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We study the electronic structure of single-crystal ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$, a non-charge-ordered mixed-valent semiconductor which exhibits a glassy magnetic ground state. We use the techniques of soft x-ray photoemission, hard x-ray photoemission, x-ray absorption, and resonant photoemission spectroscopy to investigate the occupied and unoccupied electronic states of ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. Core level photoemission and x-ray absorption spectroscopy allow us to determine the valence states of Tb, Sr, and Mn ions in ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$. Model charge transfer multiplet calculations of core level photoemission and x-ray absorption spectra are employed to separate out the ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ states and confirm their relative concentrations. Resonant photoemission spectroscopy across the Mn $2p\text{\ensuremath{-}}3d$ threshold shows clear resonant enhancement of the Mn $3d$ partial density of states and two-hole correlation satellites. A Cini-Sawatzky analysis gives on-site Coulomb energy ${U}_{dd}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}5.5\ifmmode\pm\else\textpm\fi{}0.2$ eV for the Mn $3{d}^{n}$ states and ${U}_{pd}$ = 0.7 $\mathrm{eV}\ifmmode\pm\else\textpm\fi{}0.2$ eV for the Mn $3{d}^{n+1}{\underline{L}}^{1}$ states. The O $1s\text{\ensuremath{-}}2p$ resonant photoemission is used to identify the O $2p$ two-hole correlation satellite which provides ${U}_{pp}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}3.4\ifmmode\pm\else\textpm\fi{}0.2$ eV for the O $2p$ states. Valence band photoemission indicates a small-gap semiconductor ($l100$ meV) consistent with electrical transport measurements. The estimated electronic structure parameters of the on-site Coulomb energies, in combination with the charge transfer energy and the hybridization strength obtained from the model calculations, indicate that ${\mathrm{Tb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ is a strongly correlated charge transfer type semiconductor.

The perovskite ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ shows two anomalies in its magnetic susceptibility at ${T}_{N}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}257$ K and ${T}_{\mathrm{SR}}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}190$ K which are, respectively, the antiferromagnetic and spin-reorientation transition that occur in the Fe/Cr sublattice. Magnetic susceptibility of this compound reveals canonical signatures of a Griffiths-like phase: a negative deviation from the ideal Curie-Weiss law and in less-than-unity power-law susceptibility exponents. Neutron-diffraction data analysis confirms two spin-reorientation transitions in this compound. The first one from ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${\mathrm{C}}_{x}, {\mathrm{G}}_{y}, {\mathrm{F}}_{z}$) to ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${\mathrm{A}}_{x}, {\mathrm{F}}_{y}, {\mathrm{G}}_{z}$) occurs at ${T}_{N}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}257$ K and a second one from ${\mathrm{\ensuremath{\Gamma}}}_{4}$ (${\mathrm{A}}_{x}, {\mathrm{F}}_{y}, {\mathrm{G}}_{z}$) to ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${\mathrm{C}}_{x}, {\mathrm{G}}_{y}, {\mathrm{F}}_{z}$) at ${T}_{\mathrm{SR}}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}190$ K in the $Pnma$ space-group setting. The ${\mathrm{\ensuremath{\Gamma}}}_{2}$ (${\mathrm{C}}_{x}, {\mathrm{G}}_{y}, {\mathrm{F}}_{z}$) structure is stable down to 7.7 K, leading to an ordered moment of 3.34(1) ${\ensuremath{\mu}}_{\mathrm{B}}/{\mathrm{Fe}}^{3+}({\mathrm{Cr}}^{3+}$). In addition to the long-range magnetic order, experimental indication of diffuse magnetism is observed in neutron-diffraction data at 7.7 K. Tb develops a ferromagnetic component along the $z$ axis at 20 K. Thermal conductivity and spin-phonon coupling of ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ studied through Raman spectroscopy are also presented in the paper. The magnetic anomalies at ${T}_{N}$ and ${T}_{\mathrm{SR}}$ do not appear in the thermal conductivity of ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$, which appears to be robust up to 9 T. On the other hand, they are revealed in the temperature dependence of full-width-at-half-maximum curves derived from Raman intensities. An antiferromagnetic structure with $\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\downarrow}$ arrangement of Fe/Cr spins is found as the ground state through first-principles energy calculations, supporting the experimentally determined magnetic structure at 7.7 K. The spin-resolved total and partial density of states show that ${\mathrm{TbFe}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ is insulating with a band gap of $\ensuremath{\sim}0.12$ (2.4) eV within GGA ($\mathrm{GGA}+U$) functionals.

The double perovskite Y2NiMnO6 displays ferromagnetic transition at T-c approximate to 81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (Ms) and also validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The cation-ordered P2(1)/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of the frequency-dependent dielectric constant and equivalent circuit analysis of impedance data take into account the bulk contribution to the total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (T-c). Pyrocurrent measurements register a current flow with onset near T-c and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to reorientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material.

Unusual behavior of reentrant spin-glass (RSG) compound Lu2MnNiO6 has been investigated by magnetometry and neutron diffraction. The system possesses a ferromagnetic (FM) ordering below 40 K and undergoes a RSG transition at 20 K. Additionally, Lu2MnNiO6 retains memory effect above the glassy transition till spins sustain ordering. A novel critical behavior with unusual critical exponents (beta =similar to 0.241 and gamma similar to 1.142) is observed that indicates a canting in the spin structure below the ferromagnetic transition (T-C). A comprehensive analysis of temperature-dependent neutron diffraction data and first-principles calculations divulge that a structural distortion induced by an octahedral tilting results in a canted spin structure below T-C.

Variable temperature scanning tunneling microscopy/spectroscopy studies on single crystals and epitaxial thin films of hole-doped manganites, which show colossal magnetoresistance, have been done. We have investigated the variation of the density of states, at and near the Fermi energy ($E_f$), as a function of temperature. Simple calculations have been carried out, to find out the effect of temperature on the tunneling spectra and extract the variation of density of states with temperature, from the observed data. We also report here, atomic resolution images, on the single crystals and larger range images showing the growth patterns on thin films. Our investigation shows unambiguously that there is a rapid variation in density of states for temperatures near the Curie temperature ($T_c$). While for temperatures below $T_c$, a finite DOS is observed at $E_f$, for temperatures near $T_c$ a hard gap opens up in the density of states near $E_f$. For temperatures much higher than $T_c$, this gap most likely gives way to a soft gap. The observed hard gap for temperatures near $T_c$, is somewhat higher than the transport gap for all the materials. For different materials, we find that the magnitude of the hard gap decreases as the $T_c$ of the material increases and eventually, for materials with a $T_c$ close to 400 K, the value of the gap approaches zero., 9 pages RevTeX, 12 postscript figures, 1 table included in text, submitted to Physical Review B

The critical properties of orthorhombic Pr${}_{0.6}$Sr${}_{0.4}$MnO${}_{3}$ single crystals were investigated by a series of static magnetization measurements along the three different crystallographic axes as well as by specific heat measurements. A careful range-of-fitting-analysis of the magnetization and susceptibility data obtained from the modified Arrott plots shows that Pr${}_{0.6}$Sr${}_{0.4}$MnO${}_{3}$ has a very narrow critical regime. Nevertheless, the system belongs to the three-dimensional (3D) Heisenberg universality class with short-range exchange. The critical exponents obey Widom scaling and are in excellent agreement with the single scaling equation of state $M(H,\ensuremath{\epsilon})={|\ensuremath{\epsilon}|}^{\ensuremath{\beta}}{f}_{\ifmmode\pm\else\textpm\fi{}}{(H/|\ensuremath{\epsilon}|}^{(\ensuremath{\beta}+\ensuremath{\gamma})}$; with ${f}_{+}$ for $Tg{T}_{c}$ and ${f}_{\ensuremath{-}}$ for $Tl{T}_{c}$. A detailed analysis of the specific heat that account for all relevant contributions allows us to extract and analyze the contribution related to the magnetic phase transition. The specific heat indicates the presence of a linear electronic term at low temperatures and a prominent contribution from crystal field excitations of Pr. A comparison with data from literature for PrMnO${}_{3}$ shows that a Pr-Mn magnetic exchange is responsible for a sizable shift in the lowest lying excitation.

Hexagonal Dy(0.5)Y(0.5)MnO(3), a multiferroic rare-earth manganite with geometrically frustrated antiferromagnetism, has been investigated with single-crystal neutron diffraction measurements. Below 3.4 K magnetic order is observed on both the Mn (antiferromagnetic) and Dy (ferrimagnetic) sublattices that is identical to that of undiluted hexagonal DyMnO(3) at low temperature. The Mn moments undergo a spin reorientation transition between 3.4 K and 10 K, with antiferromagnetic order of the Mn sublattice persisting up to 70 K; the antiferromagnetic order in this phase is distinct from that observed in undiluted (h) DyMnO(3), yielding a qualitatively new phase diagram not seen in other hexagonal rare-earth manganites. A magnetic field applied parallel to the crystallographic c axis will drive a transition from the antiferromagnetic phase into the low-temperature ferrimagnetic phase with little hysteresis.

We investigate the structural, magnetic, and specific heat behavior of the hexagonal manganite Dy0.5Y0.5MnO3 in order to understand the effect of dilution of Dy magnetism with nonmagnetic yttrium. In this compound, the triangular Mn lattice orders antiferromagnetic at T-N(Mn) approximate to 68 K observed experimentally in the derivative of magnetic susceptibility as well as in specific heat. In addition, a low-temperature peak at T-N(Dy) similar to 3 K is observed in specific heat which is attributed to rare earth order. The T-N(Mn) increases by 9 K compared to that of hexagonal (h) DyMnO3 while T-N(Dy) is unchanged. A change in slope of thermal evolution of lattice parameters is observed to occur at temperature close to T-N(Mn). This hints at strong magnetoelastic coupling in this geometric multiferroic. In magnetization measurements, steplike features are observed when the magnetic field is applied along the c axis which shift to higher fields with temperature and vanish completely above 40 K. The presence of different magnetic phases at low temperature and strong magnetoelastic effects can lead to such field-induced transitions which resemble metamagnetic transitions. This indicates the possibility of strong field-induced effects in dielectric properties of this material, which is unexplored to date.

We have investigated the influence of Fe excess on the electrical transport and magnetism of Fe1+yTe0.5Se0.5 (y=0.04 and 0.09) single crystals. Both compositions exhibit resistively determined superconducting transitions (T-c) with an onset temperature of about 15 K. From the width of the superconducting transition and the magnitude of the lower critical field H-c1, it is inferred that excess of Fe suppresses superconductivity. The linear and nonlinear responses of the ac susceptibility show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is a magnetic coupling between Fe excess occupying interstitial sites in the chalcogen planes and those in the Fe-square lattice. The temperature derivative of the resistivity d(rho)/d(T) in the temperature range T-c < T < T-a with T-a being the temperature of a magnetic anomaly, changes from positive to negative with increasing Fe. A log 1/T divergence of the resistivity above T-c in the sample with higher amount of Fe suggests a disorder-driven electronic localization.

Single crystals of $La_{0.7–-y}Nd_yPb_{0.3}MnO_3$ with different y are grown by flux growth technique. The influence of change in average cationic radius $(\langle r_A\rangle)$ and cation size disorder $(\sigma^2)$ on the transport and magnetic properties of these crystals due to the presence of different cations (La and Nd) on the rare-earth sRd site is studied. Curie temperature $T_C$ and metal-insulator transition temperature $T_M_I$ are sensitive to the R site occupation. The temperature dependence of magnetization of $La_{0.7}Nd_yPb_{0.3}MnO_3$ is consistent with spin wave excitations according to the Bloch $T^{3/2}$ law at zero magnetic field limit. The Nd-based systems follow $T^{3/2}$ law only in a certain range of temperature and deviate at low temperatures, which is ascribed to a probably canted ordering of Nd and Mn moments with an antiferromagnetic component at very low temperatures. The values of spin stiffness constants and saturation magnetization vary systematically with changing occupation on the R site. Specific heat measurements of Nd containing samples show a Schottky-like anomaly at low temperature (below 15 K), which increases with the concentration of Nd ions in the lattice. It is concluded that the magnetic properties of manganites with Nd are affected by a tendency for magnetic ordering of the Nd ions.

Results of a study of dc magnetization $M(T,H),$ performed on a ${\mathrm{Nd}}_{0.6}{\mathrm{Pb}}_{0.4}{\mathrm{MnO}}_{3}$ single crystal in the temperature range around ${T}_{C}$ (Curie temperature) which embraces the supposed critical region $|\ensuremath{\varepsilon}|=|T\ensuremath{-}{T}_{C}|{/T}_{C}l~0.05$ are reported. The magnetic data analyzed in the critical region using the Kouvel-Fisher method give the values for the ${T}_{C}=156.47\ifmmode\pm\else\textpm\fi{}0.06\mathrm{K}$ and the critical exponents $\ensuremath{\beta}=0.374\ifmmode\pm\else\textpm\fi{}0.006$ (from the temperature dependence of magnetization) and $\ensuremath{\gamma}=1.329\ifmmode\pm\else\textpm\fi{}0.003$ (from the temperature dependence of initial susceptibility). The critical isotherm ${M(T}_{C},H)$ gives $\ensuremath{\delta}=4.54\ifmmode\pm\else\textpm\fi{}0.10.$ Thus the scaling law $\ensuremath{\gamma}+\ensuremath{\beta}=\ensuremath{\delta}\ensuremath{\beta}$ is fulfilled. The critical exponents obey the single scaling equation of state $M(H,\ensuremath{\varepsilon})={\ensuremath{\varepsilon}}^{\ensuremath{\beta}}{f}_{\ifmmode\pm\else\textpm\fi{}}(H/{\ensuremath{\varepsilon}}^{\ensuremath{\beta}+\ensuremath{\gamma}}),$ where ${f}_{+}$ for $Tg{T}_{C}$ and ${f}_{\ensuremath{-}}$ for $Tl{T}_{C}.$ The exponent values are very close to those expected for the universality class of three-dimensional Heisenberg ferromagnets with short-range interactions.