Magnetic Interaction in the Geometrically Frustrated Triangular Lattice Antiferromagnet CuFeO2\rm CuFeO_2

The spin wave excitations of the geometrically frustrated triangular lattice antiferromagnet (TLA) $\rm CuFeO_2$ have been measured using high resolution inelastic neutron scattering. Antiferromagnetic interactions up to third nearest neighbors in the ab plane (J_1, J_2, J_3, with $J_2/J_1 \approx 0.44$ and $J_3/J_1 \approx 0.57$), as well as out-of-plane coupling (J_z, with $J_z/J_1 \approx 0.29$) are required to describe the spin wave dispersion relations, indicating a three dimensional character of the magnetic interactions. Two energy dips in the spin wave dispersion occur at the incommensurate wavevectors associated with multiferroic phase, and can be interpreted as dynamic precursors to the magnetoelectric behavior in this system.Comment: 4 pages, 4 figures, published in Phys. Rev. Let

Quantum Phase Transition in the Itinerant Antiferromagnet (V0.9Ti0.1)2O3

Quantum-critical behavior of the itinerant electron antiferromagnet (V0.9Ti0.1)2O3 has been studied by single-crystal neutron scattering. By directly observing antiferromagnetic spin fluctuations in the paramagnetic phase, we have shown that the characteristic energy depends on temperature as c_1 + c_2 T^{3/2}, where c_1 and c_2 are constants. This T^{3/2} dependence demonstrates that the present strongly correlated d-electron antiferromagnet clearly shows the criticality of the spin-density-wave quantum phase transition in three space dimensions.Comment: 4 pages, 4 figure

Course Specifications for New Introductory Courses: Computer Science 227X and 228X

Computer Science 227X introduces first-year students to programming using Scheme. Computer Science 228X is an introduction to data structures in C++. Both courses attempt to teach principles through extensive practice in programming. This document specifies the course\u27s general objectives and gives an overview of what would be taught

The Collinear Magnetic Phases of the Geometrically-Frustrated Antiferromagnet CuFeO2_2: The Importance of Stacking

The correct stacking of hexagonal layers is used to obtain accurate estimates for the exchange and anisotropy parameters of the geometrically-frustrated antiferromagnet CuFeO$_2$. Those parameters are highly constrained by the stability of a collinear metamagnetic phase between fields of 13.5 and 20 T. Constrained fits of the spin-wave frequencies of the collinear \uudd phase below 7 T are used to identify the magnetic unit cell of the metamagnetic \uuudd phase, which contains two hexagonal layers and 10 Fe$^{3+}$ spins.Comment: 3 Figure

Scaling properties of the critical behavior in the dilute antiferromagnet Fe(0.93)Zn(0.07)F2

Critical scattering analyses for dilute antiferromagnets are made difficult by the lack of predicted theoretical line shapes beyond mean-field models. Nevertheless, with the use of some general scaling assumptions we have developed a procedure by which we can analyze the equilibrium critical scattering in these systems for H=0, the random-exchange Ising model, and, more importantly, for H>0, the random-field Ising model. Our new fitting approach, as opposed to the more conventional techniques, allows us to obtain the universal critical behavior exponents and amplitude ratios as well as the critical line shapes. We discuss the technique as applied to Fe(0.93)Zn(0.07)F2. The general technique, however, should be applicable to other problems where the scattering line shapes are not well understood but scaling is expected to hold.Comment: 17 pages, 5 figure

Magnon Damping by magnon-phonon coupling in Manganese Perovskites

Inelastic neutron scattering was used to systematically investigate the spin-wave excitations (magnons) in ferromagnetic manganese perovskites. In spite of the large differences in the Curie temperatures ($T_C$s) of different manganites, their low-temperature spin waves were found to have very similar dispersions with the zone boundary magnon softening. From the wavevector dependence of the magnon lifetime effects and its correlation with the dispersions of the optical phonon modes, we argue that a strong magneto-elastic coupling is responsible for the observed low temperature anomalous spin dynamical behavior of the manganites.Comment: 11 pages, 4 figure

Composts de residuos de caña de azúcar. Capacidad de cesión de boro a la planta

A greenhouse experiment was carried out to determine the capacity of three different composts to release boron gradually to a ryegrass crop. The three composts were made up using the following agricultural wastes: compost BO: 75% sugarcane bagasse, 17% orugo cake and 8% hen manure; compost BG: 78% bagas se and 22% hen manure and compost BT: 95% bagasse and 5% tobacco dust. The composts made up of sugarcane bagasse plus tobacco dust was more effective in releasing boron to the plant than bagasse mixed with orugo and/or hen manure composts. With respect to the form of B release, compost BO did it gradually, compost BG after a long period of integration in the soil and compost BT immediately, during the initial phase of the experiment.Se ha llevado a cabo un experimento de invernadero dedicado a valorar la capacidad que poseen tres composts para suministrar secuencialmente boro a un cultivo de ryegrass. Los composts se prepararon utilizando los siguientes residuos agrícolas: compost BO: 75% residuo de caña de azucar (bagazo), 17% orujo y 7% gallinaza; compost BG: 78% bagazo y 22% gallinaza y compost BT: 95% bagazo y 5% residuo de tabaco. El compost obtenido a partir de bagazo y residuo de tabaco fue mas eficaz para suministrar boro a la planta que los composts que incluían bagazo y orujo y/o gallinaza. Respecto a la forma de cesión de B, el compost BO lo suministró gradualmente,· el compost BG tras un largo período de integración en el suelo y el compost BT inmediatamente, al inicio del experimento

Composts de residuos de caña de azúcar. Capacidad de cesión de boro a la planta

A greenhouse experiment was carri ed out to determi ne the capacity of three different composts to re 1 ease boron gradua 11y to a ryegrass crop. The three composts were made up using the fo110wing agricu1tural wastes: compost BO: 75% sugarcane bagasse, 17% orugo cake and 8% hen manure; compost BG: 78% bagas se and 22% hen manure and compost BT: 95% bagasse and 5% tobacco dust. The composts made up of sugarcane bagasse plus tobacco dust was more effective in re1easing boron to the p1ant than bagasse mixed with orugo and/or hen manure composts. With respect to the form of B re1ease, compost BO did it gradua11y, compost BG after a long period of integration in the soil and compost BT immediate1y, during the initia1 phase of the experimentoSe ha llevado a cabo un experimento de invernadero dedicado a valorar la capa cidad que poseen tres composts para suministrar secuencialmente boro a un cul tivo de ryegrass. Los composts se prepararon utilizando los siguientes resf duos agrícolas: compost BO: 75% resfduo de caña de azucar (bagazo), 17% orujo y 7% ga 11 i naza; compost BG: 78% bagazo y 22% ga 11 i naza y compost BT: 95% ba gazo y 5% resíduo de tabaco. El compost obtenido a partir de bagazo y residuo de tabaco fué mas eficaz para suministrar boro a la planta que los composts que incluían bagazo y orujo y/o gallinaza. Respecto a la forma de cesión de B, el compost BO 10 suministró gradua1mente,·e1 compost BG tras un largo perío do de integración en el suelo y el compost BT inmediatamente, al inicio deT experimento

Anomalous ferromagnetic spin fluctuations in an antiferromagnetic insulator Pr_{1-x}Ca_{x}MnO_{3}

The high temperature paramagnetic state in an antiferromagnetic (AFM) insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin fluctuations with an anomalously small energy scale. The FM fluctuations show a precipitous decrease of the intensity at the charge ordering temperature T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature T_{N}. These results demonstrate the importance of the spin ordering for the complete switching of the FM fluctuation in doped manganites.Comment: REVTeX, 5 pages, 4 figures, submitted to Phys. Rev.