Phase diagram for Ca_{1-x}Y_xMnO_3 type crystals

Alternating current susceptibility and direct current magnetization have been studied for polycrystalline Ca$_{1-x}$Mn$_x$O. On increasing the Mn content, magnetic ordering changes from spin-glass behavior for $0.25 \leqslant x \leqslant 0.4$ to antiferromagnetic order. The paramagnetic/antiferromagnetic transition is of second order for $0.5 \leqslant x \leqslant 0.65$ and of first order for $x \geqslant 0.7$. For low Mn concentrations, the high-temperature alternating curre...

The magnetic phases of hexagonal perovskites RMnO_3 (R=Ho, Er, Tm, Yb, Sc, Y) are analysed using group theory and the Landau theory of phase transitions. The competition between various magnetic order parameters is discussed in the context of antiferromagnetic interactions. A phenomenological model based on four one-dimensional magnetic order parameters is developed and studied numerically. It is shown that coupling of the various order parameters leads to a complex magnetic ...

From a general model of the Mn oxides R_{1-x}A_{x}MnO_3, we derive an effective Hamiltonian in the low-energy subspace using the projection operator method, in which a novel coupling between the spin and orbital degrees of freedom is included. A phase diagram for temperature T versus doping concentration x is computed by means of Monte Carlo simulation. Our result is consistent with experimental observations in the Mn oxides with relatively wide conduction band, such as Pr_{1...

The phase diagram of doped manganate compounds La_{1-x}A_xMnO_3 (with divalent A) is studied. We analyze an extension of the double exchange model using the Schwinger boson formalism. Earlier work by de Gennes on the existence of a canted phase is reproduced, although this phase is shown to be unstable towards phase separation in a broad regime of physical interest. We numerically solve the model's mean field equations and plot its phase diagram.

A double exchange model for degenerate $e_g$ orbitals with intra- and inter-orbital interactions has been studied for the electron doped manganites A$_{1-x}$B$_{x}$MnO$_3$ ($x > 0.5$). We show that such a model reproduces the observed phase diagram and orbital ordering in the intermediate bandwidth regime and the Jahn-Teller effect, considered to be crucial for the region $x<0.5$, does not play a major role in this region. Brink and Khomskii have already pointed this out and ...

A combination of competing exchange interactions and substitutional disorder gives rise to magnetic inhomogeneities in the [Y$_{2-x}$Mn$_x$]MnMnMn$_4$O$_{12}$ $x = 0.23$ and $x = 0.16$ quadruple perovskite manganites. Our neutron powder scattering measurements show that both the $x = 0.23$ and $x = 0.16$ samples separate into two distinct magnetic phases; below T$_{1}$ = 120 $\pm$ 10 K the system undergoes a transition from a paramagnetic phase to a phase characterised by sho...

Experimental evidence show that in the magnetoresistive manganite Ca_(1-x) Y_xMnO_3, ferromagnetic (FM) polarons arises in an antiferromagnetic (AF) background, as a result of the doping with Yttrium. This hypothesis is supported in this work by classical Monte Carlo (MC) calculations performed on a model where FM Double Exchange (DE) and AF Superexhange (SE) compite.

Understanding the coexistence of ferromagnetism and insulating behavior in manganites is an unsolved problem. We propose a localized-band model involving effective intermediate-range electron-electron (electron-hole) repulsion (attraction) generated by cooperative electron-phonon interaction. Double exchange mechanism, involving holes virtually hopping to nearest neighbors and back, produces magnetic polarons in an antiferromagnetic environment; when these magnetic polarons c...

The chemical influence in the phase separation phenomenon that occurs in perovskite manganites is discussed by means of ab initio calculations. Supercells have been used to simulate a phase separated state, that occurs at Ca concentrations close to the localized to itinerant crossover. We have first considered a model with two types of magnetic ordering coexisting within the same compound. This is not stable. However, a non-isotropic distribution of chemical dopants is found ...

We investigate the phase diagram of an extended Kondo lattice model for doped manganese oxides in the presence of strong but finite Hund's coupling and on-site Coulomb interaction. By means of the Schwinger-boson mean-field approach, it is found that, besides magnetic ordering, there will be non-uniform charge distributions, such as charge ordering and phase separation, if the interaction between electrons prevails over the hybridization. Which of the charge ordering and phas...