[en] We have studied the magnetic and dynamical properties of spin-frustrated magnet Dy₂Ti_2−x Fe_xO₇ single crystals. Bulk magnetization data of the heavily Fe doped samples give a negative Curie–Weiss temperature, probably suggesting the existence of short-range antiferromagnetic interaction in Fe-doped samples. Dynamical analyses show that the doped system still freezes into an ice-like state but it is more dynamical than that in pure spin ice Dy₂Ti₂O₇. Furthermore, the dynamic freezing of the spins is suppressed to lower temperatures, which is caused by the Dy-Fe spin interactions and the altered crystalline electric field. It is also found that the coordination number of Fe decreases at high doping level (x=0.15), leading to the change of the spin state of Fe³⁺. - Highlights: • Doped system Dy₂Ti_2−xFe_xO₇ still freezes into an icelike state. • Doped system is more dynamical than that in pure spin ice Dy₂Ti₂O₇. • The dynamic freezing of the Dy³⁺ spins is suppressed to lower temperatures. • The spin configuration of Fe³⁺ becomes high-spin state at high doping level

[en] The magnetic order and dynamical properties of spin-frustrated magnet Dy_2−xYb_xTi₂O₇ single crystals have been studied by dc and ac susceptibility measurements. It is found that the substitution of the Dy³⁺ by the Yb³⁺ in Dy₂Ti₂O₇ relaxes ferromagnetic coupling. In low Yb³⁺ doping samples, a spin freezing peak at T_f (T_f<3 K) and a single-ion effect peak T_s associated with Dy³⁺ are observed. With increasing Yb³⁺ doping, a new peak marked by T^⁎ associated with Yb³⁺ appears. We suggest that T^⁎ originates from the thermally activated spin fluctuations of Yb³⁺. It is also found that the relaxation process for T_s becomes both thermally activated and quantum tunneled in x≥1.0 samples. The low-temperature dynamical behaviors of Dy_2−xYb_xTi₂O₇ are dominated by the Dy–Yb spin interactions and the altered crystalline electric field. Moreover, crystal field-phonon coupling may contribute to the spin dynamic properties. - Highlights: • With increasing Yb³⁺ doping, a new peak marked by T* associated with Yb³⁺ appears. • The relaxation process for T_s associated with Dy³⁺ becomes both thermally activated and quantum tunneled in x≥1.0 samples. • The low-temperature dynamical behavior is closely associated with the Dy–Yb spin interactions and the altered crystalline electric field

[en] The substitution of magnetic Fe²⁺ for nonmagnetic Cu⁺ in the Cu_1-xFe_xIr₂S₄ system causes drastic changes in electromagnetic behavior. For x = 0.01 and 0.025, the Peierls-like phase transition step ΔM in magnetization increases with x increasing, and an unexpected spin transition occurs at T^*∼120 K. This may be attributed to the spin-polarization of the Ir⁴⁺ ions by the Fe²⁺ ions. When x exceed 0.1, the Peierls-like phase transition is suppressed completely. The magnetic state for Fe doped samples transforms from ferromagnetic (FM) to paramagnetic (PM), and back to the FM state again with the increase of x. For the highly doped samples, the FM domains formed by Fe²⁺ ions result in another transition at T^**∼110 K and the cluster-spin glass transition.

[en] The resistivity and magnetism for the Cu_1-x-yAg_xIr₂S₄ (x = 0, y 0, 0.05, 0.1, 0.15; y = 0, x = 0, 0.05, 0.1, 0.15) system were investigated. A Peierls-like phase transition occurs at T_MI∼226 K for CuIr₂S₄. The transition is suppressed in the Cu_1-xAg_xIr₂S₄ system, which is attributed to that the substitution of Ag, with its larger radius, for Cu releases the pressure of Ir-Ir. The transition temperature T_MI increases slightly with vacancies increasing in the Cu_1-yIr₂S₄, which corresponds to the increase of pressure. Our explanation about the pressure release and increase can also be applied to clarifying the pressure effect which is still an open question. The magnetization rises at low temperatures below T_MI. We suggest that it is attributed to remnant localized electrons, which do not participate in the Peierls-like phase transition, accompanied by spin-dimerization in this system. By fitting the experimental curves, we find that about 0.7% of the Ir⁴⁺ ions do not participate in the Peierls-like transition. The contributions of Pauli paramagnetism, Landau diamagnetism, Larmor diamagnetism and Curie magnetism can be distinguished

[en] In this paper, we report unusual thermal hysteresis behaviour in half-doped manganites Nd_0.5Sr_0.5-xCa_xMnO₃ (0.0 ≤ x ≤ 0.50). For 0.05 ≤ x < 0.25 samples, the magnetization curves show a counterclockwise hysteresis loop. For 0.25 < x ≤ 0.40 samples, however, they exhibit a clockwise loop. The inverse hysteretic behaviour stems from the competition between two kinds of strain, namely, the compressive strain and the tensile strain. The former produces a counterclockwise thermal hysteresis while the latter leads to a clockwise one. In the meantime, a magnetic instability is observed and the strain relaxation should be the main reason for it

[en] The electrical and magnetic properties of Ln_0.4Ca_0.6MnO₃ compositions (Ln = La, Pr, Nd, Sm) have been investigated. The effect of < r_A> on the charge-ordering behavior of the manganites is considered to be profound. The charge-ordering temperature T_CO increases with decreasing < r_A>, the antiferromagnetic charge-ordering state transforms from long-range into local short-range ordering and the magnetic behaviors for Ln = La, Pr, Nd, Sm are all different. Through the M-T, M-H, and electron spin resonance measurements, it is found that the magnetization in M-T curves comes from the paramagnetic contribution of disordered Mn ions at the B-site and magnetic ions at the A-site. The rise of T_CO is attributed to the fact that e_g electrons are localized by decreasing < r_A>, and the different behavior of M-T curves below T_CO originates from the number of remaining spin disordered Mn ions after the formation of the charge-ordering phase in the manganites

[en] A comprehensive study of the difference between CaFe_1-xNi_xAsF and CaFe_1-xCo_xAsF systems has been carried out by measuring the efficient charge carrier concentration, the valence states and the superconducting phase diagram. It is found that at the same doping level, Ni doping introduces nearly twice the number of charge carriers as Co doping. However, x-ray absorption near-edge spectroscopy measurements reveal that the valence state of Fe in both systems is close to 2, indicating that there is no valence mismatch. We suggest that the charge carriers in CaFe_1-xM_xAsF (M=transition metal elements) are not induced by valence mismatch but come from the difference in the number of outer-shell electrons. We also suggest that with Ni and Co doping, the systems change from a multi-band material in the underdoped regions to a single-band state in the overdoped regions.

[en] We investigated the magnetic properties of a geometrically frustrated magnet of ZnFe₂O₄ nanoparticles by carrying out the comprehensive measurements of dc magnetization and ac susceptibility. Spin glass is confirmed to occur in this weakly Fe(Zn)-ionic-inversed sample. The common characteristics of spin glass including the aging, the memory, and the rejuvenation effects were observed. By using the critical-power law to study the spin dynamics, the spin-glass transition temperature T_g is obtained to be 18 K and the dynamic exponent zν is 8.0. The weak exchange interaction disorder introduced by the ferrimagnetic J_AB interaction, together with the weak nonmagnetic dilute disorder induced by the ionic inversion, is responsible for the formation of spin glass in the ZnFe₂O₄ nanoparticles.

[en] In this paper, the magnetocaloric effect of perovskite manganite Nd_0.6La_0.1Sr_0.3MnO₃ has been investigated. From the measurement of isothermal magnetization around the Curie temperature, we have calculated the maximum isothermal magnetic entropy change as 3.14 J/kg K for the 1.5 T magnetic field variation. Furthermore, a large relative cooling power of 45 J/kg has been determined, which makes Nd_0.6La_0.1Sr_0.3MnO₃ attractive candidate materials for magnetic refrigeration.

[en] The physical properties of itinerant ferromagnet -Co₅Ge₃ with both strong disorder and spin fluctuations was studied. The dc and ac susceptibility show that both spin fluctuations and disorder dominate the physical properties. In the spin glass phase, with a coexisting ferromagnetic state (30 K), both non-Fermi liquid behavior and large exponent of scaling relation of are observed and attributed to the spin fluctuations and disorder induced by cobalt defects. Upon the increase of external field, Fermi liquid behavior restores due to the suppression of spin fluctuations and disorder. In addition, a large anomalous Hall coefficient R _s is observed. Our results suggest that -Co₅Ge₃ is a typical itinerant ferromagnet to explore the interplay of disorder and spin fluctuations. (paper)