Unpaired 4f Electrons Research Articles

Rare earth Ce-doped W-type barium ferrites for tunable electromagnetic waves absorption performance

W-type ferrites possessing low cost and high chemical stability, show high potential in electromagnetic wave (EMW) absorption field. However, due to the low dielectric loss, developing high EMW absorption performance of W-type ferrites remains desired. Here, rare earth (RE) cerium (Ce)-doped W-type barium ferrites (Ba1-yCeyNi2Fe15.4O27, y = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) are prepared by a sol-gel approach. The influences of Ce doping are detailed analyzed. Ce ions with unpaired 4f electrons and strong spin-orbit coupling of angular momentum enhance the dielectric and magnetic properties of ferrites. Ba0.7Ce0.3Ni2Fe15.4O27 achieves the minimum reflection loss (RLmin) value of -52 dB while Ba0.6Ce0.4Ni2Fe15.4O27 showcases the widest effective absorption bandwidth (EAB) of 1.36 GHz associated with the RLmin reaching -38 dB, significantly outperforming the undoped ferrites. This work thus demonstrates a high-efficiency utilization of Ce for enhancing the EMW absorption performance of widely employed W-type barium ferrites, efficiently advancing the application field of RE elements.

Electronic states of the constituent magnetic elements, superior magnetic properties and spin-flip metamagnetic transition in Cu3Dy(SeO3)2O2Cl

Dy based cuprate francisite [Cu3Dy(SeO3)2O2Cl, in short DyCufr] is so far potentially the most fascinating magnetic compound in the class of francisite compounds. Synthesized DyCufr has been investigated via structural, X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and magnetization measurements. XANES and XPS provide consistent and corroborative results regarding electronic states of the constituent elements. The most striking observation is that the slope of magnetization for the field induced metamagnetic transition (MMT) attains nearly infinity (perfect), hysteresis associated with MMT is substantially high, and the critical field for MMT is very low. The antiferromagnetic ordering temperature (TN), saturation magnetization (MS) are very high, and the remanent magnetization (MR) is appreciable in DyCufr in contrast to few other similar compounds. Unpaired 4f electrons of Dy3+ causing high value of effective magnetic moment and spin-flip type metamagnetism are pivotal for producing magnetically the most superior francisite. Actually, sharp MMT as evidenced in DyCufr, has the potential to be used in magneto-refrigeration and spin-electronic devices because it can produce an avalanche flip of spin structure from low-spin (antiferromagnetic) to high-spin (ferromagnetic) state.

Competing Magnetic Interactions and the Role of Unpaired 4f Electrons in Oxygen-Deficient Perovskites Ba3RFe2O7.5 (R = Y, Dy)

Oxygen-deficient perovskite compounds with the general formula Ba3RFe2O7.5 present a good opportunity to study competing magnetic interactions between Fe3+ 3d cations with and without the involvement of unpaired 4f electrons on R3+ cations. From analysis of neutron powder diffraction data, complemented by ab initio density functional theory calculations, we determined the magnetic ground states when R3+ = Y3+ (non-magnetic) and Dy3+ (4f9). They both adopt complex long-range ordered antiferromagnetic structures below TN = 6.6 and 14.5 K, respectively, with the same magnetic space group Ca2/c (BNS #15.91). However, the dominant influence of f-electron magnetism is clear in temperature dependence and differences between the size of the ordered moments on the two crystallographically independent Fe sites, one of which is enhanced by R-O-Fe superexchange in the Dy compound, while the other is frustrated by it. The Dy compound also shows evidence for temperature- and field-dependent transitions with hysteresis, indicating a field-induced ferromagnetic component below TN.

Enhancement of magnetic properties of Sm-Co nano composite ribbons by heavy lanthanide doping

Sm-Co magnets becoming more and more interesting among research community since 1950′s due to its essential role in space and transport industry to be used in some precious instruments such as, sensors, actuators, motors, and gyroscope. The combination of Rare-earth (RE) and Transition metal (TM) is an ideal combination to make a high-performance magnet, as the RE provides the high magneto crystalline anisotropy (HA) and the TM provides the high magnetization (Ms) and high Curie temperature (Tc). SmCo5 compound possesses Tc as high as ∼ 700 °C. Previous studies have reported that HRE (Gd, Dy, Er and Ho) could be used as a temperature compensation material as unpaired 4f electrons in shell gives rise to maximum magnetic moment. In this study, effect of lanthanides (HREs - Gd and/ Dy) on microstructure and magnetic properties of Sm-Co-based rapidly solidified alloy ribbons have been reported. Phase analyses confirmed the presence of 1:5H phase which was prevalent along with a fraction of 2:17R phase in all the alloy ribbons. Hc value was increased from 10.9 to 13.3 kOe (1.09 to 13.3 T) and Br value was increased from 12.5 to 16.2 kG (1.25 to 1.62 T) with Dysprosium addition.

Structural, Optical, and Magnetic Properties of Erbium-Substituted Yttrium Iron Garnets.

We synthesized a series of slightly erbium-substituted yttrium iron garnets (Er:YIG), Y3–xErxFe5O12 at different Er concentrations (x = 0, 0.01, 0.05, 0.10, and 0.20) using a solid-state reaction and investigated their structural, magnetic, and optical properties as a function of Er concentration. The volume of the unit cell slightly increased with Er concentration and Er atoms predominately replaced Y atoms in the dodecahedrons of YIG. The optical properties exhibited certain decreases in reflectance in the 1500–1600 nm wavelength range due to the presence of Er3+. Despite the many unpaired 4f electrons in Er3+, the total magnetic moments of Er:YIG showed similar trends with temperatures and magnetic fields above 30 K. An X-ray magnetic circular dichroism study confirmed the robust Fe 3d magnetic moments. However, the magnetic moments suddenly decreased to below 30 K with Er substitution, and the residual magnetism (MR) and coercive field (HC) in the magnetic hysteresis loops decreased to below 30 K with Er substitution. This implies that Er substitution in YIG has a negligible effect on magnetic properties over a wide temperature range except below 30 K where the Er 4f spins are coupled antiparallel to the majority Fe 3d spins. Our studies demonstrated that above 30 K the magnetic properties of YIG are retained even with Er substitution, which is evidence that the Er doping scheme is applicable for YIG-based magneto-optical devices in the mid-infrared regime.

Two new rare-earth orthoborates Ba2CdLn2(BO3)4 (Ln = Tb, Eu) and multicolor tunable emission in the Ba2CdTb2-2xEu2x(BO3)4 (0 ≤ x ≤ 0.2) phosphors

Two new rare-earth orthoborates Ba2CdLn2(BO3)4 (Ln = Tb, Eu) were prepared by the high-temperature solution reactions at 950 °C. The single-crystal XRD analyses showed that they crystallized in the monoclinic space group P21/c and the crystal structures consisted of 3D networks constructed by CdO5 square pyramids (CdO6 mono-capped square pyramids), Tb(Eu)On (n = 7, 8) polyhedra and BO3 planar triangles, with open channels accommodating Ba2+ cations. The IR and Raman studies supported the presence of BO3 groups in the structures and the UV–vis absorption measurements showed the typical Tb3+ and Eu3+ absorption bands arising from their unpaired 4f electrons. In addition, solid solutions Ba2CdTb2-2xEu2x(BO3)4 (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction method. By doping Eu3+ into the Ba2CdTb2(BO3)4 host and varying the doping concentration of Eu3+, tunable colors from green to orange and eventually to red were obtained in the Ba2CdTb2-2xEu2x(BO3)4 phosphors under the excitation at 377 nm. The energy transfer process from Tb3+ to Eu3+ was verified through luminescence spectra and fluorescence decay curves. The above results indicated that the Ba2CdTb2-2xEu2x(BO3)4 phosphors may find potential applications in the field of displays and lighting.

CeTiO2N oxynitride perovskite: paramagnetic 14N MAS NMR without paramagnetic shifts

Abstract 14N magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of diamagnetic LaTiO2N perovskite oxynitride and its paramagnetic counterpart CeTiO2N are presented. The latter, to the best of our knowledge, constitutes the first high-resolution 14N MAS NMR spectrum collected from a paramagnetic solid material. The unpaired 4f-electrons in CeTiO2N do not induce a paramagnetic 14N NMR shift. This is remarkable given the direct Ce−N contacts in the structure for which ab initio calculations predict substantial Ce→14N contact shift interaction. The same effect is revealed with 14N MAS NMR for SrWO2N (unpaired 5d-electrons).

Syntheses, structure determination and characterization of two novel non-centrosymmetric mixed alkali rare-earth orthoborates: K3Li3RE7(BO3)9 (RE=Dy, Tb)

Single crystals of novel mixed alkali rare-earth orthoborates K3Li3Dy7(BO3)9 and K3Li3Tb7(BO3)9 were obtained by spontaneous crystallization from high temperature flux. The structure determination from single crystal X-ray diffraction relevels that K3Li3Dy7(BO3)9 and K3Li3Tb7(BO3)9 crystallize into the non-centrosymmetric orthorhombic space group Pca21 with the lattice parameters of a = 20.8225(5) Å, b = 6.4118(2) Å, c = 17.4976(4) Å, Z = 4 and a = 20.9218(9) Å, b = 6.4420(3) Å, 17.5285(8) Å, Z = 4, respectively. Their condensed three-dimensional networks feature infinite triangle-wave chains composed of [RE5O32] polyhedral pentamers, which are further connected by RE2O14 dimmer and isolated BO3 planar groups. K+ and Li+ cations are situated in interstitial voids in-between these chains. The UV–Vis diffuse spectra of K3Li3Dy7(BO3)9 and K3Li3Tb7(BO3)9 show the typical Dy3+ and Tb3+ absorption bands arising from their unpaired 4f electrons. Large bandgaps of these two rare-earth borates for both direct and indirect optical transition were determined using Tauc plots. Excited by the ultraviolet light, K3Li3Dy7(BO3)9 and K3Li3Tb7(BO3)9 were observed to emit the strong bule and green luminescence, respectively. In addition, polycrystalline of Ho-, Er- and Sm-analogues were synthesized via solid-state reaction. The lattice parameters of whole members, determined by Rietveld refinement, are found to obey the lanthanide contraction.

Observation of highly stable and symmetric lanthanide octa-boron inverse sandwich complexes

While boron forms a wide range of metal borides with important industrial applications, there has been relatively little attention devoted to lanthanide boride clusters. Here we report a joint photoelectron spectroscopy and quantum chemical study on two octa-boron di-lanthanide clusters, Ln2B8- (Ln = La, Pr). We found that these clusters form highly stable inverse sandwich structures, [Ln-B8-Ln]-, with strong Ln and B8 bonding via interactions between the Ln 5d orbitals and the delocalized σ and π orbitals on the B8 ring. A (d-p)δ bond, involving the 5dδ and the antibonding π orbital of the B8 ring, is observed to be important in the Ln-B8 interactions. The highly symmetric inverse sandwich structures are overwhelmingly more stable than any other isomers. Upon electron detachment, the (d-p)δ orbitals become half-filled, giving rise to a triplet ground state for neutral La2B8 In addition to the two unpaired electrons in the (d-p)δ orbitals upon electron detachment, the neutral Pr2B8 complex also contains two unpaired 4f electrons on each Pr center. The six unpaired spins in Pr2B8 are ferromagnetically coupled to give rise to a septuplet ground state. The current work suggests that highly magnetic Ln…B8…Ln inverse sandwiches or 1D Ln…B8…Ln nanowires may be designed with novel electronic and magnetic properties.

First-principles study on electronic and magnetic and optical properties of rare-earth metals (RE = La, Ce, Nd) doped phosphorene

ABSTRACTThe electronic and magnetic and optical properties of rare-earth metals (RE = La, Ce, Nd) doped phosphorene were investigated by first-principles calculations. The results show that all the structures of RE-doped systems are stable and the magnetic moments of 1.00 μB and 3.45 μB are separately induced in the Ce-doped and Nd-doped systems, which can be used as potential spin polarized dilute semiconductors. The unpaired 4f electrons of Ce and Nd atoms provide the main contribution to induce the magnetic moments. The RE atoms doping result in a blue shift of the absorption peaks and enhance the absorption ability of optical intensity in the visible and infrared region. These results can provide references for improving the physical properties of two-dimensional phosphorene, which are valuable for its potential applications in spintronic and optoelectronic devices.

Probing influence of rare earth ions (Er3+, Dy3+ and Gd3+) on structural, magnetic and optical properties of magnetite nanoparticles

Fe3−xRExO4 (RE = Er, Dy and Gd) nanoparticles with x varying from 0 to 0.1 were synthesized using co-precipitation method. The synthesized nanoparticles were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and UV-Vis spectroscopy techniques. TEM images reveal round shaped particles of ∼8–14 nm diameter in case of undoped magnetite (Fe3O4) nanoparticles whereas there is evolution of rod like structures by the doping of RE ions with aspect ratio in the range of 6–16. The room temperature saturation magnetization (Ms) values show gradual increase with doping till a critical doping level which is found to depend on the ionic radius of dopant ion (x = 0.01 for Er, 0.03 for Dy and 0.04 for Gd). There is a variation in the maximum value of saturation magnetization which is directly proportional to the number of unpaired 4f electrons in the dopant element. Low temperature magnetization study, carried out at 5 K and 120 K reveal an increase in the value of Ms as well as coercivity. The direct bandgaps calculated from UV-Visible data are found to decrease with increasing number of unpaired electrons in the dopant ions.

Structural and Magnetic Properties of $$\hbox {Eu}^{3+}$$ Eu 3 + -Doped $$\hbox {CdNb}_{2}\hbox {O}_{6}$$ CdNb 2 O 6 Powders

Europium-doped $$\hbox {CdNb}_{2}\hbox {O}_{6}$$ powders with the molar concentration of $$\hbox {Eu}^{3+}$$ (0.5, 3 and 6 mol%) were successfully prepared at $$900\,^{\circ }\hbox {C}$$ by using molten salt synthesis method. The effect of europium (Eu) molar concentration on the structural and temperature-dependent magnetic properties of $$\hbox {CdNb}_{2}\hbox {O}_{6}$$ powders has been investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) techniques in the temperature range of 10–300 K. XRD results confirm that all the powders have orthorhombic crystal structure. It has been confirmed from VSM and FMR measurements that $$\hbox {Eu}^{3+}$$ -doped $$\hbox {CdNb}_{2}\hbox {O}_{6}$$ powders have ferromagnetic behaviour for each $$\hbox {Eu}^{3+}$$ molar concentration between 10 and 300 K. XRD and EDX analyses indicate that there is no magnetic impurity in $$\hbox {Eu}^{3+}$$ -doped $$\mathrm{CdNb}_2\mathrm{O}_6$$ powders, supporting that the ferromagnetic behaviour of the powders arises from $$\hbox {Eu}^{3+}$$ ions. The observed ferromagnetism was elucidated with the intrinsic exchange interactions between the magnetic moments associated with the unpaired 4f electrons in $$\hbox {Eu}^{3+}$$ ions. The saturation magnetization decreases with increasing $$\hbox {Eu}^{3+}$$ molar concentration. The temperature-dependent magnetization behaviour was observed not to agree with Curie–Weiss law because europium obeys Van Vleck paramagnetism. Broad FMR spectra and a g-value higher than 2 were observed from FMR measurements, indicating the ferromagnetic behaviour of the powders. It was found that while the resonance field of FMR spectra decreases, the linewidth increases as a function of $$\hbox {Eu}^{3+}$$ molar concentration.

Ultrasmall Gd2O3 nanoparticles surface-coated by polyacrylic acid (PAA) and their PAA-size dependent relaxometric properties

Ultrasmall Gd2O3 nanoparticles can potentially be used as a positive magnetic resonance imaging (MRI) contrast agent owing to their high content of Gd(III), which exhibits the highest spin magnetic moment of all elements due to its seven unpaired 4f electrons. Herein, the above nanoparticles (average diameter = 2.0 nm) were coated with hydrophilic biocompatible polyacrylic acids (PAAs) of different molecular weights (Mw = 1200, 5100, 15000 Da), and the PAA-size-dependent relaxometric properties of the thus obtained composites were investigated. In addition, the biocompatibility of these composites was assessed by in-vitro cell viability measurements. Finally, dose-dependent R1 map images were acquired, proving that PAA-coated nanoparticles can be used as a T1 MRI contrast agent.

First principle investigations of the Pbnm phase BiFeO3, BiFe0.875Mn0.125O3 and Bi0.875X0.125Fe0.875Mn0.125O3 (XBFM) (X = Ce, Gd, Lu)

The structural, magnetic, electronic and optical properties of Pbnm BiFeO[Formula: see text] (BFO), BiFe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (BFM), Bi[Formula: see text]X[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (XBFM) (X = Ce, Gd, Lu) have been investigated by the first principles within the PBE[Formula: see text]+[Formula: see text]U scheme. It is shown that the dopant Mn in the B sites and Ce (Gd, Lu) in the A sites improves the crystalline quality. The magnetic moments of Bi[Formula: see text]Ce[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (CBFM) and Bi[Formula: see text]Gd[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (GBFM) are 10 [Formula: see text] and 16 [Formula: see text] which mainly arises from the strongly localized unpaired 4f electrons of Ce and Gd, 3d electrons of Mn and Fe. While, as BFM, the magnetic moment of Bi[Formula: see text]Lu[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (LBFM) is 9 [Formula: see text] indicating no effect on the magnetization is made by Lu for its full 4f states. The densities of states of the five systems hint that CBFM is metallic and BFM, GBFM, LBFM are still semiconductors. The metallic properties of CBFM arise from the hybridization between Ce-4f and Mn-3d states which leads the Mn [Formula: see text] states to be split into [Formula: see text] and [Formula: see text] lowering the bottom of the conduction band to cross the Fermi level. Furthermore, we also study the optical properties of Pbnm BiFeO[Formula: see text] (BFO), BiFe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (BFM), Bi[Formula: see text]X[Formula: see text]Fe[Formula: see text]Mn[Formula: see text]O[Formula: see text] (XBFM) (X = Ce, Gd, Lu). In this work, the optical properties including the absorption spectrum, loss function, refractive index and reflectivity spectrum are discussed in detail.

Achieving room temperature ferromagnetism in ZnO nanoparticles via Dy doping

The tunable room-temperature ferromagnetism (RTFM) of ZnO nanoparticles through Dy doping were fabricated through a simple co-precipitation method for spintronic device applications. The synthesized samples were analyzed by studying their structural, morphological, optical, chemical, and magnetic properties. X-ray diffraction, selected area electron diffraction, and X-ray photoelectron spectroscopy results display that the Dy3+ have successfully entered for a few of the Zn2+ as a substitute in the ZnO crystal lattice without altering their hexagonal structure. Morphology studies of the suspensions consist of monodisperse and slightly hexagonal shaped nanoparticles. The tunable optical band gap was observed in the ZnO samples via Dy doping, confirmed by diffuse reflectance spectroscopy studies. Declaration of RTFM of the ZnO:Dy has been established with the noticed hysteresis in M–H loops and these studies indicate that the saturation magnetization of the ZnO sample as a function of Dy content. Amalgamating with the above results, it is suggested that, the observed RTFM in the ZnO:Dy nanoparticles may be interpreted by the contribution of the magnetic moments from the unpaired 4f electrons of Dy3+ ions.

Recent progress of rare earth-based multi-modal nano-sized contrast agents

Due to the specific electron structure, distinctive optical/electronic/magnetic properties, and related high atomic number, worldwide scientists in various relevant fields have focused on the rational design of rare earth-based nano-sized contrast agents and their biomedical imaging application recently. For a long time, rare earth-doped nanoprobes have been widely used in up-conversion luminescence imaging owing to their attractive 4f electrons. Gd3+-modified nanoprobes and Gd3+-based nanomaterials with the unpaired 4f electrons have been generally used as contrast agents for T1-weighted MR imaging. In addition, rare earth-based nanosturcturs have performed well in X-ray imaging and CT imaging due to their stronger X-ray attenuation and higher atomic number than those of routinely used small iodinated molecules. This review provides a comprehensive introduction to the recent development of novel rare earth-based multi-modal nano-sized contrast agents, and their usages in the field of biomedical imaging.

Structural, electronic and magnetic properties of RE3+-doping in CoFe2O4: A first-principles study

RE3+(RE=La, Ce, Pr, Nd, Eu, Gd) doped cobalt ferrite (CoFe2O4) have been studied systematically by the first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA+U) . The significant effects of RE3+doping on the crystal structure, electronic and magnetic properties of CoFe2O4 have been explored. The calculated results show that the RE ions prefer substituting Fe3+ located at the octahedral sites. And the lattice constant of CoFe1.875RE0.125O4 (RE=La, Ce, Pr, Nd, Eu and Gd) decreases due to the decreasing ionic radius of RE as the atomic number increases. The magnetic properties depend on the unpaired 4f electrons of RE3+ ions. The net magnetic moment of CoFe2O4 increases by doping with Eu and Gd, the reason is that there are more unpaired 4f electrons for Eu3+and Gd3+. However, the net magnetic moment of CoFe2O4 decreases by doping with La, Ce, Pr, and Nd, due to the reason that these RE ions prefer their low spin configurations.

Achieving room temperature ferromagnetism in ZnS nanoparticles via Eu3+ doping

This paper reports the structural as well as the magnetic properties of ZnS:Eu3+ (0, 1, 2, 3, and 4at%) nanoparticles prepared by a hydrothermal method. The compositional, structural and magnetic properties of ZnS:Eu3+ nanoparticles were investigated by energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM) measurements. XRD studies confirmed that all the samples had a cubic structure with good crystallinity. TEM showed that the particles were polycrystalline with a mean size of 5–8nm. XPS revealed the oxidation state of the Eu in the ZnS lattice to be +3. All the Eu3+ -doped ZnS nanoparticles exhibited room temperature ferromagnetic behavior as a function of doping concentration. The observed RTFM may be interpreted by the contribution of the magnetic moments from the unpaired 4f electrons of Eu3+ in the ZnS:Eu3+ nanoparticles. The interesting magnetic properties of ZnS:Eu3+ nanoparticles may be further explored for new generation spintronic devices.

The new Zintl phases Eu21Cd4Sb18 and Eu21Mn4Sb18

Crystals of two new Zintl compounds, Eu21Mn4Sb18 and Eu21Cd4Sb18 have been synthesized using the molten metal flux method, and their structures have been established by single-crystal X-ray diffraction. Both compounds are isotypic and crystallize in the monoclinic space group C2/m (No. 12, Z=4). The structures are based on edge- and corner-shared MnSb4 or CdSb4 tetrahedra, which make octameric [Mn8Sb22] or [Cd8Sb22] polyanions. Homoatomic Sb–Sb bonds are present in both structures. The Eu atoms take the role of Eu2+cations with seven unpaired 4f electrons, as suggested by the temperature-dependent magnetization measurements. The magnetic susceptibilities of Eu21Mn4Sb18 and Eu21Cd4Sb18 indicate that both phases order anti-ferromagnetically with Néel temperatures of ca. 7K and ca. 10K, respectively. The unpaired 3d electrons of the Mn atoms in Eu21Mn4Sb18 do contribute to the magnetic response, however, the bulk magnetization measurements do not provide evidence for long-range ordering of the Mn spins down to 5K. Electrical resistivity measurements suggest that both compounds are narrow band gap semiconductors.

Dual-mode T1 and T2 magnetic resonance imaging contrast agent based on ultrasmall mixed gadolinium-dysprosium oxide nanoparticles: synthesis, characterization, and in vivo application

A new type of dual-mode T1 and T2 magnetic resonance imaging (MRI) contrast agent based on mixed lanthanide oxide nanoparticles was synthesized. Gd3+ (8S7/2) plays an important role in T1 MRI contrast agents because of its large electron spin magnetic moment resulting from its seven unpaired 4f-electrons, and Dy3+ (6H15/2) has the potential to be used in T2 MRI contrast agents because of its very large total electron magnetic moment: among lanthanide oxide nanoparticles, Dy2O3 nanoparticles have the largest magnetic moments at room temperature. Using these properties of Gd3+ and Dy3+ and their oxide nanoparticles, ultrasmall mixed gadolinium-dysprosium oxide (GDO) nanoparticles were synthesized and their potential to act as a dual-mode T1 and T2 MRI contrast agent was investigated in vitro and in vivo. The D-glucuronic acid coated GDO nanoparticles (davg = 1.0 nm) showed large r1 and r2 values (r2/r1 ≈ 6.6) and as a result clear dose-dependent contrast enhancements in R1 and R2 map images. Finally, the dual-mode imaging capability of the nanoparticles was confirmed by obtaining in vivo T1 and T2 MR images.