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The magnetic ordering of four Tb3+-doped manganites and cobaltites, La0.7Tb0.1Sr0.2MnO3, La0.7Tb0.1Ca0.2MnO3, La0.7Tb0.1Sr0.2CoO3 and La0.7Tb0.1Ca0.2CoO3, have been studied by means of neutron diffraction and SQUID magnetometry. All the samples were prepared by sintering of sol-gel precursors and their orthorhombic or rhombohedral perovskite structures at room and low temperatures were refined. A long-range ferromagnetic (FM) order was detected at the Mn and Co sites. In addition, a small but significant ordered moment was observed at A sites of studied cobaltites, which was attributed to local Tb3+ moments, aligned by exchange interactions due to FM ordered Co sublattice. No or minor Tb3+ contribution was detected in studied manganites.

Rare-earth-doped ferromagnetic manganites La0.63RE0.07Sr0.30MnO3 (RE = Gd, Tb, Dy, and Ho) are synthesized in the form of sintered ceramics and nanocrystalline phases with the mean size of crystallites ≈30 nm. The electronic states of the dopants are investigated by SQUID magnetometry and theoretically interpreted based on the calculations of the crystal field splitting of rare-earth energy levels. The samples show the orthorhombic perovskite structure of Ibmm symmetry, with a complete FM order of Mn spins in bulk and reduced order in nanoparticles. Non-zero moments are also detected at the perovskite A sites, which can be attributed to magnetic polarization of the rare-earth dopants. The measurements in external field up to 70 kOe show a standard Curie-type contribution of the spin-only moments of Gd3+ ions, whereas Kramers ions Dy3+ and non-Kramers ions Ho3+ contribute by Ising moments due to their doublet ground states. The behaviour of non-Kramers ions Tb3+ is anomalous, pointing to singlet ground state with giant Van Vleck paramagnetism. The Tb3+ doping leads also to a notably increased coercivity compared to other La0.63RE0.07Sr0.30MnO3 systems.

Three forms of La,Sr-manganites are synthesized and the role of Tb doping is investigated. First two systems are sol-gel nanoparticles and sintered ceramics of the composition La0.56Tb0.07Sr0.37MnO3, whereas the third system is formed by comparable nanoparticles La0.51Tb0.06Sr0.43MnO3 synthesized in molten salt. The samples show pseudocubic perovskite structure with only small tilts of MnO6 that point to Ibmm symmetry in the bulk and [Formula: see text] symmetry in nanoparticles. SQUID magnetometry and neutron diffraction reveal a complete FM order of Mn spins in bulk, a reduced order in nanoparticles, and non-zero moments at A sites. Detailed analysis suggests that the dodecahedral coordination of A sites adapts to small terbium size, and the resulting crystal field splitting of Tb(3+) yields a singlet ground state. The response to exchange and external fields is characterized as a giant Van Vleck paramagnetism in contrast to the Curie-type behaviour of Tb-based orthoaluminates and orthocobaltites with the quasi-doublet ground state.

This study is aimed at the preparation of silica-coated nanoparticles of cobalt–zinc ferrite and their heating properties with respect to potential application in magnetic fluid hyperthermia. The magnetic cores of Co0.4Zn0.6Fe2O4+γ possessing two different sizes were prepared by the coprecipitation method followed by annealing and mechanical treatment. The subsequent encapsulation of the samples by silica led to colloidally stable suspensions in water. The single phase character of the cores was confirmed by x-ray powder diffraction while detailed studies of the coated products by transmission electron microscopy and x-ray photoelectron spectroscopy showed that the silica shell had a thickness of at least 5 nm. The dc magnetic measurements were employed in order to determine the concentrations of magnetic particles in suspensions and to analyse the distribution of blocking temperatures. The heating efficiency of the nanoparticles was studied simultaneously by means of magnetic and calorimetric measurements in various ac fields. Specifically, the magnetic losses were calculated from the ac hysteresis loops while the heating effect of the nanoparticles was determined by measuring the time dependence of the temperature of their suspensions. The evaluation of the heating power from the latter experiments was supplemented by deriving the corrections for non-adiabatic properties of the calorimeter. More accurate results enabled detailed analysis and comparison with data published for other heating agents.

Dielectric properties of Eu(0.5)Ba(0.5)TiO(3) ceramics were investigated between 10 and 300 K in the frequency range of 1 MHz-100 THz. Permittivity exhibits a strong peak near the ferroelectric phase transition at 215 K. This is mainly due to softening of the lowest frequency polar phonon revealed in THz and infrared spectra. Dielectric relaxation was observed also below the ferroelectric soft mode frequency in the whole investigated temperature region, but it is probably caused by some defects such as Eu(3 + ) cations or oxygen vacancies. This implies that the ferroelectric phase transition has predominantly a displacive character. Raman scattering spectra revealed a lowering of crystal symmetry in the ferroelectric phase and XRD analysis indicated orthorhombic A2mm symmetry below 215 K. The magnetic measurements performed at various frequencies in the field cooled and field heating regime after cooling in zero magnetic fields excluded spin glass behavior and proved an antiferromagnetic order below 1.9 K in Eu(0.5)Ba(0.5)TiO(3).

The as-prepared and heat treated iron/cobalt nanoparticles with r = Co/Fe = 0.08 and 1 were obtained by laser decomposition. At low temperatures all the materials are in a ferromagnetic blocked state. At higher temperatures (T > 200 K) the as-prepared materials exhibit superparamagnetic properties. In this case the nanoparticle size distribution deduced from the m(H) curves and from the difference between the FC and ZFC susceptibilities was compared with the TEM data. The heat treated materials have larger magnetizations and a maximum (161 emu/g) was achieved for the r = 1 material heat treated at 900?. For this material an anomalous form of the hysteresis loop was explained in terms of a superposition of single and multi-domain magnetizations.