Magnetic Anisotropy of Maghemite Nanoparticles Probed by RF Transverse Susceptibility

AbstractWe present radio frequency magnetic transverse susceptibility measurements on γ-Fe2O3 nanoparticles, which yield an estimation of their effective anisotropy constant, Keff as a function of nanoparticle size. The resulting values range from 4 to 8 × 104 erg/cm3, being on the order of the magnetocrystalline anisotropy in bulk maghemite. Keff values increase as the particle diameter increases. Evidences of anisotropy field distribution given by the size distribution in the samples, and interparticle interactions that increase as the particle size increases, are also observed in the TS measurements. The effects of such interparticle interaction overcome those of thermal fluctuations, in contrast with the behavior of other iron oxide particles

Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles

We study, by means of magnetic susceptibility and magnetic aging experiments, the nature of the glassy magnetic dynamics in arrays of Co nanoparticles, self-organized in N layers from N=1 (two-dimensional limit) up to N=20 (three-dimensional limit). We find no qualitative differences between the magnetic responses measured in these two limits, in spite of the fact that no spin-glass phase is expected above T=0 in two dimensions. More specifically, all the phenomena (critical slowing down, flattening of the field-cooled magnetization below the blocking temperature and the magnetic memory induced by aging) that are usually associated with this phase look qualitatively the same for two-dimensional and three-dimensional arrays. The activated scaling law that is typical of systems undergoing a phase transition at zero temperature accounts well for the critical slowing down of the dc and ac susceptibilities of all samples. Our data show also that dynamical magnetic correlations achieved by aging a nanoparticle array below its superparamagnetic blocking temperature extend mainly to nearest neighbors. Our experiments suggest that the glassy magnetic dynamics of these nanoparticle arrays is associated with a zero-temperature spin-glass transition.Comment: 6 pages 6 figure

Residuo de Camarón Siete Barbas, como abono orgánico en el cultivo de tomate

The research was developed in order to evaluate the tomato seedlings behaviour (Lycopersiconesculentum mill) of the variety breastplate 98, under different dosages of compost made from seabob shrimp waste (Xiphopenaeuskroyeri). The experiment took place in the community of Rocky Point, Municipality of Pearl Lagoon, where the nature of the experiment is classified as a unifactorial arrangement, using an experimental design of randomized complete block (RCB) with 4 treatments and 3 repetitions. The variables evaluated were for: height of the plant (cm), stem diameter (cm) and production percentage (kg). The variables were submitted to an analysis of variance (ANOVA), obtaining 95% of reliance and multiple range tests according to Tukey's criterion with 0.05 for mean separation.   The greatest height of the seedlings (aerial part) was with treatment 3 (T3) with 250 g/plant, the second best value of height corresponded to treatment 2 (T2) with 350 g/plant, followed by the treatments 4 (T4) with 150 g/plant and treatment 1 (T1) as a baton. Regarding the diameter, we observed that during the first 45 days after sowing, the T3 (250g) and T3 (350) showed no significant difference, being the groups that obtained the best behaviour, followed by T4 (150 g) and T1 (baton). As for the tomato seedlings behaviour, it was similar to the diameter where T2 and T3 presented better crop production, followed by T4 and T1.La investigación se desarrolló con la finalidad de evaluar el comportamiento de plántulas de tomate (Lycopersiconesculentum mill) de la variedad peto 98 bajo diferentes dosificaciones de abono orgánico elaborado a base de desechos de camarón siete barbas (Xiphopenaeuskroyeri). El experimento se llevó a cabo en la comunidad de Rocky Point, Municipio de Laguna de Perlas, en donde la naturaleza del experimento se cataloga como un arreglo unifactorial, empleándose un diseño experimental de bloques completamente al azar (BCA), con 4 tratamientos y 3 repeticiones. Las variables evaluadas correspondieron a: altura de la planta (cm), diámetro de tallo (cm) y porcentaje de rendimiento (Kg), las variables se sometieron a un análisis de varianza (ANDEVA)  con un 95% de confianza y prueba de rangos múltiples según el criterio de Tukey con 0.05 para la separación de medias. La mayor altura (parte aérea) de las plántulas fue con el tratamiento 3 (T3) con 250 g/planta, el segundo mejor valor de altura correspondió al tratamiento 2 (T2) con 350g/planta, seguido de los tratamientos 4 (T4), con 150 g/planta) y tratamiento 1 (T1) como testigo. Con respecto al diámetro se observó que en los primeros 45 días después de la siembra los T3 (250g) y T3 (350),  no muestran diferencias significativas siendo los tratamientos en donde se obtuvo un mejor comportamiento, seguido de los T4 (150 g) y T1 (testigo), en cuanto a rendimiento de las plántulas de tomate, el comportamiento fue similar al diámetro en donde los T2 y T3, presentan mejores rendimientos en cosecha, seguidos por los T4 y T1

Achieving a "SIL 1" TCR Monitoring System

SIL 1 (Safety Integrity Level 1) refers to the quantification and measurement of the availability, reliability, maintenance and safety of the monitoring system. In the last few years the computer infrastructure used to acquire and to diffuse data to the TCR has evolved very rapidly. A number of measures in hardware, software and management have been introduced to cope with this situation. These include: the Multipurpose Monitoring Device (MMD), a standard data acquisition platform used in the renovation of old front end monitoring equipment, the Smart Equipment Controller (Dsec), a driver that reduces the layers in the data diffusion pyramid, the multiplatform monitoring software to integrate the different SCADA systems, a software configuration tool (RAZOR) for problem tracking and version control, and a complete development environment reproducing a real installation for thorough testing of any changes. To achieve SIL 1 objectives, while mastering the evolution of our systems will be the challenge for the computer team

Quadrupolar XMCD at the Fe K -edge in Fe phthalocyanine film on Au: Insight into the magnetic ground state

The observation of an anomalous quadrupolar signal in x-ray magnetic circular dichroism (XMCD) at the Fe K-edge of iron phthalocyanine (FePc) films is reported. All ground states previously suggested for FePc are incompatible with the experimental data. Based on ab initio molecular orbital multiplet calculations of the isolated FePc molecule, we propose a model for the magnetic ground state of the FePc film that explains the XMCD data and reproduces the observed values of the orbital moments in the perpendicular and planar directions

Intracluster interactions in butterfly {Fe3 LnO2} molecules with the non-Kramers ions Tb(III) and Ho(III)

The intracluster exchange interactions within the "butterfly" Fe3Ln(µ3-O)2(CCl3COO)8(H2O)(THF)3] molecules, where Ln(III) represents a lanthanide cation, have been determined by a combination of x-ray magnetic circular dichroism (XMCD) and vibrating sample magnetometry (VSM) along with an interaction model. We have studied the compounds with Ln=Tb and Ho, both non-Kramers lanthanides and with high uniaxial anisotropy, and Ln=Lu(III) and Y(III) as pseudolanthanides, which supply nonmagnetic Ln reference cases. At low temperature, the three Fe atoms can be considered as a self-unit with total spin SFe3=5/2. Using the element selectivity of the XMCD magnetometry, measured at the Ln L2,3 edges, together with the VSM measurements, the local magnetization of the Ln ion and the Fe3 subcluster, as a function of the field and low temperature (T˜2.5K), has been determined separately. These results are described quantitatively in the framework of a theoretical model based on an effective spin Hamiltonian, which considers the competing effects of intracluster interactions and the external applied magnetic field. The Ln-Fe3 exchange interaction within the {Fe3LnO2} cluster has been determined to be antiferromagnetic, in both Tb and Ho compounds, with JFeTb/kB=-0.13(1)K and JFeHo/kB=-0.18(1)K, respectively. In both cases, a field-induced reorientation of the Fe3 and Ln spins from antiparallel to parallel orientation takes place at a threshold field µ0H=1.1 and 2 T, for the {Fe3TbO2} and {Fe3HoO2} compounds, respectively. By comparison with other compounds of the series with uniaxial anisotropy, it is concluded that the polarizability of the Fe3 subcluster magnetic moment decreases in the trend {Fe3YO2}¿{Fe3TbO2}¿{Fe3HoO2}¿{Fe3DyO2}, because of the increasing opposition of the exchange antiferromagnetic field caused by the Ln ion. In the Ln=Tb, Ho, and Dy, the magnetization of the whole molecule is dominated by the anisotropy of the Ln ion. The intracluster Fe3-Ln exchange interactions are very weak compared to the Ln ligand field and Fe-Fe exchange interactions

Perpendicular magnetic anisotropy and intralayer interactions in a single layer of CoPt nanoparticles

The multilayer films Al2O3/tCo Co/tPt Pt]N, produced by sequential deposition of Co and Pt on alumina consist in layers of CoPt alloyed nanoparticles. They show perpendicular magnetic anisotropy (PMA) below a freezing temperature Tf, an asperomagnetic-like phase below that temperature, and hard ferromagnetic ordering below a transition temperature T1 < Tf. A single layer granular film (N = 1) with deposition thicknesses tCo=0.7 nm, tPt=1.5 nm and particle diameter of 3 nm is presently studied. SQUID magnetometry shows that a single layer presents the three phases as well. Para-, aspero-and ferromagnetic phases are observed upon lowering the temperature, with transition temperatures Tf ˜ 375 K and T1 ˜ 200 K, respectively. In addition, the PMA persists, proving that there is no interlayer coupling in the multilayer system. SQUID results also reveal a core-shell structure in the CoPt nanoparticles

Intracluster interactions in butterfly {Fe3 LnO2} molecules with the non-Kramers ions Tb(III) and Ho(III)

The intracluster exchange interactions within the >butterfly> [Fe3Ln(μ3-O)2(CCl3COO)8(H2O)(THF)3] molecules, where Ln(III) represents a lanthanide cation, have been determined by a combination of x-ray magnetic circular dichroism (XMCD) and vibrating sample magnetometry (VSM) along with an interaction model. We have studied the compounds with Ln=Tb and Ho, both non-Kramers lanthanides and with high uniaxial anisotropy, and Ln=Lu(III) and Y(III) as pseudolanthanides, which supply nonmagnetic Ln reference cases. At low temperature, the three Fe atoms can be considered as a self-unit with total spin SFe3=5/2. Using the element selectivity of the XMCD magnetometry, measured at the Ln L2,3 edges, together with the VSM measurements, the local magnetization of the Ln ion and the Fe3 subcluster, as a function of the field and low temperature (T≈2.5K), has been determined separately. These results are described quantitatively in the framework of a theoretical model based on an effective spin Hamiltonian, which considers the competing effects of intracluster interactions and the external applied magnetic field. The Ln-Fe3 exchange interaction within the {Fe3LnO2} cluster has been determined to be antiferromagnetic, in both Tb and Ho compounds, with JFeTb/kB=-0.13(1)K and JFeHo/kB=-0.18(1)K, respectively. In both cases, a field-induced reorientation of the Fe3 and Ln spins from antiparallel to parallel orientation takes place at a threshold field μ0H=1.1 and 2 T, for the {Fe3TbO2} and {Fe3HoO2} compounds, respectively. By comparison with other compounds of the series with uniaxial anisotropy, it is concluded that the polarizability of the Fe3 subcluster magnetic moment decreases in the trend {Fe3YO2}→{Fe3TbO2}→{Fe3HoO2}→{Fe3DyO2}, because of the increasing opposition of the exchange antiferromagnetic field caused by the Ln ion. In the Ln=Tb, Ho, and Dy, the magnetization of the whole molecule is dominated by the anisotropy of the Ln ion. The intracluster Fe3-Ln exchange interactions are very weak compared to the Ln ligand field and Fe-Fe exchange interactions.The projects MINECO (MAT2011/23791, MAT2011/27233-C02-02, and MAT2014/53921-R), DGA IMANA E34, and Alexander Von Humboldt Foundation (D.P.) are acknowledged for financial support.Peer Reviewe

Quadrupolar XMCD at the Fe K -edge in Fe phthalocyanine film on Au: Insight into the magnetic ground state

Under the terms of the Creative Commons Attribution license.-- et al.The observation of an anomalous quadrupolar signal in x-ray magnetic circular dichroism (XMCD) at the Fe K-edge of iron phthalocyanine (FePc) films is reported. All ground states previously suggested for FePc are incompatible with the experimental data. Based on ab initio molecular orbital multiplet calculations of the isolated FePc molecule, we propose a model for the magnetic ground state of the FePc film that explains the XMCD data and reproduces the observed values of the orbital moments in the perpendicular and planar directions.The financial support of the Spanish financial agency MINECO MAT2011-23791 and MAT2014-53921-R, Aragonese DGA-IMANA E34 (co-funded by Fondo Social Europeo), and European Union FEDER funds is acknowledged. The research at UCSD was supported by the Office of Basic Energy Science, US Department of Energy, BES-DMS, funded by the Department of Energy Office of Basic Energy Science, DMR, under Grant No. DE FG03 87ER-45332.Peer Reviewe