Short-range Ferromagnetic Clusters Research Articles

Spin-glass like features in cluster-glass compounds La1−δMn0.7Fe0.3O3

The static and dynamic features of magnetization are investigated using dc magnetization and ac susceptibility measurements on La1−δMn0.7Fe0.3O3 for δ = 0 and 0.13. The results indicate that short range ferromagnetic clusters coexist with the glassy magnetic state. The analysis on the frequency dependence of spin freezing temperature (Tf) using the Vogel–Fulcher law and the dynamical scaling behaviour near Tf indicates that the spin freezing temperature behaves like a spin-glass transition temperature for both the compounds. The cluster-glass states of both the compounds exhibit similar characteristic features.

Detailed neutron study of the crossover from long-range to short-range magnetic ordering in(Nd1−xTbx)0.55Sr0.45MnO3manganites

We have applied three complementary neutron techniques (neutron diffraction, neutron depolarization, and small-angle neutron scattering) to investigate the crossover from long-range to short-range magnetic ordering in ${({\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x})}_{0.55}{\mathrm{Sr}}_{0.45}\mathrm{Mn}{\mathrm{O}}_{3}$ manganite compounds. The obtained results indicate that the ground state at $T=1.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is a long-range C-type canted ferromagnetic state for $0\ensuremath{\leqslant}x(\mathrm{Tb})\ensuremath{\leqslant}0.5$ with ferromagnetic domains larger than several hundreds of nm that decrease as the Tb content increases. In the concentration range $0.5\ensuremath{\leqslant}x(\mathrm{Tb})\ensuremath{\leqslant}0.6$, the ferromagnetic domain size decreases below $\ensuremath{\sim}100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and these large ferromagnetic clusters coexist in this concentration range with smaller short-range ferromagnetic clusters (around one nanometer size). For $x(\mathrm{Tb})\ensuremath{\geqslant}0.6$, only short-range ferromagnetic and A-type and C-type antiferromagnetic clusters are present and their size is below $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The obtained results are discussed in the context of the global phase diagram recently discussed for ${\mathrm{RE}}_{0.55}{\mathrm{Sr}}_{0.45}\mathrm{Mn}{\mathrm{O}}_{3}$ and in the context of the quantum critical point features recently suggested in manganites.

Nuclear and magnetic structures and magnetic properties of synthetic brochantite, Cu4(OH)6SO4

Cu4(OH)6SO4 (1) and Cu4(OD)6SO4 (2) were obtained by hydrothermal syntheses from copper sulfate and sodium hydroxide in H2O and D2O, respectively. They crystallize in the monoclinic system, space group P2(1)/a (14), a = 13.1206(5), b = 9.8551(3), c = 6.0295(2) Angstroms, beta = 103.432(3) degrees, V = 758.3(1) Angstroms(3), Z = 4 and a = 13.1187(5), b = 9.8552(3), c = 6.0293(2) Angstroms, beta = 103.410(3) degrees, V = 758.3(1) Angstroms(3), Z = 4, respectively. They are iso-structural to the mineral brochantite and consist of double chains of edge-sharing copper octahedra that are connected to one another by corners to form corrugated planes along bc; these planes are in-turn bridged by the unprecedented mu7-sulfate tetrahedra to give a 3D-structure. All the hydrogen atoms were precisely located from refinement of the neutron powder diffraction data of the deuterated sample. Magnetic susceptibility data reveal a low-dimensional behavior at high temperature and the presence of both ferromagnetic and antiferromagnetic super-exchanges resulting in a 3D long-range antiferromagnetic ordering at 7.5 K accompanied by a small canting of the moments. The transition is confirmed by a lambda-peak in the specific heat. The magnetic structure at 1.4 K shows the moments are oriented perpendicular to the corrugated planes with alternation along +/-a for neighboring chains within the double chains. The enhanced incoherent scattering at low-angle suggests the existence of short-range ferromagnetic clusters.