Structure and magnetic interactions in the solid solution Ba3-xSrxCr2O8

Solid solutions of the magnetic insulators Ba3Cr2O8 and Sr3Cr2O8 (Ba3-xSrxCr2O8) have been prepared in polycrystalline form for the first time. Single crys- talline material was obtained using a mirror image floating zone technique. X-ray diffraction data taken at room temperature indicate that the space group of Ba3-xSrxCr2O8 remains unchanged for all values of x, while the cell parameters depend on the chemical composition, as expected. Magnetization data, measured from 300 K down to 2 K, suggests that the interaction constant Jd within the Cr5+ dimers varies in a peculiar way as a function of x, starting at Jd = 25K for x = 0, then first slightly dropping to Jd = 18K for x = 0.75, before reaching Jd = 62K for x = 3

Spin Gap and the Nature of the 4d3 Magnetic Ground State in the Frustrated FCC Antiferromagnet Ba2YRuO6

The geometrically frustrated double perovskite Ba2YRuO6 has magnetic 4d3 Ru5+ ions decorating an undistorted face-centered cubic (FCC) lattice. This material has been previously reported to exhibit commensurate long-range antiferromagnetic order below T_N = 36K, a factor f = 15 times lower than its Curie-Weiss temperature Theta_CW = -522 K, and purported short-range order to T* = 47K. We report new time-of-flight neutron spectroscopy of Ba2YRuO6 which shows the development of a 5 meV spin gap in the vicinity of the [100] magnetic ordering wavevector below T_N = 36K, with the transition to long-range order occurring at T* = 47K. We also report spin waves extending to 14 meV, a surprisingly small bandwidth in light of the large Theta_CW. We compare the spin gap and bandwidth to relevant neutron studies of the isostructural 4d1 material Ba2YMoO6,and discuss the results in the framework of relatively strong spin-orbit coupling expected in 4d magnetic systems.Comment: 6 pages, 7 figures, Accepted to Physical Review

Jahn-Teller versus quantum effects in the spin-orbital material LuVO3

We report on combined neutron and resonant x-ray scattering results, identifying the nature of the spin-orbital ground state and magnetic excitations in LuVO3 as driven by the orbital parameter. In particular, we distinguish between models based on orbital Peierls dimerization, taken as a signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor of the latter. In order to solve this long-standing puzzle, polarized neutron beams were employed as a prerequisite in order to solve details of the magnetic structure, which allowed quantitative intensity-analysis of extended magnetic excitation data sets. The results of this detailed study enabled us to draw definite conclusions about classical vs quantum behavior of orbitals in this system and to discard the previous claims about quantum effects dominating the orbital physics of LuVO3 and similar systems.Comment: Phys. Rev. B 91, 161104(R) (2015

Investigation of frustrated magnetism in double perovskites

This investigation studies the structural and magnetic properties of the double perovskites Ba2YRuO6, Ba2YReO6,Ba2YOsO6, Ba2MgReO6, Ba2ZnReO6, Ba2Y2/3ReO6, Ba2MgOsO6, Ba2ZnOsO6, Ba2CdOsO6, La2LiRuO6, and La2LiOsO6. These compounds were prepared as powders using conventional solid state techniques. Structural characterization was performed with room temperature powder x-ray diffraction, and for most compounds, room temperature and low temperature powder neutron diffraction. The double perovskites in this investigation can be categorized as cubic Fm-3m and monoclinic P21/n. Over the ranges of temperatures measured, no space group changes were detected. Magnetic susceptibilty, magnetic hysteresis, and heat capacity measurements revealed a variation of ground states and magnetism across this selection of double perovskites. Inelastic neutron scattering experiments gave evidence for spin gap formation in almost all of the compounds.ThesisMaster of Science (MSc

Cancer incidence in sites potentially related to occupational exposures: 58 years of follow-up of firefighters in the Norwegian Fire Departments Cohort

Objectives Firefighters are exposed to a variety of known and suspected carcinogens through their work. However, the association with cancer risk has limited evidence. We examined cancer incidence among firefighters in the newly established Norwegian Fire Departments Cohort restricted to sites with established associations with carcinogens encountered during firefighting. This included sites within the respiratory, urinary, and lympho-hematopoietic systems, and the skin and all sites combined. Methods Male firefighters (N=3881) in the cohort were linked to the Cancer Registry of Norway for incident cancer cases occurring during the period 1960–2018. We calculated standardized incidence ratios (SIR) with rates for the national male population as reference, and stratified SIR analyses by period of first employment, duration of employment, and time since first employment. Results Elevated risk was seen for all sites combined (SIR 1.15, 95% confidence interval 1.07–1.23). Elevated risk of urinary tract cancer was observed among firefighters who began working before 1950, and with observation ≥40 years since first employment. Risk of mesothelioma and laryngeal cancer were elevated with ≥40 years since first employment and with ≥30 years employment duration. Conclusions The observed associations between firefighting and urinary tract cancer, laryngeal cancer, and mesothelioma have been observed in some studies previously, and our results suggest the observed elevated risks are related to carcinogenic occupational exposures. Differences in risk by period of employment potentially reflect changes in exposures from improved quality and use of personal protective equipment.publishedVersio

Occupational exposures of firefighting and urinary tract cancer risk among men in the Norwegian Fire Departments Cohort

Objectives Increased risks of bladder cancer and mesothelioma were the strongest evidence for the recent reclassification of firefighting as carcinogenic (Group 1) by the International Agency for Research on Cancer. Our study aim was to develop indicators for specific firefighting exposures and examine associations with urinary tract cancer (UTC), including bladder cancer. Methods We developed indicators for exposure from employment at a fire department or in firefighting jobs, to fire and smoke, and to diesel exhaust for men in the Norwegian Fire Departments Cohort (n=4250). Incident UTC cases were obtained from the Cancer Registry of Norway (1960–2021). Poisson regression was used to estimate incidence rate ratios (IRR) with cumulative exposures grouped into tertiles (reference: lowest exposed tertile) with 0-year, 10-year and 15-year lagging of exposures. Results During 125 090 person-years of follow-up, there were 76 cases of UTC. IRRs were mostly non-significantly increased in the middle tertile and at or below 1 in the highest tertile for total duration of employment, number of fires attended and fire exposure score with and without lags. In the middle tertile for diesel exhaust exposure, UTC risk was elevated over twofold with 10-year (IRR 2.27, 95% CI 1.22 to 4.20) and 15- year (2.21, 1.18 to 4.16) lags, and near 1 in the highest tertile. Findings for bladder cancer were similar to those for UTC. Conclusions Dose-response associations between the exposure indicators and UTC were not observed. Future studies using the indicators with more cases are needed.publishedVersio