Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2

Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity, and specific heat measurements carried out in wide temperature and magnetic field ranges. Moreover, the electronic structure of the compound was studied at room temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The physical properties were analyzed in terms of crystalline electric field and compared with results of ab-initio band structure calculations performed within the density functional theory approach. The compound was found to crystallize in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma -- No.74, Pearson symbol: oI24) with the lattice parameters: a = 7.1330(14) A, b = 9.7340(19) A, and c = 5.6040(11) A. Analysis of the magnetic and XPS data revealed the presence of well localized magnetic moments of trivalent cerium ions. All physical properties were found to be highly anisotropic over the whole temperature range studied, and influenced by exceptionally strong crystalline electric field with the overall splitting of the 4f1 ground multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic moments at TN = 4.70(1)K and their subsequent spin rearrangement at Tt = 4.48(1) K manifest themselves as distinct anomalies in the temperature characteristics of all investigated physical properties and exhibit complex evolution in an external magnetic field. A tentative magnetic B-T phase diagram, constructed for B parallel to the b-axis being the easy magnetization direction, shows very complex magnetic behavior of CeRh3Si2, similar to that recently reported for an isostructural compound CeIr3Si2. The electronic band structure calculations corroborated the antiferromagnetic ordering of the cerium magnetic moments and well reproduced the experimental XPS valence band spectrum.Comment: 32 pages, 12 figures, to appear in Physical Review

Violation of critical universality at the antiferromagnetic phase transition of YbRh2Si2

We report on precise low-temperature specific-heat measurements, C(T), of YbRh2Si2 in the vicinity of the antiferromagnetic phase transition on a single crystal of superior quality (RRR 150). We observe a very sharp peak at T_N=72mK with absolute values as high as C/T=8J/molK^2. A detailed analysis of the critical exponent \alpha around T_N reveals \alpha=0.38 which differs significantly from those of the conventional universality classes in the Ginzburg-Landau theory, where \alpha<0.11. Thermal-expansion measurements corroborate this large positive critical exponent. These results provide insight into the nature of the critical magnetic fluctuations at a temperature-driven phase transition close to a quantum critical point.Comment: Accepted for PR

Cropping system effects on soil quality in the Great Plains: Synthesis from a regional project

Soils perform a number of essential functions affecting management goals. Soil functions were assessed by measuring physical, chemical, and biological properties in a regional assessment of conventional (CON) and alternative (ALT) management practices at eight sites within the Great Plains. The results, reported in accompanying papers, provide excellent data for assessing how management practices collectively affect agronomic and environmental soil functions that benefit both farmers and society. Our objective was to use the regional data as an input for two new assessment tools to evaluate their potential and sensitivity for detecting differences (aggradation or degradation) in management systems. The soil management assessment framework (SMAF) and the agro-ecosystem performance assessment tool (AEPAT) were used to score individual soil properties at each location relative to expected conditions based on inherent soil-forming factors and to compute index values that provide an overall assessment of the agronomic and environmental impact of the CON and ALT practices. SMAF index values were positively correlated with grain yield (an agronomic function) and total organic matter (an agronomic and environmental function). They were negatively correlated with soil nitrate concentration at harvest (an indicator of environmental function). There was general agreement between the two assessment tools when used to compare management practices. Users can measure a small number of soil properties and use one of these tools to easily assess the effectiveness of soil management practices. A higher score in either tool identifies more environmentally and agronomically sustainable management. Temporal variability in measured indicators makes dynamic assessments of management practices essential. Water-filled pore space, aggregate stability, particulate organic matter, and microbial biomass were sensitive to management and should be included in studies aimed at improving soil management. Reductions in both tillage and fallow combined with crop rotation has resulted in improved soil function (e.g., nutrient cycling, organic C content, and productivity) throughout the Great Plains

Lentil green manure as fallow replacement in the semiarid northern Great Plains

Green manures (GM) may offset inorganic N needs and improve soil quality. Study objectives were to determine effects of green manure on soil-N fertility, water use, soil quality, and yield of spring wheat (Triticum aestivum L.). On two treatments, lentil (Lens culinaris Medikus cv. Indianhead) was green manured in a green manure–spring wheat rotation. Lentil was killed by disking (GMMF) or chemicals (GMCF). Additional treatments were annually cropped wheat (AW) in a mechanical fallow (MF) or chemical fallow (CF) sequence. No inorganic N was used on GMMF and GMCF. Experiments were started in 1991 on a Williams loam (fine-loamy, mixed Typic Argiboroll) near Culbertson, MT. Green-manure treatments used 56 mm more water than fallow treatments when lentil was grown to lower-pod set. When lentil was killed at full bloom, there were no differences in water use among GM and fallow treatments. There were no differences among treatments in soil water at wheat planting. Wheat yield was 25% less on GM than on MF and CF. Soil NO 3–N (0-0.6 m) was 35% less on GM than MF and CF rotations. There were no differences in soil quality indicators of bulk density, organic C, pH, electrical conductivity, and deep NO3–N (0.6 –1.8 m) among treatments after two cycles of GM. Potentially mineralizable N was 66% greater on GM treatments than on fallow treatments. Short-term results (5 yr) show that available N limited wheat production more than did soil water on the GM treatments. Soil improvement using green manures may require many additional cropping cycles

Kondo-Cluster-Glass State near a Ferromagnetic Quantum Phase Transition

We report on a comprehensive study of CePd$_{1-x}$Rh$_x$ $(0.6 \leq x \leq 0.95)$ poly- and single crystals close to the ferromagnetic instability by means of low-temperature ac susceptibility, magnetization and volume thermal expansion. The signature of ferromagnetism in this heavy-fermion system can be traced from 6.6 K in CePd down to 25 mK for $x=0.87$. Despite pronounced non-Fermi-liquid (NFL) effects in both, specific heat and thermal expansion, the Gr\"uneisen ratio {\it does not} diverge as $T\to 0$, providing evidence for the absence of a quantum critical point. Instead, a peculiar "Kondo-cluster-glass" state is found for $x\geq 0.65$, and the NFL effects in the specific heat, ac susceptibility and magnetization are compatible with the quantum Griffiths phase scenario.Comment: 4 pages, 4 figure

Bowen-Ratio Comparisons with Lysimeter Evapotranspiration

Water use in agriculture by different cropping systems is of interest in determining crop water use efficiency of different tillage practices that will lead to reduced crop production risk. Lysimeters are considered the standard for evapotranspiration (ET) measurements; however, these units are often not replicated and are few in number at any given location. Our objective was to determine if a simple Bowen-ratio system with nonexchanging psychrometers could provide accurate measurements of ET from lentil (Lens culinaris Medikus) in a semiarid climate. The study was conducted in 1993 and 1994 on two adjacent 180- by 180-m fields with weighing lysimeters (1.68 by 1.68 by 1.83 m) located in the center of each field, on a Williams loam (fine-loamy, mixed Typic Argiboroll) soil near Sidney, MT. A Bowen-ratio system comprised of two nonexchanging psychrometers and anemometers at 0.25 and 1.25 m above the plant canopy surface was placed in the lentil field along with a net radiometer and soil heat flux plate. Precipitation during the growing season from planting to swathing was 367 mm in 1993 and 227 mm in 1994. In 1993, soil water content of the lysimeter was greater than the field after large precipitation events around Day of Year (DOY) 210, even though the lysimeter was drained. After this time, the lysimeter ET exceeded that measured by the Bowen-ratio system. Agreement was closer in 1994, when precipitation was near normal and there was no excess soil water in the lysimeter. Cumulative ET totals from the lysimeter were reflective of the seasonal precipitation patterns. Differences between the lysimeter and Bowen-ratio occurred when there was excess precipitation and inadequate drainage from the lysimeter. Half-hourly ET fluxes from lysimeter and Bowen-ratio values agreed to within 10% throughout the season. Bowen-ratio systems with nonexchanging psychrometers can provide satisfactory estimates of daily and seasonal ET and can be used to estimate ET in semiarid climates

Lentil water use and fallow water loss in a semiarid climate

With renewed interest in legumes for green manures or as partial summer fallow replacement crops, it is important to know water requirements of these crops in semiarid agriculture. Our objective was to evaluate seasonal water use by black lentil (Lens culinaris Medikus cv. Indianhead), a potential fallow replacement crop, and to relate water use to parameters useful as soil water management tools. We measured evapotranspiration (ET) from two precision weighing lysimeters located on a Williams loam (fine-loamy, mixed Typic Argiboroll) near Sidney, MT. The lysimeters were in adjacent 180- by 180-m fields in a typical strip-crop environment of the semiarid northern Great Plains. Bowen ratio estimates of ET were also obtained. Lentil was seeded no-till into wheat (Triticum aestivum L.) stubble on one lysimeter field in 1993, and the other was left in chemical fallow. Seeded and fallow fields were rotated in 1994. Water loss by ET from lentil and fallow lysimeters was the same ( 25 mm) for 3 wk following seeding. Plant height was related to growing degree days (GDD) in both years. Cumulative ET was related to GDD for both years until about 800 GDD, corresponding to nearly 300 mm ET. Deciding how much water to sacrifice (with hopes of recovery during the noncrop period) becomes a matter of judgment about probable rainfall. At full bloom ( 2 Mg ha' dry matter production), the lentil crop used about 50 to 70 mm more water than fallow. Probably no more than 50 mm of water loss above that from fallow should be sacrificed if a grain crop is to be seeded the following year. From a practical standpoint, because plant height was closely related to both GDD and cumulative ET, it is plausible that a simple measure of lentil height (about 350 mm maximum) can give sufficient accuracy for determining when lentil growth, as a partial summer fallow replacement crop in a semiarid climate, should be terminated