Magnetic behaviour in Dy1 − xMmxCo2 compounds
The magnetic behaviour in Dy1 − xMmxCo2 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5; Mm = mischmetal) compounds is reported using temperature and field dependence of magnetization (M–T and M–H respectively) measurements. A strong composition dependent irreversibility is observed in both the M–T and M–H scans below the magnetic ordering temperature (TC). A clear change of the first-order magnetic transition of DyCo2 to a second-order one in Dy0.5Mm0.5Co2 is evidenced by M–T and a series of Arrott (M2 versus H/M) plots, obtained from the M–H isotherms around TC. The variation in induced moments of the Co sublattice is estimated. It is found that the Mm substitution can only lead to a considerable reduction in the TC, saturation magnetization, and Co moment. The observed behaviour of M–T and M–H plots with increasing Mm content is discussed in detail.
Butterflylike specific heat, magnetocaloric effect, and itinerant metamagnetism in (Er,Y)Co2 compounds
The field-induced first-order phase transition in (Er{sub 1-x}Y{sub x})Co{sub 2} with the yttrium concentration x = 0.45 is observed to be accompanied by a butterflylike behavior and significant irreversibility of the specific heat. The coefficient {gamma} of the T-linear specific heat decreases by {approx}48% under application and removal of a magnetic field up to 20 kOe. This behavior is attributed to the itinerant electron metamagnetism of Co 3d electrons. The isothermal magnetic entropy change {Delta}S{sub m} in Er{sub 0.55}Y{sub 0.45}Co{sub 2} includes a large contribution associated with spin fluctuations induced by the f-d exchange interaction in the hybridized 3d-5d-electron subsystem. These spin fluctuations are suggested to contribute substantially to the magnetocaloric effect of the RCo{sub 2} type compounds. The maximal {Delta}S{sub m} value observed for ErCo{sub 2} just above the Curie temperature is ascribed to the closeness of the T{sub c} value to the spin-fluctuation temperature T{sub sf} of itinerant Co 3d electrons. The nonmonotonous change in {Delta}S{sub m} with the Curie temperature of R{sub 1-x}R{sub x}{prime}Co{sub 2} compounds is explained by the temperature variation in the spin-fluctuation contribution to the magnetocaloric effect.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.