Bastian Klemke

Magnetic study of M-type doped barium hexaferrite nanocrystalline particles

Co-Ti and Ru-Ti substituted barium ferrite nanocrystalline particles BaFe12−2xCoxTixO19 with (0≤x≤1) and BaFe12−2xRuxTixO19 with (0≤x≤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 showed some kind of a transition from insulator to perfect insulator around TM. 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...

Dipolar Antiferromagnetism and Quantum Criticality in LiErF4

Dropping a Dimension? In most magnetic materials, the exchange interaction causes the spins on the neighboring sites of a crystal lattice to align. In the absence of exchange interactions, dipolar interactions, which are highly orientation dependent, are also expected to be able to cause magnetism. Kraemer et al. (p. 1416) present evidence for antiferromagnetism in a dipolar-coupled material, LiErF4. Although a three-dimensional system, its critical behavior was more reminiscent of a two-dimensional material. Scattering experiments reveal that magnetic ordering can arise from dipolar interactions, not only from exchange. Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF4, establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field Hc|| = 4.0 ± 0.1 kilo-oersteds. We discovered non–mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h4 universality class; in accord with this, the quantum phase transition at Hc exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations.

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 Mn3+ ions dominates the magnetic symmetry at 10 K Gamma(2)) at the Er3+(4b) and the Mn3+ sites. Our findings highlight the fundamentally different roles that Mn3+, R3+(2a), and R3+(4b) magnetism play in establishing the magnetic phase diagram of the hexagonal RMnO3 system.

Magnetic structure and interactions in the quasi-one-dimensional antiferromagnet CaV 2 O 4

CaV2O4 is a spin-1 antiferromagnet, where the magnetic vanadium ions have an orbital degree of freedom and are arranged on quasi-one-dimensional zig-zag chains. The first- and second-neighbor vanadium separations are approximately equal suggesting frustrated antiferromagnetic exchange interactions. High-temperature susceptibility and single-crystal neutron diffraction measurements are used to deduce the dominant exchange paths and orbital configurations. The results suggest that at high temperatures CaV2O4 behaves as a Haldane chain, but at low temperatures, it is a spin-1 ladder. These two magnetic structures are explained by different orbital configurations and show how orbital ordering can drive a system from one exotic spin Hamiltonian to another.

Magnetic excitations in the S = 1 2 antiferromagnetic-ferromagnetic chain compound BaCu 2 V 2 O 8 at zero and finite temperature

Unlike most quantum systems which rapidly become incoherent as temperature is raised, strong correlations persist at elevated temperatures in

Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

S=1/2

Magnetic phase diagram of CePt3B1-xSix

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

Transferrin Decorated Thermoresponsive Nanogels as Magnetic Trap Devices for Circulating Tumor Cells

_2

Magnetoelectric properties in orthorhombic Nd1−xYxMnO3: Neutron diffraction experiments

V

Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point

_2