Direct observation of magnetization reversal of epitaxial MnAs films

The magnetization reversal of MnAs epitaxial films on GaAs (0 0 1) substrates was investigated using a Kerr microscope. The direct observation of the change in domain structure under magnetic fields revealed characteristic magnetization reversal process of MnAs films with a ladder-type domain structure. The nucleus of the magnetization reversal region appears and propagates to neighboring α-MnAs lines, and then the ladder-type structures cover all over the surface. Finally the domain wall displacement occurs to expand the domain. The change in magnetic domain reflects the characteristic ridge/groove structures of MnAs films.     

The magnetocaloric effect and low temperature specific heat of SmNi

The magnetocaloric effect (MCE) in a magnetic SmNi sample was evaluated from magnetization and heat capacity measurements. The MCE phenomena in the vicinity of magnetic phase transitions in terms of magnetic entropy change, , and adiabatic temperature change, , are reported. Isothermal magnetization measurements at several temperatures around the transition were carried out and used for versusT calculations. A similar dependence of the magnetic entropy change was evaluated from heat capacity C_p(T) measurements under zero field and 5 T. The SmNi system provides magnetic refrigerants that induce an adiabatic cooling of about during the magnetization process with a field of 5 T in the temperature range of 35-45 K. The temperature dependence of C_p(T) is analyzed in terms of the magnetic and the lattice contributions.     

Magnetic and superconducting properties of a pressure-induced superconductor CePd5Al2

We investigated the magnetic and electronic properties of an antiferromagnet and pressure-induced superconductor CePd₅Al₂ by measuring the magnetization and de Haas-van Alphen effect, together with the electrical resistivity under pressure and magnetic field. Magnetic measurements including the high field magnetization at 1.3 K reveal several magnetic transitions and quite complex magnetic phase diagram of this compound. Electrical resistivity measurements have been performed using diamond anvil cell up to 12 GPa for the magnetic fields and [1 0 0]. The upper critical field in superconductivity is anisotropic between and [1 0 0] in the tetragonal structure, reflecting the quasi-two dimensional electronic state.     

Elliptic quantum group , Hopf algebroid structure and elliptic hypergeometric series

We propose a new realization of the elliptic quantum group equipped with the H-Hopf algebroid structure on the basis of the elliptic algebra . The algebra has a constructive definition in terms of the Drinfeld generators of the quantum affine algebra and a Heisenberg algebra. This yields a systematic construction of both finite- and infinite-dimensional dynamical representations and their parallel structures to . In particular we give a classification theorem of the finite-dimensional irreducible pseudo-highest weight representations stated in terms of an elliptic analogue of the Drinfeld polynomials. We also investigate a structure of the tensor product of two evaluation representations and derive an elliptic analogue of the Clebsch–Gordan coefficients. We show that it is expressed by using the very-well-poised balanced elliptic hypergeometric series .     

Local magnetization study of the first-order superconducting transition in CeCoIn5

We report local magnetization measurements on the heavy fermion superconductor CeCoIn₅ using a micro-Hall probe. Below a critical point T₀ (), the local magnetization shows a clear jump at the superconducting transition temperatures for both H∥a and H∥c, indicating that the phase transition at the upper critical field H_c2 becomes a first-order phase transition. In addition, we observed an undershoot behavior of magnetization jump above (H∥c), which suggests a rapid change of textured superconducting structure with vortices and the nodal planes expected in the Fulde-Ferrell-Larkin-Ovchinnikov state.     

Mössbauer and magnetic studies in nickel ferrite nanoparticles: Effect of size distribution

The magnetic properties of nickel ferrite nanoparticles in the form of powders, prepared by the sol-gel process and subjected to different annealing temperatures, were investigated using both static and dynamic measurements namely hysteresis, zero field cooled-field cooled magnetization (ZFC-FC) measurements and Mössbauer spectroscopy. The Transmission Electron Microscopy (TEM) studies reveal particle sizes for the as-prepared particles which increases upto 52 nm with annealing. A bimodal distribution, upto an annealing temperature of was observed. ZFC-FC measurements for the as-prepared samples reveal twin peaks, indicative of the bimodal size distribution. ZFC-FC measurements performed for fields varying from 100 Oe to 3 kOe show a superparamagnetic phase with blocking temperatures between 320 and . Numerical simulations for the ZFC-FC studies indicate that the signature of the bimodal size distribution can be seen only at very low fields. The variation of coercivity with particle size, as determined from the hysteresis measurements, shows a transition from a single domain to a multi domain state for particle sizes larger than 35 nm. Mössbauer measurements performed at room temperature for the as-prepared sample shows a six finger pattern for the samples with higher particle size and a doublet pattern for the samples with smaller particle size, which is indicative of their superparamagnetic nature.     

Thermal and magnetothermal properties of La0.5Pr0.5Mn2Si2

The thermal and magnetothermal properties of La_0.5Pr_0.5Mn₂Si₂ and isostructural LaFe₂Si₂ intermetallic compounds in the temperature range 4.5-303 K are reported with and without applied magnetic field. The electronic, lattice, and magnetic contributions to the heat capacity of La_0.5Pr_0.5Mn₂Si₂ are determined and analyzed. We have determined and from heat capacity experiments; the values are in line with those from the magnetization measurements. We conclude that in order to observe the anomaly in the heat capacity data around in the system, the transition around should occur in a narrow temperature interval.     

Formation of room-temperature ferromagnetic Zn1−xCoxO nanocrystals

Optical and magnetic properties of Co²⁺-doped ZnO nanocrystals were studied. Optical measurements confirm the incorporation of Co²⁺ in ZnO lattice with tetrahedral geometry. Optical absorption spectra also reveal the partial bleaching of the excitonic feature attributable to an increase in electron concentration. Magnetization measurements indicate the ferromagnetic ordering in Co²⁺-doped ZnO nanocrystals with saturation magnetization . No structural changes were observed in lightly doped ZnO nanocrystals. The present investigations are important in obtaining the ferromagnetic Zn_1−xCo_xO nanocrystals.     

Magnetic properties of ErN films

We report a magnetization study of stoichiometric ErN nanocrystalline films grown on Si and protected by a GaN passivating layer. According to the temperature dependence of the resistivity the films are heavily doped semiconductors. Above 100 K the magnetization data fit well to a Curie-Weiss behavior with a moment expected within the free-ion Er³⁺ multiplet. Below 50 K the Curie-Weiss plot steepens to an effective moment corresponding to that in the crystal-field determined quartet ground state, and develops a clear paramagnetic Curie-Weiss temperature of about 4.5 K. Zero-field- and field-cooled magnetization curves and the AC susceptibility firmly establish a ferromagnetic ground state within that multiplet below a Curie temperature of . Due to the (1 1 1) texture of the film the comparison between the magnetization behavior, when the field is applied parallel and perpendicular to the film plane, gives new information about the magnetic structure. An arrangement of the moments according to the model derived from neutron diffraction for bulk HoN is strongly suggested.     

Fast weighting functions for retrievals from limb scattering measurements

The satellite-borne UV-visible-NIR spectrometers SCIAMACHY and OSIRIS perform operational measurements of the Earth's limb radiance with global coverage. The vertically resolved atmospheric composition is retrieved from the measurements. We have computed synthetic limb measurements and weighting functions (WFs) with several orders of scattering and surface reflection. Comparisons reveal the wavelength-dependent contributions of single scattering and the second orders of scattering and surface reflection. We have also performed test retrievals of the and profiles with the program package SCIARAYS. They prove that the single scattering approximation is sufficient for the calculation of the WFs during the retrieval process. We conclude that algorithms for the analysis of limb scattering measurements can be accelerated by neglecting higher orders of scattering in the WF calculations.     

Room temperature ferromagnetism in Zn-Mn-O

Zn-Mn-O semiconductor crystallites with nominal manganese concentration x=0.01, 0.04 and 0.10 were synthesized by a solid state reaction method using oxalate precursors. A sintering procedure was carried out in air at 500 and 900  ^°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray diffraction spectra reveal that the dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in Zn-Mn-O samples with manganese concentrations x=0.01 and 0.04 sintered at low temperature (500  ^°C). Saturation magnetization in the x=0.01 sample is found to be at . The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.     

Evidence for instability in charge ordering Nd0.5Sr0.5MnO3

The transport properties and magnetic phase transitions of charge ordering manganites Nd_0.5Sr_0.5MnO₃ have been investigated. From resistivity measurements, a continuous increase of resistivity upon the thermal cycling occurs at , and shows an instable behavior in the system. The experimental results of magnetization and electron-spin-resonance spectra indicate that the ferromagnetic phase and antiferromagnetic phase coexist in a broad temperature region. We think that the origin of the instability stems from an inhomogeneous strain yielded in the ferromagnetic interface, due to the competition among different phases.     

Room-temperature ferromagnetism in nanoparticles of superconducting materials

Nanoparticles of superconducting (YBCO) () exhibit ferromagnetism at room temperature while the bulk YBCO, obtained by heating the nanoparticles at high temperature (940 ^°C), shows a linear magnetization curve. Across the superconducting transition temperature, the magnetization curve changes from that of a soft ferromagnet to a superconductor. Furthermore, our experiments reveal that not only nanoparticles of metal oxides but also metal nitrides such as NbN () and δ-MoN () exhibit room-temperature ferromagnetism.     

Magnetic and structural behavior of double perovskite

We report synthesis and characterization of new Sr₂ZrMnO₆ manganite-like material. Samples were produced by the solid state reaction method with sinterization temperatures up to 1400 °C. X-ray diffraction experiments reveal that structure belongs to the perovskite system, space group . Lattice parameter was obtained by means of Rietveld-type refinement, through the GSAS code. Magnetic properties were studied by using an MPMS Quantum Design SQUID. From measurements of magnetization as a function of temperature, we determine the occurrence of a paramagnetic–antiferromagnetic transition with Néel temperature 50 K. Curie–Weiss fitting permitted to obtain the magnetic characteristic parameters. At temperature regimes below the Néel temperature, strong evidences of frustration and an irreversibility temperature between zero field cooling (ZFC) and field cooling (FC) measurements were observed. Curves of magnetization as a function of applied field were performed at . Results show a hysteretic feature for Sr₂ZrMnO₆ magnetic material. This response is attributed to formation of magnetic clusters as a consequence of cationic (magnetic and no magnetic) disorder along the double perovskite structure.     

Magnetization fluctuation analysis and superconducting parameters of , Sm, Gd, Dy, Ho, Yb) superconductor

In this work we report the analysis of magnetization experimental data of the , Sm, Gd, Dy, Ho, Yb) superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess ΔM(T) for different values of temperature in each one of the samples. We describe a procedure for extracting the penetration depth and the coherence length parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples of La_0.5RE_0.5BaCaCu₃O_7-δ by using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence–Doniach framework. These data allowed to determine the characteristic temperature value T^* (73, 58, 48, 57, 56, 71 K, for RE=Y, Sm, Gd, Dy, Ho, Yb, respectively) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of magnetization as a function of logarithm of applied field. We notice that the values for these superconducting parameters are in agreement with the reports for high temperature superconductors. The obtained value of superconducting volumetric fraction is compared with that obtained through the measure of the Meissner effect.     

Anisotropy of the magnetocaloric effect in DyNiAl

We present study of the anisotropic magnetocaloric effect in DyNiAl. This compound crystallizes in the hexagonal ZrNiAl-type structure, orders magnetically below and undergoes a further magnetic phase transition at . The Dy-moments are aligned ferromagnetically along the hexagonal c-axis below T_C, the additional antiferromagnetic component develops within the basal plane below T₁. The magnetocaloric effect was evaluated from the magnetization measurements with field applied along the c-axis and perpendicular to it. Our data reveal a strong anisotropy of the magnetocaloric effect. The large effect occurs for field applied along the c-axis whereas the entropy change is small for the perpendicular field direction.