Ordering in weakly coupled random singlet spin chains

The influence of bond randomness on long range magnetic ordering in the weakly coupled S = 1/2 antiferromagnetic spin chain materials Cu(py)2(Cl1-xBrx)2 is studied by muon spin rotation and bulk measurements. Disorder is found to have a strong effect on the ordering temperature TN, and an even stronger one on the saturation magnetization m0, but considerably more so in the effectively lower-dimensional Br-rich materials. The observed behavior is attributed to Random Singlet ground states of individual spin chains, but remains in contradiction with chain mean field theory predictions. In this context, we discuss the possibility of a universal distribution of ordered moments in the weakly coupled Random Singlet chains model

MnWO4, calorimetric study of the bifurcated antiferromagnetic anomaly

The heat capacity of a powdered MnWO4 sample has been measured from 5–350 K. The data show three anomalies below 20 K: a small peak at 6.8±0.1 K, then two large sharp peaks at 12.57±0.05 and 13.36±0.05 K. The magnetic entropy was measured as R ln 6. The data between 5 and 11.5 K obeys a power law dependence Cmag=ATB where B=1.73. The sharp double peak is similar to the bifurcated anomaly in MnCl2 which originates from two distinct antiferromagnetic phases, reported by R. B. Murray et al. The double anomaly is discussed in terms of the superexchange properties of MnWO4.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87559/2/445_1.pd

Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)2_2(ClO4_4)2_2

Cu(pz)$_2$(ClO$_4$)$_2$ (with pz denoting pyrazine C$_4$H$_4$N$_2$) is a two-dimensional spin-1/2 square-lattice antiferromagnet with $T_{\mathrm{N}}$ = 4.24 K. Due to a persisting focus on the low-temperature magnetic properties, its room-temperature structural and physical properties caught no attention up to now. Here we report a study of the structural features of Cu(pz)$_2$(ClO$_4$)$_2$ in the paramagnetic phase, up to 330 K. By employing magnetization, specific heat, $^{35}$Cl nuclear magnetic resonance, and neutron diffraction measurements, we provide evidence of a second-order phase transition at $T^{\star}$ = 294 K, not reported before. The absence of a magnetic ordering across $T^{\star}$ in the magnetization data, yet the presence of a sizable anomaly in the specific heat, suggest a structural order-to-disorder type transition. NMR and neutron-diffraction data corroborate our conjecture, by revealing subtle angular distortions of the pyrazine rings and of ClO$^-_4$ counteranion tetrahedra, shown to adopt a configuration of higher symmetry above the transition temperature.Comment: 10 pages, 12 figure

Identifying Stakeholders’ Needs for Agricultural Communications in Higher Education Curriculum in Australia

Agriculture is a vital part of the Australian economy. With an industry poised for growth, and a growing disconnect between consumers and agriculture, additional communication efforts are needed. The purpose of this study was to complete a curriculum visioning process to inform agricultural communications curriculum development in Australia. This study used a qualitative research design consisting of face-to-face, semi-structured interviews with individuals from 14 agricultural organizations and two universities. The results indicated the industry is addressing many challenges, but also has opportunities that would benefit from strategic communication efforts. Participants provided suggestions regarding the specific communication skills and agriculture knowledge future employees should possess. Recognizing these competencies informed the curriculum visioning process for agricultural communications as an academic discipline within Australian higher education. Recommendations for both practice and future research are provided