Effects of hydrostatic pressure on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: Evidence for pressure-enhanced antiferromagnetic instability

Hydrostatic pressure effects on the temperature- and magnetic field dependencies of the in-plane and out-of-plane magnetization of the bi-layered perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature value of the paramagnetic susceptibility has been found to systematically decrease with increasing pressure. The effect is accompanied by an increase of the temperature Tmax of a pronounced peak of susceptibility. Thus, magnetization measurements under hydrostatic pressure reveal that the lattice contraction in the structure of Sr3Ru2O7 promotes antiferromagnetism and not ferromagnetism, contrary to the previous beliefs. The effects can be explained by the enhancement of the inter-bi-layer antiferromagnetic spin coupling, driven by the shortening of the superexchange path, and suppression, due to the band-broadening effect, of competing itinerant ferromagnetic correlations.Comment: 11 pages, 4 figure

Ecological mechanisms of sus scrofa population regulation in modern conditions

Wild boar population (Sus scrofa) has been growing rapidly in most countries of the world over the past decades. The invasive species has high reproduction rates and well-developed adaptive responses, which allows it to successfully expand the boundaries of its habitat, create significant economic losses to agriculture and horticulture, urban ecosystems, and threatens the loss of biological diversity and the spread of zoonotic infections. The purpose of the paper was to analyse the factors that contribute to the expansion of the Sus scrofa species in the world, to determine the ecological mechanisms of population regulation against the background of rapid anthropogenic transformation of the habitat and global climatic anomalies; to assess changes in the dynamics of population size in hunting farms of Ukraine for the period from 2010 to 2020 in the Chernihivska oblast, in particular. Conventional methods of retrospective analysis, synthesis, environmental, general biological, and epizootic research were used. The paper analyses the world experience and identifies the main factors of low effectiveness of strategies for controlling the rapidly growing population of wild boar in agroecosystems, mixed forest and urban ecosystems. Due to the unique features of forming a life strategy, the Sus scrofa species demonstrate successful development, expansion of the range of available food resources, effective use of daily diversification of ecological niches in the conditions of transformed ecosystems, etc. It is established that the reason for the inefficiency of ecological mechanisms of pressure on the population of the species in the "predator-prey" system is the absence of large predators in the forest ecosystems of Chernihivska oblast. At the same time, the absence of deterrent mechanisms in the predator-prey system ensured the manifestation of next-level mechanisms, namely, the appearance of foci of African swine fever along the forest cycle in the natural biocenoses of the region. Response – the response of populations was manifested by a rapid short-term decrease in the population of Sus scrofa, as a temporary deterrent effect with a subsequent recovery trend. The results obtained can be used in the development of practical recommendations for biological monitoring, environmental control, and the development of effective forest management measures to prevent biological safety associated with the uncontrolled distribution of Sus scrofa and African swine fever based on universal ecological mechanisms of population regulatio