[en] Highlights: • EuRu2P2 is a ferromagnet with a small anisotropy with a as an easy magnetization axis. • The magnetocrystalline anisotropy was confirmed by ab-initio calculations. • Full saturated magnetic moment confirms the Eu2 + state over all pressures. • Sudden drop of Tc at 1.5 GPa is ascribed to the lattice compressibility change. -- Abstract: The EuRu₂P₂ single crystal was investigated by means of magnetic, transport and thermodynamic studies at ambient and hydrostatic pressures. A small magnetocrystalline anisotropy with crystallographic [100] direction as an easy magnetization direction was found by experimental measurements and confirmed by first-principles calculations. We connect a previously reported change in the compressibility observed at room temperature to a rapid change of ordering temperature under applied hydrostatic pressure.

[en] We report on detailed low-temperature measurements of the magnetization, the specific heat and the electrical resistivity on high-quality CeRuSn single crystals. The compound orders antiferromagnetically at T_N = 2.8 K with the Ce³⁺ ions locked within the a–c plane of the monoclinic structure. Magnetization shows that below T_N CeRuSn undergoes a metamagnetic transition when applying a magnetic field of 1.5 and 0.8 T along the a- and c-axis, respectively. This transition manifests in a tremendous negative jump of ∼25% in the magnetoresistance. The value of the saturated magnetization along the easy magnetization direction (c-axis) and the magnetic entropy above T_N derived from specific heat data correspond to the scenario of only one third of the Ce ions in the compound being trivalent and carrying a stable Ce³⁺ magnetic moment, whereas the other two thirds of the Ce ions are in a nonmagnetic tetravalent and/or mixed valence state. This is consistent with the low-temperature CeRuSn crystal structure i.e., a superstructure consisting of three unit cells of the CeCoAl type piled up along the c-axis, and in which the Ce³⁺ ions are characterized by large distances from the Ru ligands while the Ce–Ru distances of the other Ce ions are much shorter causing a strong 4f-ligand hybridization and hence leading to tetravalent and/or mixed valence Ce ions. (paper)

[en] There is an ongoing dispute in the community about the absence of a magnetic quantum critical point (QCP) in the noncentrosymmetric heavy fermion compound CeRhSi₃. In order to explore this question we prepared single crystals of CeRh(Si_1−xGe_x)₃ with x = 0.05 and 0.15 and determined the temperature–pressure (T–p) phase diagram by means of measurements of the electrical resistivity. The substitution of isoelectronic but large Ge enforces a lattice volume increase resulting in a weakening of the Kondo interaction. As a result, the x = 0.05 and x = 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures being T _N = 4.7 K and T _N1 = 19.7 K, respectively. Application of pressure suppresses T _N (T _N1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds above p ⩾ 2.16 GPa (x = 0.05) and p ⩾ 2.93 GPa (x = 0.15). Extrapolation of T _N(p) → 0 of CeRh(Si_0.95Ge_0.05)₃ yields a critical pressure of p _c ≈ 3.4 GPa (in CeRh(Si_0.85Ge_0.15)₃  p _c ≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state. (paper)

[en] Dielectric response of perovskite Sr_1_−_xBa_xMnO_3 (x  =  0.43 and 0.45) ceramics was investigated using microwave, THz and infrared spectroscopic techniques in order to study the ferroelectric and antiferromagnetic phase transitions with critical temperatures T _C  ≈  350 K and T _N  ≈  200 K, respectively. The two lowest-frequency polar phonons are overdamped above T _N and they exhibit pronounced softening on heating towards T _C. Nevertheless, permittivity ε′ in the THz range shows only a small anomaly at T _C because the phonon contribution to ε′ is rather small. The phonons are coupled with a central mode which provides the main contribution to the dielectric anomaly at T _C. Thus, the ferroelectric phase transition has characteristics of a crossover from displacive to order–disorder type. At the same time, the intrinsic THz central peak is partially screened by conductivity and related Maxwell–Wagner relaxation, which dominates the microwave and lower-frequency spectra. Below T _N, the ferroelectric distortion markedly decreases, which has an influence on the frequencies of both the central and soft modes. Therefore, ε′ in the THz range increases at T _N on cooling. In spite of the strong spin–phonon coupling near T _N, surprisingly no magnetodielectric effect was observed in the THz spectra upon applying magnetic field of up to 7 T, which is in contradiction with the theoretically expected huge magnetoelectric coupling. We explain this fact as due to the insensitivity of T _N to magnetic field. (paper)

[en] Highlights: • Thermal expansion of Ce₂Pd₂In is anisotropic having opposite sign along a or c. • Ce magnetic moments and long-range order are remarkably stable in applied pressures. • Hydrostatic pressure promotes antiferromagnetism on the account of ferromagnetism. • Uniaxial pressure along c-axis has no significant effect on transition temperatures. • Two types of magnetic order in Ce₂Pd₂In are effectively degenerate. -- Abstract: Among a large group of R₂T₂X intermetallics (R = rare earth, T = transition element, X = p-metal) crystallizing in the Shastry-Sutherland-like tetragonal structure, Ce₂Pd₂In represents a rare example of Ce-based ferromagnet, reached, however via an antiferromagnetic phase stable at higher temperatures. Here we describe the development of magnetism in Ce₂Pd₂In under external hydrostatic and uniaxial pressure, monitored by means of electrical resistivity, magnetization, and AC magnetic susceptibility experiments on a high-quality single crystal. The experiments prove a stability of the 4f magnetism in pressures up to 3 GPa. At these pressures only slightly reduced spontaneous magnetization in the FM state and enhanced electrical resistivity with signs of Kondo lattice behavior are observed. The AFM Néel temperature (T_N = 4.65 K) is essentially pressure independent, while the Curie temperature (T_C = 4.16 K at ambient pressure) significantly decreases under hydrostatic pressure. The fact that the ferromagnetic phase can be re-entered in weak magnetic fields (0.05 T) proves that the two types of magnetic order are effectively degenerate. Interestingly, T_C is not affected by uniaxial pressure applied along the tetragonal c-axis, T_N value exhibits only a weak decrease of 0.25 K GPa⁻¹ under such uniaxial pressure. The crystal structure of Ce₂Pd₂In exhibits a strongly anisotropic thermal expansion with anomalous expansion of the c-parameter with decreasing T. Modest size of magnetostriction effects, observed by dilatometry at ambient pressure, indicates only regular magnetovolume interactions.

[en] We report on the specific heat, magnetization and ac susceptibility measurements of single crystals of hybrid frustrated magnets Gd_1.8Tb_0.2Ti₂O₇ and Gd_1.5Tb_0.5Ti₂O₇. The analysis of experimental data revealed that, although partial replacing of the Gd³⁺ ions by the Tb³⁺ ions in the Gd₂Ti₂O₇ host lattice slightly enhances antiferromagnetic coupling, as inferred from the evolution of the paramagnetic Curie-Weiss temperature, the ordering temperature gradually decreases. Paramagnetic correlations introduced by the Tb³⁺ ions cause this perturbation, altering the effective further neighbor interactions and destabilizing the ground state in Gd₂Ti₂O₇. In addition, the low-energy states of Gd_2-xTb_xTi₂O₇ are suggested to possess a nature different from those in parent members Tb₂Ti₂O₇ and Gd₂Ti₂O₇. Finally, the frequency-dependent magnetic susceptibility behavior in Gd_1.5Tb_0.5Ti₂O₇ is consistent with the formation of a spin-glass-like state indicating a pronounced slowing down of the dynamical response of the studied hybrid magnets. (paper)

[en] Polycrystalline YbAu_2Si_2 has been prepared by arc melting and a non-standard anisotropic thermal expansion is observed at low temperatures. A non-magnetic Yb"2"+ valence state is derived from magnetization, magnetic-susceptibility, heat-capacity and electrical-conductivity measurements in the temperature range from 0.3 to 300 K and at external pressures up to 3.2 GPa. By both experimental and theoretical investigations, YbAu_2Si_2 is confirmed to be a system with a weak electron-electron correlations and a small electron-phonon interaction. Application of hydrostatic pressure does not reveal any change of state in the range of applied pressures.

[en] We report the single crystal properties of CePd₂Zn₃ and CePd₂Ga₃ compounds. The compounds were prepared by Bridgman method in high-frequency induction furnace. Both compounds adopt the hexagonal PrNi₂Al₃-type structure with a = 5.3914(2) Å, c = 4.3012(2) Å for CePd₂Zn₃ and a = 5.4106(8) Å, c = 4.2671(8) Å for CePd₂Ga₃, respectively. CePd₂Zn₃ orders antiferromagnetically below T ${}_{\mathrm{N}}$ = 1.9 K. Magnetoresistance measurements revealed a crossover at B ${}_{\mathrm{c}}$ = 0.95 T. CePd₂Ga₃ orders ferromagnetically at T ${}_{\mathrm{C}}$ = 6.7 K. Applied hydrostatic pressure reduces the value of the Curie-temperature (rate $\partial T_{\mathrm{C}}/\partial p=0.9$ K GPa ${}^{-1}$) down to 3.9 K at 3.2 GPa. Both compounds display a strong magnetocrystalline anisotropy with easy axis of magnetization perpendicular to the c-axis in the hexagonal lattice.

[en] We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(H₂O)₄(CN)₆]⋅3H₂O (bpdo=4, 4′-bipyridine-N,N′-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S = 1/2 and a weak exchange interaction J/k_B = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd³⁺ ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field. (paper)

[en] Highlights: • We have studied structural and magnetic properties of TbNiAl single crystal. • We have studied properties of TbNiAl under uniaxial and hydrostatic pressure. • The uniaxial pressure (along c-axis) leads towards the ferromagnetic order. -- Abstract: We have studied development of structural and magnetic properties of TbNiAl single crystal under applied hydrostatic and uniaxial pressure. TbNiAl crystallizes in the hexagonal ZrNiAl-type structure. The lattice parameters show a transition between two phases with different c/a ratio around 120 K as evidenced by X-ray diffraction, resistivity and thermal expansion measurements. The application of hydrostatic pressure stabilizes the low c/a phase. The transition shifts consequently to lower temperatures with applied pressure and vanishes for pressure above 0.55 GPa. The magnetic properties are characterized by antiferromagnetic order below T_N = 45 K. The application of magnetic field of 0.3 T along the c-axis leads to a metamagnetic transition to ferromagnetic order. The critical field of this transition shifts considerably to higher values with hydrostatic pressure whereas the uniaxial pressure applied along the c axis moves the transition to lower fields. TbNiAl represents thus a rare example of a well localized system where the magnetic ground state is strongly influenced by external pressure. This behavior is discussed in connection with the structural parameters