Field Induced Magnetic Ordering and Single-ion Anisotropy in the Quasi-1D Haldane Chain Compound SrNi2V2O8: A Single Crystal investigation

Field-induced magnetic ordering in the Haldane chain compound SrNi$_{2}$V$_{2}$O$_{8}$ and effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-field magnetization, and low temperature heat-capacity studies confirm a non-magnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intra-chain exchange interaction is estimated to be $J \sim 8.9{\pm}$0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropy $D(S^z){^2}$. The value of {\it D} is estimated to be $-0.51{\pm}0.01$ meV and the easy axis is found to be along the crystallographic {\it c}-axis. Field-induced magnetic ordering has been found with two critical fields [$\mu_0H_c^{\perp c} = 12.0{\pm}$0.2 T and $\mu_0H_c^{\parallel c} = 20.8{\pm}$0.5 T at 4.2 K]. Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-field magnetization study. The Phase diagram in the {\it H-T} plane has been obtained from the high-field magnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds

Kondo lattice heavy fermion behavior in CeRh2Ga2

The physical properties of an intermetallic compound CeRh2Ga2 have been investigated by magnetic susceptibility \chi(T), isothermal magnetization M(H), heat capacity C_p(T), electrical resistivity \rho(T), thermal conductivity \kappa(T) and thermopower S(T) measurements. CeRh2Ga2 is found to crystallize with CaBe2Ge2-type primitive tetragonal structure (space group P4/nmm). No evidence of long range magnetic order is seen down to 1.8 K. The \chi(T) data show paramagnetic behavior with an effective moment \mu_eff ~ 2.5 \mu_B/Ce indicating Ce^3+ valence state of Ce ions. The \rho(T) data exhibit Kondo lattice behavior with a metallic ground state. The low-T C_p(T) data yield an enhanced Sommerfeld coefficient \gamma = 130(2) mJ/mol K^2 characterizing CeRh2Ga2 as a moderate heavy fermion system. The high-T C_p(T) and \rho(T) show an anomaly near 255 K, reflecting a phase transition. The \kappa(T) suggests phonon dominated thermal transport with considerably higher values of Lorenz number L(T) compared to the theoretical Sommerfeld value L_0.Comment: 6 pages, 6 figures, 1 table, Accepted for publication in J. Phys.: Condens. Matte

Magnetic excitations in the S = 1/2 antiferromagnetic-ferromagnetic chain compound BaCu2V2O8 at zero and finite temperature

Unlike most quantum systems which rapidly become incoherent as temperature is raised, strong correlations persist at elevated temperatures in $S=1/2$ dimer magnets, as revealed by the unusual asymmetric lineshape of their excitations at finite temperatures. Here we quantitatively explore and parameterize the strongly correlated magnetic excitations at finite temperatures using the high resolution inelastic neutron scattering on the model compound BaCu$_2$V$_2$O$_8$ which we show to be an alternating antiferromagnetic-ferromagnetic spin$-1/2$ chain. Comparison to state of the art computational techniques shows excellent agreement over a wide temperature range. Our findings hence demonstrate the possibility to quantitatively predict coherent behavior at elevated temperatures in quantum magnets.Comment: 5 pages + 6 pages supplement; problems with list of references are fixe

An ultra-low field SQUID magnetometer for measuring antiferromagnetic and weakly remanent magnetic materials at low temperatures

A novel setup for the measurement of magnetic fields external to certain antiferromagnets and generally weakly remanent magnetic materials is presented. The setup features a highly sensitive Super Conducting Quantum Interference Device (SQUID) magnetometer with a magnetic field resolution of approx. 10 fT, non-electric thermalization of the sample space for a temperature range of 1.5 - 65 K with a non-electric sample movement drive and optical position encoding. To minimize magnetic susceptibility effects, the setup components are degaussed and realized with plastic materials in sample proximity. Running the setup in magnetically shielded rooms allows for a well-defined ultra low magnetic background field well below 150 nT in situ. The setup enables studies of inherently weak magnetic materials which cannot be measured with high field susceptibility setups, optical methods or neutron scattering techniques, giving new opportunities for the research on e.g. spin-spiral multiferroics, skyrmion materials and spin ices

Mutual induction of magnetic 3d and 4f order in multiferroic hexagonal ErMnO3

The complex interplay between the 3d and 4f moments in hexagonal ErMnO3 is investigated by magnetization, optical second harmonic generation, and neutron-diffraction measurements. We revise the phase diagram and provide a microscopic model for the emergent spin structures with a special focus on the intermediary phase transitions. Our measurements reveal that the 3d exchange between Mn^{3+} ions dominates the magnetic symmetry at 10 K < T < T_N with Mn^3+ order according to the Gamma_4 representation triggering 4f ordering according to the same representation on the Er^{3+}(4b) site. Below 10 K the magnetic order is governed by 4f exchange interactions of Er^{3+} ions on the 2a site. The magnetic Er^{3+}(2a) order according to the representation Gamma_2 induces a magnetic reorientation (Gamma_4 --> Gamma_2) at the Er^{3+}(4b) and the Mn^{3+} sites. Our findings highlight the fundamentally different roles the Mn^{3+}, R^{3+}(2a), and R^{3+}(4b) magnetism play in establishing the magnetic phase diagram of the hexagonal RMnO3 system

Magnetic study of M type doped barium hexaferrite nanocrystalline particles

Co Ti and Ru Ti substituted barium ferrite nanocrystalline particles BaFe12 2xCoxTixO19 with 0 lt;x lt;1 and BaFe12 2xRuxTixO19 with 0 lt;x lt;0.6 were prepared by ball milling method, and their magnetic properties and their temperature dependencies were studied. The zero field cooled ZFC and field cooled FC processes were recorded at low magnetic fields and the ZFC curves displayed a broad peak at a temperature TM. In all samples under investigation, a clear irreversibility between the ZFC and FC curves was observed below room temperature, and this irreversibility disappeared above room temperature. These results were discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The resistivity data show some kind of a transition from insulator to perfect insulator around . At 2 K, the saturation magnetization slightly decreased and the coercivity dropped dramatically with increasing the Co Ti concentration x. With Ru Ti substitution, the saturation magnetization showed small variations, while the coercivity decreased monotonically, recording a reduction of about 73 at x 0.6. These results were discussed in light of the single ion anisotropy model and the cationic distributions based on previously reported neutron diffraction data for the CoTi substituted system, and the results of our Mössbauer spectroscopy data for the RuTi substituted system

Low Temperature Properties of Selected Kramers Rare Earth Oxychlorides

In this work, we present low temperature magnetic and electronic properties measured on selected Kramers rare earth oxychlorides REOCl, RE Nd, Gd, Dy which adopt the PbFCl type of structure. Prepared powder samples were characterized by means of standard structural, magnetic and electronic methods as X ray diffraction 300 K , heat capacity 0.3 K 12 K and susceptibility measurements 2 K 300 K, at ambient pressure and hydrostatic pressures up to 0.68 0.01 GPa . Our results indicate new transition to the ordered magnetic state for GdOCl and NdOCl compound at temperatures of 5 K and 1.5 K, respectively. We found small increase of magnetization saturation value of dysprosium oxychloride with an applied hydrostatic pressure, but no remarkable changes occur to antiferromagnetic transition temperature TN 9.2 K when a moderate hydrostatic pressure p 0.68 0.01 GPa was applied. Observed deviations from the CurieWeiss behavior below 26 K can be caused by the vicinity of the magnetic ordering temperature, or another magnetic effects. The single crystal experiments which will solve this opened question are in progres

Ultralight magnetic aerogels from Janus emulsions

Magnetite containing aerogels were synthesized by freeze drying olive oil silicone oil based Janus emulsion gels containing gelatin and sodium carboxymethylcellulose NaCMC . The magnetite nanoparticles dispersed in olive oil are processed into the gel and remain in the macroporous aerogel after removing the oil components. The coexistence of macropores from the Janus droplets and mesopores from freeze drying of the hydrogels in combination with the magnetic properties offer a special hierarchical pore structure, which is of relevance for smart supercapacitors, biosensors, and spilled oil sorption and separation. The morphology of the final structure was investigated in dependence on initial compositions. More hydrophobic aerogels with magnetic responsiveness were synthesized by bisacrylamide crosslinking of the hydrogel. The crosslinked aerogels can be successfully used in magnetically responsive clean up experiments of the cationic dye methylene blue

FOXP3+CD25− Tumor Cells with Regulatory Function in Sézary Syndrome

Cutaneous T-cell lymphoma (CTCL) has been suggested by in vitro experiments to represent a malignant CD4+ T-cell proliferation with a regulatory T-cell (Treg) phenotype (CD4+CD25+FOXP3+). We investigated percentages of FOXP3+ and CD25+ cells in the blood of 15 Sézary, 14 mycosis fungoides (MF), and 10 psoriasis (Pso) patients and 20 normal healthy donors (NHDs). We found similar numbers of FOXP3+ cells in MF (10.4% of blood CD4+ cells) and Pso (11.1%) patients and NHDs (9.8%). In 8 of 15 (53%) Sézary patients, significantly reduced percentages of FOXP3+ cells were seen in blood (2.9%) and skin (10.4%). Interestingly, 6 of 15 (40%) Sézary patients showed significantly increased percentages of FOXP3+ cells (39.7% (blood), 20.3% (skin)); however, these cells did not express CD25. In these latter patients, clone-specific TCR-Vβ-chain antibodies were used to demonstrate that these FOXP3+CD25− cells were monoclonal CTCL tumor cells. FOXP3+CD25− CTCL tumor cells showed a highly demethylated status of the foxp3 gene locus similar to Treg cells, and they were functionally able to suppress IL-2 mRNA induction in TCR-stimulated conventional T cells. Thus, FOXP3+CD25− CTCL tumor cells with functional features of Treg cells define a subgroup of Sézary patients who might carry a different prognosis and might require differential treatment