[en] Published in summary form only

[en] The temperature dependence of the AC susceptibility (χ) at constant applied magnetic field was investigated in the paramagnetic region close to the ferromagnetic transition in MnP. Above the curie temperature (T_c=291.9 K), a maximum in the χ(T,H) curves was observed at T_m(H). The temperature of the maximum increases with increasing the applied field. The behavior of T_m(H) is governed by the gap exponent of the scaling function (Δ=γ+β). From the fitting of our data we found that Δ=1.51±0.03 which is in excellent agreement with the theoretical predictions that are in the range 1.49<Δ<1.56

[en] The magnetic phase diagram of the nearly 2D ferromagnet (CH₃NH₃)₂CuCl₄ (T_C=8.85 K) in magnetic fields applied perpendicular to the easy axis is obtained. In this system, the ferromagnetic moments lie in planes (ab planes) formed by the Cu atoms and point along the a crystallographic direction. For field applied along b-axis (intermediate anisotropy axis), a second-order transition to the paramagnetic phase occurs at the field of 80 Oe at the lowest measured temperature (T=1.8 K). When the field is applied in a direction perpendicular to the Cu planes (c-axis) the paramagnetic phase is reached only above 1500 Oe after a double transition. The first transition (∼500 Oe) is suggested to be an order-order transition in which a spin reorientation occurs. The obtained in-plane and out-of-plane anisotropy are H_Aⁱⁿ=80 and H_A^out=1500 Oe, respectively

[en] Recent results from the experimental study of phase transitions in magnetic systems induced by a external magnetic field, mainly multicritical point which can occur in phase diagrams, are reviewed. (L.C.)

[en] From magnetization and ac susceptibility measurements we obtain the complete magnetic phase diagram of single crystals of Cs₂FeCl₅·H₂O for magnetic field up to 15 T. The magnetic field was applied along the directions parallel and perpendicular to the easy axis and the magnetization measured to temperatures down to 0.5 K. At zero magnetic field the antiferromagnetic ordering occurs at T_N=6.63 K. For the field applied parallel to the easy axis the antiferromagnetic (AF) to the spin-flop (SF) transition occurs for fields from 1.4 T to 1.1 T depending on the temperature. The low temperature transition from the (SF) to the paramagnetic (P) phase occurs at 13.15 T. In the perpendicular configuration this transition occurs at fields around 13.5 T. From the extrapolation of the transition fields to zero temperature, we obtain a ratio of the anisotropy field H_A to exchange field H_E, α=H_A/H_E=(1.4±0.2)×10⁻². A comparison with the phase diagram measured for MnF₂ is included. - Highlights: • Complete phase diagram of Cs₂FeCl₅·H₂O for magnetic fields up to 15 T. • Direct determination of the anisotropy ratio=HA/HE. • Partial phase diagram of the diluted sample. • Estimative of the high field transition value for MnF₂

[en] We report on the magnetic effects induced by the substitution of Mn²⁺ by Cu²⁺ ions in the quasi-one-dimensional Heisenberg-like antiferromagnet CsMnA₃·2H₂O (A=Cl, Br). In the diluted samples of the Br derivative we observe the appearance of a remanent magnetization below T_N when they are cooled in a small axial field applied along the easy axis. This does not occur in the diluted samples of the Cl derivative. The intra-chain exchange both in Cl and Br compounds is antiferromagnetic, however the inter-chain exchange along the easy axis is antiferromagnetic in the chloride compound and ferromagnetic in the bromide. This fact seems to be deterministic in the appearance of the net moments below T_N in the bromine

[en] Published in summary form only

No abstract available

[en] Magnetization measurements on single crystals of the site-diluted antiferromagnet A₂Fe_1-xIn_xCl₅·H₂O (A=Cs) were carried out at low magnetic fields (H) applied along the easy axis. The data revealed that a remanent magnetization M_r develops below the Neel temperature T_N. This M_r (T) is parallel to the easy axis, saturates for H∼1 Oe and it increases with decreasing T. It has also the same temperature dependence as other diluted systems of the same family (A=K, Rb). For all these systems the normalized M_r(t)/M_r(t=0.3), where t=T/T_N is the reduced temperature, is independent of x and follows a universal curve

[en] The magnetic excitation spectra of the low anisotropy Heisenberg antiferromagnetic S=((5)/(2)) systems K₂Fe_1-xIn_xCl₅·D₂O (x=0.0 and 0.05) are studied by means of inelastic neutron scattering experiments. A set of four exchange constants and the anisotropy energy have been determined from the analysis of the dispersion curves using a four-sublattice model. No indication of magnon-fracton crossover is observed from our results