0000000000765214
AUTHOR
G. Allodi
Magnetic order, metamagnetic transitions, and low-temperature spin freezing in Ca3Co2O6: an NMR study
We report on a 59Co NMR investigation of the trigonal cobaltate Ca3Co2O6 carried out on a single crystal, providing precise determinations of the electric field gradient and chemical shift tensors, and of the internal magnetic fields at the non-magnetic Co I sites, unavailable from former studies on powders. The magnetic field-induced ferri- and ferromagnetic phases at intermediate temperature (e.g. 10 K) are identified by distinct internal fields, well accounted for by purely dipolar interactions. The vanishing transferred hyperfine field at the Co I site indicates that the Co3+(I) orbitals do not participate in the intra-chain superexchange, in disagreement with a previous theoretical mod…
Magnetic phase diagram of La$_{2-x}$Sr$_{x}$CoO$_{4}$ revised using muon-spin relaxation
We report the results of a muon-spin relaxation ($\mu$SR) investigation of La$_{2-x}$Sr$_{x}$CoO$_{4}$, an antiferromagnetic insulating series which has been shown to support charge ordered and magnetic stripe phases and an hourglass magnetic excitation spectrum. We present a revised magnetic phase diagram, which shows that the suppression of the magnetic ordering temperature is highly sensitive to small concentrations of holes. Distinct behavior within an intermediate $x$ range ($0.2 \leq x \lesssim 0.6$) suggests that the putative stripe ordered phase extends to lower $x$ than previously thought. Further charge doping ($0.67 \leq x \leq 0.9$) prevents magnetic ordering for $T \gtrsim 1.5~…
Band filling effect on polaron localization in La$_{1-x}($Ca$_y$Sr$_{1-y}$)$_{x}$MnO$_3$ manganites
We report on an a $\mu$SR and $^{55}$Mn NMR investigation of the magnetic order parameter as a function of temperature in the optimally doped La$_{5/8}$(Ca$_y$Sr$_{1-y}$)$_{3/8}$MnO$_3$ and in the underdoped La$_{1-x}$Sr$_{x}$MnO$_3$ and La$_{1-x}$Ca$_{x}$MnO$_3$ metallic manganite families. The study is aimed at unraveling the effect of lattice distortions, implicitly controlled by the Ca-Sr isoelectronic substitution, from that of hole doping $x$ on the Curie temperature $T_c$ and the order of the magnetic transition. At optimal doping, the transitions are second order at all $y$ values, including the $y=1$ (La$_{5/8}$Ca$_{3/8}$MnO$_3$) end member. In contrast, they are first order in the…