Magnetic Spin Reorientation Transition Research Articles

Magnetocaloric properties and hysteresis loops of hexagons in a square–hexagon-octagon (4-6-8) structure with mixed spins: Monte Carlo study

In this work, we have studied the magnetocaloric properties of a 1, 3/2 and 5/2 mixed spin model on a square–hexagon-octagon (4-6-8) structure, investigated by Monte Carlo simulations. The total magnetization and the magnetization of each sub-lattice of the mixed-spin lattice have been analyzed. We investigated the effects of the external magnetic field, the exchange coupling interactions and the temperature in order to explicit the magnetic properties of these structure systems. The magnetic susceptibility and heat specific were determined. The magnetic spin-reorientation transition and ferrimagnetic-paramagnetic transitions were found, along with the magnetic entropy changes. Finally, the hysteresis loops under the effect of exchange interactions, temperatures and the crystal fields have been discussed.

The magnetic spin-reorientation transitions in the RGa (R=rare earth) intermetallic compounds studied by measurements of the hyperfine interactions of the 119Sn probe atoms

The magnetic and electric hyperfine interactions of the probe nucleus 119Sn on the Ga site of the ferromagnetic rare-earth (R) gallium compounds RGa (R=Pr–Er) have been investigated by Mössbauer spectroscopy technique. For all of the compounds, the directions of the magnetic moments of the R 3+ ions have been determined as a function of temperature in the range from 5 K to T C. For NdGa, SmGa, HoGa, and ErGa compounds, the magnetic reorientation transitions due to the competition between the exchange interaction and the interaction with crystal field have been investigated. At high temperatures, when the electric interaction dominates, the orientation of the magnetic moments is unambiguously determined by the sign of the quadrupole moment of 4f shell of the R 3+ ion. With decreasing temperature, the magnetic moments rotate gradually from the bc-plane toward the crystallographic a-axis. In the temperature range 5 K⩽ T<100 K, the ferromagnetic structure of the GdGa compound is noncollinear. At 5 K the magnetic moments of the Gd 3+ ions point in two distinct directions with respect to the crystallographic a-axis ( θ 1 ≈ 30 ° and θ 2 ≈ 60 ° ).

Reversible effect of hydrogen on superconductivity and weak ferromagnetism inEu1.4Ce0.6MSr2Cu2O10−δ(M=Nband Ru)

We have investigated the superconducting compounds ${\mathrm{Eu}}_{1.4}{\mathrm{Ce}}_{0.6}M{\mathrm{Sr}}_{2}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ ($M=\mathrm{Nb}$ and Ru) (${T}_{c}=22$ and 32 K, respectively), as well as these materials charged with hydrogen, by several complementary experimental techniques. ${\mathrm{Eu}}_{1.4}{\mathrm{Ce}}_{0.6}{\mathrm{RuSr}}_{2}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ is magnetically ordered at ${T}_{N}=122\mathrm{K},$ thus ${T}_{N}\ensuremath{\gg}{T}_{c}.$ Superconductivity (SC) is confined to the ${\mathrm{CuO}}_{2}$ planes, and the magnetic ordering is due to the Ru sublattice. Among many interesting features, irreversibility phenomena at low magnetic fields and a magnetic spin reorientation transition, which are observed, originate from antisymmetric exchange coupling of the Dzyaloshinsky-Moria type. The effect of hydrogen (0.35 at. %) is to suppress SC in both compounds and to enhance the weak-ferromagnetic properties of the Ru sublattice ${(T}_{N}=225\mathrm{K}).$ In contrast to other high-${T}_{c}$ materials, this effect is reversible: namely, by depletion of hydrogen, SC is restored in both materials and for $M=\mathrm{Ru},$ the ${T}_{N}$ drops back to 122 K.