Crystal and magnetic structure of the La1−x_{1-x}Cax_{x}MnO3_{3} compound (x=0.8,0.85)(x=0.8,0.85)

We studied the crystal and magnetic structure of the La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound for $x=0.8$ and $x=0.85$. At T=300 K both samples are paramagnetic with crystallographic symmetry $Pnma$. At low temperatures they undergo a monoclinic distortion from orthorhombic $Pnma$-type structure with $a_p\sqrt{2}\times 2a_p\times a_p\sqrt{2}$ to a monoclinic structure with ($a_p\sqrt{2}\times 2a_p\times a_p\sqrt{2}$, $\beta=90+\epsilon\sim 91.4^{\rm o}$) and $P2_1/m$ space group below $T_N$. The onset of the structural transformation coincides with the development of the $C$-type long range antiferromagnetic order with propagation vector ${\bf k}=({1/2},0,{1/2})$. The monoclinic unit cell allowed us to determine the direction of the Mn magnetic moment with respect to the crystallographic axes: it is perpendicular to the propagation vector, ${\bf m}\perp {\bf k}=({1/2},0,{1/2})$. The amplitude of the ordered magnetic moment at $T=1.6$ K is found to be $2.53(2)$ and $2.47(2)\mu_{B}$ for $x=0.8$ and 0.85, respectively.Comment: In press (Phys. Rev B 01 Feb 2002

Phase diagram of the La1−x_{1-x}Cax_{x}MnO3_{3} compound for 0.5≤x≤0.90.5\leq x\leq 0.9

We have studied the phase diagram of La$_{1-x}$Ca$_{x}$MnO$_{3}$ for $0.5\leq x\leq 0.9$ using neutron powder diffraction and magnetization measurements. At 300 K all samples are paramagnetic and single phase with crystallographic symmetry $Pnma$. As the temperature is reduced a structural transition is observed which is to a charge-ordered state only for certain x. On further cooling the material passes to an antiferromagnetic ground state with Neel temperature $T_N$ that depends on x. For $0.8\leq x\leq 0.9$ the structural transformation occurs at the same temperature as the magnetic transition. Overall, the neutron diffraction patterns were explained by considering four phase boundaries for which La$_{1-x}$Ca$_x$MnO$_3$ forms a distinct phase: the CE phase at $x=0.5-0.55$, the charge-ordered phase at x=2/3, the monoclinic and C-type magnetic structure at $x=0.80-0.85$ and the G-type magnetic structure at x=1. Between these phase boundaries the magnetic reflections suggest the existence of mixed compounds containing both phases of the adjacent phase boundaries in a ratio determined by the lever rule

Management earnings forecasts and IPO performance: evidence of a regime change

Companies undertaking initial public offerings (IPOs) in Greece were obliged to include next-year profit forecast in their prospectuses, until the regulation changed in 2001 to voluntary forecasting. Drawing evidence from IPOs issued in the period 1993–2015, this is the first study to investigate the effect of disclosure regime on management earnings forecasts and IPO long-term performance. The findings show mainly positive forecast errors (forecasts are lower than actual earnings) and higher long-term returns during the mandatory period, suggesting that the mandatory disclosure requirement causes issuers to systematically bias profit forecasts downwards as they opt for the safety of accounting conservatism. The mandatory disclosure requirement artificially improves IPO share performance. Overall, our results show that mandatory disclosure of earnings forecasts can impede capital market efficiency once it goes beyond historical financial information to involve compulsory projections of future performance

Mössbauer study of 1% 57 Fe doped ferromagnetic insulator La 0.825 Ca 0.175 MnO 3

We have employed magnetization measurements, Mössbauer and ESR spectroscopic techniques, in order to study the ferromagnetic insulating (FMI) compound La 1-x Ca xMnO 3 (x=0.175) doped with 1% 57 Fe. We have used two samples; one prepared in air which has cation vacancies and a second in inert atmosphere, which is stoichiometric. An abrupt change of the experimental results is obtained, by all techniques, in the ferromagnetic insulating regime, in the temperature region of T O/O// ≈60 K, where an orbital rearrangement is suggested to occur. An analysis of these findings points to an orbital rearrangement transformation. Ferromagnetic resonance reveals considerable differences between stoichiometric and cation deficient samples, indicating anisotropy of the exchange interactions in the former sample with significant temperature dependence, most pronounced in the vicinity of T O/O// Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005

Effects of Co, Fe, and Al doping on the oxygen disordering and superconducting transition temperature of YBa₂Cu₃O₆₊_x

Using computer simulation on a model of oxygen ordering in the basal Cu1−yMyOx plane of the high-temperature superconductor YBa2Cu3−yMyO6+x, we show that the effect of substituting Cu with M = Co, Fe, or Al is a diminishing of the oxygen-ordered orthorhombic domain sizes and eventually a breakdown of the orthorhombic structure. The model accounts for experimental structural data. By use of a previously established minimal model, which connects the superconducting transition temperature, Tc, to the formation of specific ordered orthorhombic domains in the undoped material, we show that the detrimental effect on Tc by metal-ion doping as well as oxygen depletion becomes manifest in a unified way as a result of oxygen disorderin