Temperature Electron Paramagnetic Resonance Research Articles

Short-range magnetic correlation, metamagnetism, and coincident dielectric anomaly in Na5Co15.5Te6O36

Here we explore the structural, magnetic and dielectric properties of Co based compound Na$_5$Co$_{15.5}$Te$_6$O$_{36}$ as a candidate of short-range magnetic correlations driven development of dielectric anomaly above N$\acute{e}$el temperature of ($T_N$=) 50 K. Low temperature neutron powder diffraction (NPD) in zero applied magnetic field clearly indicates that the canted spin structure is responsible for the antiferromagnetic transition and partially occupied Co form short range magnetic correlation with other Co, which further facilitates the structural distortion and consequent development of dielectric anomaly above antiferromagnetic transition. Additionally, the temperature dependent magnetic heat capacity and electron spin resonance measurements reveal the presence of short-range magnetic correlations which coincides with an anomaly in the dielectric constant vs temperature curve. Moreover, significant changes in the lattice parameters are also observed around the same temperature, indicating presence of noticeable spin-lattice coupling. Further, sharp jump in the magnetic field dependent magnetization clearly indicates the presence of metamagnetic transition and magnetic field dependent NPD confirms that rotations of Co spins with applied magnetic field are responsible for this metamagnetic phase transition. As a result, this transition causes the magnetocaloric effect to be developed in the system, which is suitable for the application in low temperature refrigeration.

Electron spin resonance in P-doped Si nanocrystals/SiC stacked structures with various dot sizes

Doping in semiconductor nanocrystals have a significant impact on electronic structures and the relative studies are needed in order to deeply understand the doping effect in nanoscale. Here, we fabricate un-doped and P-doped Si nanocrystals (Si NCs)/Silicon carbide (SiC) multilayers with various dot sizes (8, 4 and 2 nm). Low temperature (77 K) electron spin resonance spectra are measured to study the electronic structures before and after P doping. It is found that the g value is kept at 2.005 for un-doped Si NCs samples, which is independent of the dots size, indicating the existence of dangling bonds at the surface of Si NCs. After P doping, for samples with dot size of 8 nm, the g value is 1.998, which is assumed to the conduction electrons. It suggests that P impurities are introduced into the inner of Si NCs substitutionally to provide the conduction electrons. However, with the reduction of dot size, the signals with g = 2.004, which is associated with the Si vacancies, are identified in P-doped samples, while the peak-to-peak linewidth ΔBpp is narrowed with the dots size decreasing. It shows the possibility to apply P-doped Si NCs/SiC multilayers with ultra-small dot sizes into Si-based spintronics.

Development of a scanning tunneling microscope for variable temperature electron spin resonance.

Recent advances in improving the spectroscopic energy resolution in scanning tunneling microscopy (STM) have been achieved by integrating electron spin resonance (ESR) with STM. Here, we demonstrate the design and performance of a homebuilt STM capable of ESR at temperatures ranging from 1 to 10K. The STM is incorporated with a homebuilt Joule-Thomson refrigerator and a two-axis vector magnet. Our STM design allows for the deposition of atoms and molecules directly into the cold STM, eliminating the need to extract the sample for deposition. In addition, we adopt two methods to apply radio-frequency (RF) voltages to the tunnel junction: the early design of wiring to the STM tip directly and a more recent idea to use an RF antenna. Direct comparisons of ESR results measured using the two methods and simulations of electric field distribution around the tunnel junction show that, despite their different designs and capacitive coupling to the tunnel junction, there is no discernible difference in the driving and detection of ESR. Furthermore, at a magnetic field of ∼1.6T, we observe ESR signals (near 40GHz) sustained up to 10K, which is the highest temperature for ESR-STM measurement reported to date, to the best of our knowledge. Although the ESR intensity exponentially decreases with increasing temperature, our ESR-STM system with low noise at the tunnel junction allows us to measure weak ESR signals with intensities of a few fA. Our new design of an ESR-STM system, which is operational in a large frequency and temperature range, can broaden the use of ESR spectroscopy in STM and enable the simple modification of existing STM systems, which will hopefully accelerate a generalized use of ESR-STM.

Essential Role of Triplet Diradical Character for Large Magnetoresistance in Quinoidal Organic Semiconductor with High Electron Mobility.

A diradicaloid molecule with high semiconducting performance is synthesized based on the quinoidal benzo[1,2‐b:4,5‐b′]dithiophene structure. The diradical character is investigated by quantum chemical calculations and variable temperature electron spin resonance. The diode devices based on this molecule show a large change in electric current in magnetic fields below 100 mT with a strong dependence on the measurement temperatures; as the population of the triplet diradicals increases at high temperatures, the magnetoconductance (MC) values increase. As a result, a MC of −19.4% is achieved at 120 °C, which is the largest negative MC observed for organic molecules to date. In contrast, a smaller diradicaloid molecule based on quinoidal thieno[3,2‐b]thiophene without thermally accessible triplet state shows no MC, indicating the essential role of the triplet diradicals. The strong correlation between the MC and the triplet diradical concentrations suggests that the charge conduction in the diradicaloid is suppressed through a spin‐blocking mechanism, which can be controlled through the magnetic modulation of the hyperfine fields. The compound forms high‐crystallinity thin films and has high monopolar electron transport in organic field‐effect transistors, with an average mobility of 1.01 cm2 V−1 s−1 for edge‐cast films.

Photocatalytic performance of rich OVs-BiOCl modified by polyphenylene sulfide

Introduction of oxygen vacancies (OVs) on the surface of photocatalyst has been proved to be a potent avenue to improve photocatalytic capability by accelerating the segregation of photoactivated carriers and creating a defect energy level. In this presentation, a facile hydrothermal approach was performed to fabricate polyphenylene sulfide (PPS)/OVs-BiOCl composites to further improve the catalytic capability of OVs enriched BiOCl. The successful construction of rich OVs in BiOCl was firmly confirmed by X-ray photoelectron spectroscopy (XPS) and low- temperature electron spin resonance (ESR). Surface photovoltage spectrum (SPS) and electrochemical characterization display that the existence of PPS in the synthetic system dramatically affects the surface states of BiOCl, expediting the segregation of photoinduced carriers. Photocatalytic capacity of PPS/OVs-BiOCl was examined by disintegration of perfluorooctanoic acid (PFOA), rhodamine B (RhB) and tetracycline (TC). PPS surface modification can significantly improve the photoactivity of OVs-BiOCl toward destruction of PFOA, RhB and TC. Interestingly, when mass ratio of PPS/BiOCl is 0.5%, the degradation capacity of PPS/OVs-BiOCl for decontamination of RhB and TC is 4.25 and 3.10 -fold higher than that of OVs-BiOCl, respectively. In consideration of the observations, the photocatalytic enhancement mechanism for PPS/OVs-BiOCl was elaborated.

Excellent visible light responsive photocatalytic behavior of N-doped TiO2 toward decontamination of organic pollutants

In this work, N-doped TiO2 (N-TiO2) with ample and tunable OVs was successfully synthesized, deriving from facile hydrothermal method and baked in the NH3 atmosphere. N-doping boosts the amount of surface hydroxyl and superoxide (O2−) of TiO2, demonstrated by XPS and nitroblue tetrazolium (NBT)-O2− quantitative reaction. Rich and tunable OVs were confirmed by low temperature electron spin resonance (ESR) results, demonstrating that doping of N into TiO2 can definitely construct higher OVs than the reference TiO2. Surface photovoltage spectrum (SPS) test, fluorescence experiments and electrochemical measurements all display that N-TiO2 photocatalysts with OVs have a higher severance efficiency of photogenerated e-/h+ pairs than the pristine TiO2. Photocatalytic evaluation results exhibit that N-TiO2 photocatalysts demonstrate better performance than the reference TiO2 toward decontamination of rhodamine B and tetracycline. TiO2 treated in ammonia atmosphere for 1 h shows the highest photocatalytic property. The visible light responsive catalytic behavior of TiO2 treated in ammonia atmosphere for 1 h is much higher than that of commercial TiO2 (P25) and the pristine TiO2, separately. The ameliorated visible light behavior of N-TiO2 photocatalysts is attributable to rich oxygen vacancies produced through introducing N into TiO2 and the boosted severance of photoactivated e-/h+.

Ultrathin nanoflake-assembled hierarchical BiOBr microflower with highly exposed {001} facets for efficient photocatalytic degradation of gaseous ortho-dichlorobenzene

A series of BiOBr catalysts with different microstructures were synthesized by tuning the solvothermal conditions. Assisted by the surface photovoltage, transient photovoltage and time-resolved photoluminescence techniques, the photoexcited charge carriers separation and transfer dynamics were comparatively investigated. The results indicated that the hierarchical BiOBr microflower (BiOBr MF) consisting of well-organized ultrathin nanoflakes were most efficient in promoting charge carrier separation and migration, resulting from the nearly 100 % {001} facets exposed with more oxygen defects. Furthermore, the photocatalytic performance was estimated through the degradation of gaseous ortho-dichlorobenzene (o-DCB) under visible light irradiation, and the BiOBr MF exhibited superior photoactivity. The enhanced mechanism underlying the charge transfer was disclosed by the energy band structures and the reactive oxygen species which were examined by room temperature electron spin resonance. In addition, the catalytic oxidation process of o-DCB over the BiOBr MF and the corresponding surface intermediates was revealed by in situ FTIR spectroscopy.

Anisotropy-Induced Soliton Excitation in Magnetized Strong-Rung Spin Ladders.

We report low temperature electron spin resonance experimental and theoretical studies of an archetype S=1/2 strong-rung spin ladder material (C_{5}H_{12}N)_{2}CuBr_{4}. Unexpected dynamics is detected deep in the Tomonaga-Luttinger spin liquid regime. Close to the point where the system is half-magnetized (and believed to be equivalent to a gapless easy plane chain in zero field) we observed orientation-dependent spin gap and anomalous g-factor values. Field theoretical analysis demonstrates that the observed low-energy excitation modes in magnetized (C_{5}H_{12}N)_{2}CuBr_{4} are solitonic excitations caused by Dzyaloshinskii-Moriya interaction presence.

Charge-Order Phase Transition in the Quasi One-Dimensional Organic Conductor {hbox {(TMTTF)}}_2 {hbox {NO}}_3

Low-dimensional organic conductors show a rich phase diagram, which has, despite all efforts, still some unexplored regions. Charge ordered phases present in many compounds of the {hbox {(TMTTF)}}_2X family are typically studied with their unique electronic properties in mind. An influence on the spin arrangement is, however, not expected at first glance. Here, we report temperature and angle dependent electron spin resonance (ESR) measurements on the quasi one-dimensional organic conductor {hbox {(TMTTF)}}_2 {hbox {NO}}_3. We found that the {hbox {(TMTTF)}}_2 {hbox {NO}}_3 compound develops a peculiar anisotropy with a doubled periodicity (ab'-plane) of the ESR linewidth below about T_{text {CO}}= ({250pm 10})~hbox {K}. This behavior is similar to observations in the related compounds {hbox {(TMTTF)}}_2X (X = {hbox {PF}}_6, {hbox {SbF}}_6 and {hbox {AsF}}_6), where it has been attributed to relaxation processes of magnetically inequivalent sites in the charge-ordered state. For the structural analogous {hbox {(TMTTF)}}_2 {hbox {ClO}}_4, known for the absence of charge order, such angular dependence of the ESR signal is not observed. Therefore, our ESR measurements lead us to conclude that a charge-order phase is stabilized in the title compound below T_{text {CO}} approx 250~hbox {K}.

One-pot solvothermal fabrication of S-scheme OVs-Bi2O3/Bi2SiO5 microsphere heterojunctions with enhanced photocatalytic performance toward decontamination of organic pollutants

Bi2O3/Bi2SiO5 microsphere heterojunctions self-assembled by nanoplatelets with rich oxygen vacancies (OVs) were fabricated through a mild one-step solvothermal approach. The existence of OVs was confirmed by XPS and low temperature electron spin resonance (ESR) technique. The crystal texture, morphology, and optical property of the 3D OVs-Bi2O3/Bi2SiO5 microsphere heterojunctions were analyzed by a series of characterization methods. The results reveal that OVs-Bi2O3/Bi2SiO5 heterojunctions were constructed and the diameter of microspheres is about 1 μm. The photocatalytic performance of OVs-Bi2O3/Bi2SiO5 composite microspheres was assessed using methyl orange (MO) and colorless phenol as model contaminant. The synergistic effect of Bi2O3 and Bi2SiO5 greatly enhances the removal rates of organic pollutants. O2– and h+ are predominant active free radicals in the photocatalytic process, supporting by ESR, nitroblue tetrazolium (NBT) and trapping experiments. The separation and transfer of the photoinduced charge pairs of OVs- Bi2O3/Bi2SiO5 heterojunctions follow a step-scheme mechanism. The step-scheme mechanism endows OVs-Bi2O3/Bi2SiO5 heterojunctions with higher photocatalytic performance than the bare Bi2SiO5.

Spin Fluctuations at the Surface of Strongly Correlated Topological Insulator SmB6

The low temperature (T < 5 K) electron spin resonance in topological Kondo insulator SmB6 is investigated. It is shown that spin relaxation time of the paramagnetic centers responsible for low temperature electron spin resonance in SmB6 is about ~ 10−8 s, which exceeds by five orders of magnitude the widely accepted spin and charge fluctuation time ~ 10−13 s in the homogeneous mixed valence state of this material. This discrepancy may be attributed to the formation of the specific paramagnetic centers in the sample surface–spin polarons.

Preparing a photocatalytic Fe doped TiO2/rGO for enhanced bisphenol A and its analogues degradation in water sample

For extending the light response to visible spectrum, an approach to efficient photocatalysts in sustainable energy technology has been a hot research topic. In this work, Fe doped TiO2/rGO (Fe-TiO2/rGO) was synthesized via one-step hydrothermal deposition method. The presence of Fe-Ti bond and Ti3+ in the photocatalyst was confirmed by XPS, EXAFS and Raman analyses. The batch experiments showed that as-synthesized Fe-TiO2/rGO nanocomposites exhibited high photocatalytic performance for bisphenol A (BPA) and its analogues degradation under visible light irradiation (λ ≥ 420 nm). Moreover, Fe-TiO2/rGO presented high photocatalytic activity at a high BPA concentration of 95 ppm as well as a wide pH value of 4.5–8.5. Additionally, the extended visible light absorption range Fe-TiO2/rGO was demonstrated by low temperature electron spin resonance, UV–vis diffuse reflectance spectra, the transient photocurrent density and electrochemical impedance spectroscopies measurements. The radical quenching and ESR active species trapping experiments implied the main role of superoxide radicals on the high efficient photodegradation of BPA. These findings are crucial for designing TiO2-based photocatalysts with high performance for degradation of persistent organic pollutants in wastewater treatment.

Aging-Resistant Behavior and Room Temperature Electron Spin Resonance of Nd3+ in Singly and Doubly Doped BaTiO₃ Ceramics Associated with Preservation History.

The (Ba0.96Nd0.04)Ti0.99O3 (BN4T) and (Ba0.96Nd0.04)(Ti0.94Ce0.05)O3 (BN4TC5) ceramics were prepared via the mixed oxide route exhibited tetragonal and pseudo-cubic structures, respectively. After they were preserved over a long period of time, a broader electron spin resonance (ESR) signal at g = 2.338 and a narrow ESR signal at g = 2.151 were detected at room temperature (RT) for BN4T and BN4TC5, respectively. They most likely originated from the Nd3+ Kramers ions in BN4T and Nd3+-Ce4+ defect complexes in BN4TC5 ceramics, respectively. The origins of these two ESR signals and the aging-resistant dielectric behavior are further discussed.

Thermal evolution of impurities and hydroxyl groups in ZnO nanocrystals

Impurities and surface hydroxyl groups play vital roles in tailoring the physicochemical properties of metal oxides. Herein, commercial ZnO nanocrystals (Sigma-Aldrich) were selected to trace the impurity and hydroxyl group evolution by temperature dependent photoluminescence spectrum, infrared spectrum and electron spin resonance spectrum. It is found that the structured Cu impurity emission in ZnO appeared when the temperature is down to 100 K. As thermal annealing reduced the donors significantly, the corresponding 5780 cm−1 and 5820 cm−1 IR peaks can be observed when the annealing temperature is above 600 °C. Further annealing at 800 °C increases the Cu2+ concentration as well as activates the diffusion of lithium impurity, both of which contribute to the visible luminescence. Besides, a group of IR peaks in the range of 3400–3700 cm−1 were found to be vanished after 800 °C thermal annealing, demonstrating their hydroxyl features rather than the previously proposed defect origin.

Magnetism in BiFe1−xNixO3: studied through electron spin resonance spectroscopy

The effect of Ni doping in BiFe1−xNixO3 (BFNO) multiferroics are studied by X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), hysteresis loop (M–H), temperature dependent magnetization (FC-ZFC) measurements and electron spin resonance (ESR) techniques. The XRD and FTIR studies indicate that the BFNO compounds remain in rhombohedral (R3c) phase without appearance of any structural transformation due to Ni doping. The XPS studies show the oxidation states of Fe ions as 3+, whereas Bi is found to be in a mixed valence state of 2+ and 3+ in BFNO. The Ni ion doping enhances the saturation magnetization from 0.179 emu/g (x = 0.025) to 2.38 emu/g (x = 0.20), which is higher than the reported values found in literature. The FC-ZFC magnetization studies suggest the presence of a magnetic phase transition from a weak ferromagnetic to a spin glass state at low temperature. The ESR studies confirm the ferromagnetic state of BFNO samples.

Enhancement of ferromagnetic properties in composites of BaSnO3 and CoFe2O4

In this paper, we report structural and magnetic properties of BaSnO3(BSO)(1−x)–CoFe2O4 (CFO)(x) composite (with x = 0%, 1% (C1), 2% (C2) and 5% (C3) in molar ratio) synthesized using nitrate precursor method. The X-ray diffraction (XRD) pattern of the composite powder confirmed presence of both BaSnO3 with the cubic perovskite structure and CoFe2O4 with the cubic spinel structure. No signature of any other phases in pure BaSnO3, CoFe2O4 and composites have been detected either in XRD or energy dispersive X-ray (EDS) analysis. The temperature dependent zero field cooled (ZFC) & field cooled (FC) magnetization and magnetic field dependence magnetization measurements have been carried at room temperature of the pure BaSnO3. We observe a weak ferromagnetic (FM) behavior at room temperature in pure BaSnO3 even though it is non-magnetic in nature. The room temperature Raman spectroscopy and electron spin resonance measurements of the sample confirm the presence of oxygen vacancy and formation of F-center, which is responsible for the FM behavior. The oxidation state and elemental analysis have been carried out using X-ray photoelectron spectroscopy (XPS). The magnetic field dependence of magnetization of the composite samples reveal increase of saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) with increase in ferrite content in the composite. Significant enhancement in FM components is observed with lowering of temperature.

Crystal-field effects in Er3+ - and Yb3+ -doped hexagonal NaYF4 nanoparticles

Since the up-conversion phenomenon in rare-earths (REs) doped ${\mathrm{NaYF}}_{4}$ is strongly affected by the crystal electric field (CF), determining the CF parameters, wave functions, and scheme of the energy levels of the RE $J$ multiplets could be crucial to improve and tune the up-conversion efficiency. In this work, the temperature and magnetic field dependent magnetization of ${\mathrm{NaY}}_{1\ensuremath{-}x}{[\mathrm{Er}(\mathrm{Yb})]}_{x}{\mathrm{F}}_{4}$ hexagonal nanoparticles (NPs) is reported. The data were best fit using the appropriated CF Hamiltonian for the $J=15/2\phantom{\rule{0.16em}{0ex}}(J=7/2)$ ground state multiplet of ${\mathrm{Er}}^{3+}\phantom{\rule{0.16em}{0ex}}({\mathrm{Yb}}^{3+}$) ions. The ${B}_{2}^{0}, {B}_{4}^{0}, {B}_{6}^{0}$, and ${B}_{6}^{6}$ CF parameters were considered in the Hamiltonian for RE ions located at the hexagonal ${\mathrm{C}}_{3h}$ point symmetry site of the ${\mathrm{NaYF}}_{4}$ host lattice. These results allowed us to predict an overall CF splitting of $\ensuremath{\sim}214$ ($\ensuremath{\sim}356$ K) for ${\mathrm{Er}}^{3+}$ (${\mathrm{Yb}}^{3+}$) and the wave functions and their energy levels for the $J=15/2$ ($J=7/2$) ground state multiplet which are in good agreement with the low temperature electron spin resonance experiments. Besides, our measurements allowed us to calculate all the excited CF $J$ multiplets that yield to a good estimation of the up-conversion light emission linewidth. The nonlinear optical light emission of the studied ${\mathrm{NaY}}_{1\ensuremath{-}x}{[\mathrm{Er}(\mathrm{Yb})]}_{x}{\mathrm{F}}_{4}$ hexagonal NPs was also compared with the most efficient up-conversion codoped ${\mathrm{NaY}}_{1\ensuremath{-}x\ensuremath{-}y}{\mathrm{Er}}_{x}{\mathrm{Yb}}_{y}{\mathrm{F}}_{4}$ hexagonal NPs.

Importance of the Formation of Dy4+ in BaZr0.9Dy0.1O3-δ proton-Conducting Ceramics in Oxidizing Atmospheres

Yttrium doped barium zirconate, BaZr1-xYxO3-δ, has been one of the most studied high temperature proton conductors for the last two decades [1]. Several research groups focused on the choice of the trivalent dopant, which is necessary to create the oxygen vacancies required for the hydration of the material. Han et al. studied for example Sc, Sm, Eu and Dy dopants [2-4] and reported the presence of Dy4+in oxidizing atmospheres. In this work, we are interested in the comparison of structural and electrical properties between the well-known BZY10 (BaZr0.9Y0.1O3-δ) and BZDy10 (BaZr0.9Dy0.1O3-δ). A wide combination of experiments was used to confirm the presence of Dy4+ in oxidizing atmosphere, including high temperature X-ray diffraction, Raman spectroscopy, SQUID magnetometry and electron spin resonance (ESR or EPR). Figure 1 summarizes the BZDy10 lattice parameter in dry oxidizing atmosphere as a function of temperature and shows a decrease in the lattice parameter when increasing the oxygen partial pressure. This is explained by the difference in Dy radii in VI coordination: 0.78 Å and 0.912 Å for Dy4+ and Dy3+respectively. Conductivity measurements as a function of pO2in dry and moist conditions were performed for both BZY10 and BZDy10. The two materials behaved quite similarly in moist reducing atmosphere (i.e., pure ionic conduction), while significant differences were noticed in oxidizing atmospheres. [1] Fabbri E., Pergolesi D. and Traversa E., “Materials challenges toward proton-conducting oxide fuel cells: a critical review ”, Chem. Soc. Rev 39, 4355-4369 (2010) [2] D. Han, K. Shinoda, T. Uda, Dopant site occupancy and chemical expansion in rare earth-doped barium zirconate, J. Am. Ceram. Soc. 97 (2014) 643-650 [3] D. Han, T. Uda, Y. Nose, T. Okajima, H. Murata, I. Tanaka and K. Shinoda, Tetravalent Dysprosium in a Perovskite-Type Oxide, Advanced Materials 24 (2012) 2051-2053 [4] D. Han, K. Shinoda, S. Sato, M. Majima, T. Uda, Correlation between electroncutive and structural properties of proton conductive acceptor doped barium zirconate, J. Mater. Chem. A, 13 (2015) 1243-1250 Figure 1

Evaluation of sol–gel based magnetic 45S5 bioglass and bioglass–ceramics containing iron oxide

Multicomponent oxide powders with nominal compositions of (45−x)·SiO2·24.5CaO·24.5Na2O·6P2O5xFe2O3 (in wt.%) were prepared by a modified sol–gel procedure. X-ray diffraction (XRD) patterns and high resolution transmission electron microscope images of the sol–gel products show fully amorphous structure for Fe2O3 substitutions up to 2wt.%. Sol–gel derived 43SiO2·24.5CaO·24.5Na2O·6P2O5·2Fe2O3 glass (or bioglass 45S5 with SiO2 substituted with 2wt.% Fe2O3), exhibited magnetic behavior with a coercive field of 21Oe, hysteresis loop area of 33.25erg/g and saturation magnetization of 0.66emu/g at an applied field of 15kOe at room temperature. XRD pattern of this glass annealed at 850°C for 1h revealed the formation of a glass–ceramic containing sodium calcium silicate and magnetite phases in nanocrystalline form. Temperature dependent magnetization and room temperature electron spin resonance data have been used to obtain information on the magnetic phase and distribution of iron ions in the sol–gel glass and glass–ceramic samples. Sol–gel derived glass and glass–ceramic exhibit in-vitro bioactivity by forming a hydroxyapatite surface layer under simulated physiological conditions and their bio-response is superior to their melt quenched bulk counterparts. This new form of magnetic bioglass and bioglass ceramics opens up new and more effective biomedical applications.

Electron Spin Resonance Study on Room-Temperature Ferromagnetic La&lt;sub&gt;0.9&lt;/sub&gt;Sr&lt;sub&gt;0.1&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Nanoparticles

La 1−x Sr x MnO 3 half-metal manganites attract much attentions due to the colossal magnetoresistance (CMR) effect1 related to the Griffiths singularity2 with a critical percolation threshold (x=∼0.08). For a ferromagnetic (FM) insulating homogeneous phase of bulk La 0.9 Sr 0.1 MnO 3 (T C ∼ 150 K), the Griffiths phase which contains both FM and paramagnetic (PM) domains could be induced by intrinsic inhomogeneity at a transition temperature T G (275K) above T C .2 Such Griffiths phase could also be affected by the size of sample when the sample dimension is downscaled to nanometers. Previous studies reported many interesting phenomena related to size effects including the size-induced structural transition, core-shell phase separation and the enhancement of magnetization and exchange bias. However, the studies on nano-size effects are mostly focused on the doped metallic phase. Recently, room temperature ferromagnetism is reported in nano-sized insulating La 0.9 Sr 0.1 MnO 3 3 which remains to be understood. In this work, temperature dependent magnetization (M-T) and electron spin resonance (ESR) are investigated in La 0.9 Sr 0.1 MnO 3 nano-particles. ESR is a very sensitive probe to detect the core-shell phase separation and FM signal in Griffiths phase. The field dependent M-T results show the coexistence of multiple magnetic phases which is similar to Griffiths phase in bulk samples. Multiple lines appear in ESR spectra. By fitting with Lorenz/Gaussian functions, the multiple phases are identified as FM and PM states for 270 C and T G are enhanced in nano-sized La 0.9 Sr 0.1 MnO 3 comparing with bulk one. Based on our analysis, the size effect on the crystal structure of nanoparticle could be the cause for room-temperature ferromagnetism.