≤ x ≤ 1.0) superconductors derived by doping Se in Sr0.5Ce0.5FBiS2. Se–doping produces several effects: it suppresses semiconducting–like behavior observed in the undoped Sr0.5Ce0.5FBiS2, the ferromagnetic ordering temperature, TFM, decreases considerably from 7.5 K (in Sr0.5Ce0.5FBiS2) to 3.5 K and the superconducting transition temperature, Tc, gets enhanced slightly to 2.9–3.3 K. Thus in these Se–doped materials, TFM is marginally higher than Tc. Magnetization studies provide evidence of bulk superconductivity in Sr0.5Ce0.5FBiS2-xSex at x ≥ 0.5 in contrast to the undoped Sr0.5Ce0.5FBiS2 (x = 0) where magnetization measurements indicate a small superconducting volume fraction. Quite remarkably, as compared with the effective paramagnetic Ce–moment (~2.2 μB), the ferromagnetically ordered Ce–moment in the superconducting state is rather small (~0.1 μB) suggesting itinerant ferromagnetism. To the best of our knowledge, Sr0.5Ce0.5FBiS2-x Sex (x = 0.5 and 1.0) are distinctive Ce–based bulk superconducting itinerant ferromagnetic materials with Tc < TFM. Furthermore, a novel feature of these materials is that they exhibit a dual and quite unusual hysteresis loop corresponding to both the ferromagnetism and the coexisting bulk superconductivity.

EPR of Се3+ in the Rb2NaYF6 single crystal

The EPR spectrum of the Ce3+ ion in the crystal of the elpasolite type Rb2NaYF6 has been observed and studied at low temperatures (Т = 4.2 – 80 K). It was established that the paramagnetic center Ce3+ has tetragonal symmetry confirming the experimental fact we reported recently that at low temperatures the Rb2NaYF6 crystal exists in the tetragonal phase, into which it transferred from the cubic phase as a result of the structural phase transition (PT). Parameters of the spin Hamiltonian of the tetragonal EPR spectrum were determined. A scheme of 4f energy levels of the Ce3+ ion in Rb2NaYF6 before and after PT was proposed from the theoretical interpretation of the observed g-factors and parameters of the crystal fields acting on it were determined.

Investigation of the hydrothermal crystallisation of the perovskite solid solution NaCe1−La Ti2O6 and its defect chemistry

Perovskites of nominal composition NaCe1−xLaxTi2O6 (0≤x≤1) crystallise directly under hydrothermal conditions at 240 °C. Raman spectroscopy shows distortion from the ideal cubic structure and Rietveld analysis of powder X-ray and neutron diffraction reveals that the materials represent a continuous series in rhombohedral space group R3c. Ce LIII-edge X-ray absorption near edge structure spectroscopy shows that while the majority of cerium is present as Ce3+ there is evidence for Ce4+. The paramagnetic Ce3+ affects the chemical shift and line width of 23Na MAS NMR spectra, which also show with no evidence for A-site ordering. 2H MAS NMR of samples prepared in D2O shows the inclusion of deuterium, which IR spectroscopy shows is most likely to be as D2O. The deuterium content is highest for the cerium-rich materials, consistent with oxidation of some cerium to Ce4+ to provide charge balance of A-site water.

First-order spin reorientation transition and specific-heat anomaly in CeFeO3

We report the successful synthesis of single-phase polycrystalline CeFeO3, and a thorough study of its magnetic and thermal properties. An abrupt spin reorientation transition occurs at T = 240 K, indicating a first-order phase transition from Γ4 (Gx, Ay, Fz) to Γ1 (Ax, Gy, Cz). A distinct thermal anomaly in the specific heat due to spin reorientation has been detected, with the onset and completion of the spin reorientation at 240 K and 220 K, respectively. The low-temperature specific heat exhibits a Schottky anomaly caused by paramagnetic Ce3+. The very-low-temperature specific heat increases with increasing the applied magnetic field, suggesting an antiferromagnetic transition of Ce3+ exists below T = 1.8 K.

Review on cerium intermetallic compounds: A bird's eye outlook through DFT

Cerium based intermetallic compounds exhibit a wealth of physical properties originating from the electronic states of Ce, i.e. diamagnetic Ce4+ ([Xe] 4f0), paramagnetic Ce3+ ([Xe] 4f1). Switching between the electronic states can be induced either chemically such as by inserting hydrogen, by substitutions (size effects) or physically by applying external pressure. The review exposes different classes of Ce intermetallic compounds whose properties are interpreted and/or predicted thanks to quantum computations in the framework of the density functional theoretical (DFT). Focus is broadly made on the family of the equiatomic cerium intermetallic compounds, namely ternary CeTX where T is a transition metal and X a p-element where the hydrogenation effects take a considerable place in changing the electronic configuration of Ce. Other stoichiometries of cerium intermetallic compounds with their physical properties are discussed subsequently in the later part of the review. Rather than presenting an exhaustive enumeration of stoichiometries, illustrative case studies are selected for each class of materials to provide, after presenting the experimental context, insights into original outcome from methods targeted at selective physical and chemical properties.

Doped Semimetal Clusters: Ternary, Intermetalloid Anions [Ln@Sn7Bi7]4– and [Ln@Sn4Bi9]4– (Ln = La, Ce) with Adjustable Magnetic Properties

Two K([2.2.2]crypt) salts of lanthanide-doped semimetal clusters were prepared, both of which contain at the same time two types of ternary intermetalloid anions, [Ln@Sn(7)Bi(7)](4-) and [Ln@Sn(4)Bi(9)](4-), in 0.70:0.30 (Ln = La) or 0.39:0.61 (Ln = Ce) ratios. The cluster shells represent nondeltahedral, fullerane-type arrangements of 14 or 13 main group metal atoms that embed the Ln(3+) cations. The assignment of formal +III oxidation states for the Ln sites was confirmed by means of magnetic measurements that reveal a diamagnetic La(III) compound and a paramagnetic Ce(III) analogue. Whereas the cluster anions with a 14-atomic main-group metal cage represent the second examples in addition to a related Eu(II) cluster published just recently, the 13-atomic cages exhibit a yet unprecedented enneahedral topology. In contrast to the larger cages, which accord to the Zintl-Klemm-Busmann electron number-structure correlation, the smaller clusters require a more profound interpretation of the bonding situation. Quantum chemical investigations served to shed light on these unusual complexes and showed significant narrowing of the HOMO-LUMO gap upon incorporation of Ce(3+) within the semimetal cages.

The effect of ring size variation on the structure and stability of lanthanide(iii) complexes with crown ethers containing picolinate pendants

The coordination properties of the macrocyclic receptor N,N'-bis[(6-carboxy-2-pyridyl)methylene]-1,10-diaza-15-crown-5 (H(2)bp15c5) towards the lanthanide ions are reported. Thermodynamic stability constants were determined by pH-potentiometric titration at 25 °C in 0.1 M KCl. A smooth decrease in complex stability is observed upon decreasing the ionic radius of the Ln(III) ion from La [log K(LaL) = 12.52(2)] to Lu [log K(LuL) = 10.03(6)]. Luminescence lifetime measurements recorded on solutions of the Eu(III) and Tb(III) complexes confirm the absence of inner-sphere water molecules in these complexes. (1)H and (13)C NMR spectra of the complexes formed with the diamagnetic La(III) metal ion were obtained in D(2)O solution and assigned with the aid of HSQC and HMBC 2D heteronuclear experiments, as well as standard 2D homonuclear COSY and NOESY spectra. The (1)H NMR spectra of the paramagnetic Ce(III), Eu(III) and Yb(III) complex suggest nonadentate binding of the ligand to the metal ion. The syn conformation of the ligand in [Ln(bp15c5)](+) complexes implies the occurrence of two helicities, one associated with the layout of the picolinate pendant arms (absolute configuration Δ or Λ), and the other to the five five-membered chelate rings formed by the binding of the crown moiety (absolute configuration δ or λ). A detailed conformational analysis performed with the aid of DFT calculations (B3LYP model) indicates that the complexes adopt a Λ(λδ)(δδλ) [or Δ(δλ)(λλδ)] conformation in aqueous solution. Our calculations show that the interaction between the Ln(III) ion and several donor atoms of the crown moiety is weakened as the ionic radius of the metal ion decreases, in line with the decrease of complex stability observed on proceeding to the right across the lanthanide series.

Ordering mechanism and spin fluctuations in a geometrically frustrated heavy-fermion antiferromagnet on the Kagome-like lattice CePdAl: AAl27NMR study

$^{27}\mathrm{Al}$ NMR measurements have been performed to investigate the ordering mechanism and spin fluctuations in a geometrically frustrated heavy-fermion antiferromagnet on the Kagome-like lattice CePdAl. This compound shows a partially ordered state below ${T}_{\mathrm{N}}$ $(2.7\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, in which $1∕3$ of the Ce moments remain paramagnetic. Whether the remaining paramagnetic moments order at lower temperature or not has been controversial. Our NMR measurements show that the nuclear magnetic relaxation rate ${T\phantom{\rule{0.2em}{0ex}}}_{1}^{\ensuremath{-}1}$ is proportional to the temperature below $0.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and there is no other phase transition down to $30\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. The simulation of the spin echo spectra shows that the observed spectra are compatible with the partially ordered state and an incommensurate $k$ vector along the $c$ axis down to the lowest temperature. These results demonstrate that the paramagnetic Ce moments in the partially ordered state are in a heavy-fermion state and consequently the partially ordered state is considered to be stable down to $0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature dependence of ${T\phantom{\rule{0.2em}{0ex}}}_{1}^{\ensuremath{-}1}$ also shows that antiferromagnetic correlations develop from much higher temperatures above ${T}_{\mathrm{N}}$.

Study of structural evolution in Ce‐ and Nd‐doped aluminoborosilicate glasses under β‐irradiation

AbstractThe structural changes in aluminoborosilicate glasses under β‐irradiation as a function of rare earth oxide content and the dose have been studied using Electron Paramagnetic Resonance (EPR) and luminescence spectroscopies. The EPR measurements at helium temperature (4 K) showed that β‐irradiation affects valence state of cerium ions. According to concentration and dose dependences, the line with g ∼ 2.89 can be attributed to paramagnetic Ce3+ ions resulting from Ce4+ reduction under irradiation. The effect of CeO2 content leads to the modifications of the EPR signal of defects at helium and the change in the relative proportion of electron and hole defects with the increase of the cerium doping level at room temperature. We observed also a decrease of the defect concentration as a function of the Nd doping into these glass compositions but by two orders less than for Ce‐doped samples. Exposure to irradiation induced the appearance of a non‐resolved EPR band in the region of defects. We can assume that possible dipolar interaction between Nd3+ ion and hole can result in not typical EPR resonance shape of paramagnetic defects at g ∼ 2. Moreover, estimation of the ratio between splitted components of the 4F3/2 – 4I9/2 transition depending on the irradiation dose showed that dose increase leads to increase of this ratio suggesting that the nearest environment of Nd ions is expected to be changed. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)