Weak magnetic anisotropy in GdRh2_2Si2_2 studied by magnetic resonance

The antiferromagnetically (AFM) ordered state of GdRh$_{2}$Si$_{2}$ which consists of AFM-stacked ferromagnetic layers is investigated by magnetic resonance spectroscopy. The almost isotropic Gd$^{3+}$ paramagnetic resonance becomes anisotropic in the AFM ordered region below 107 K. The emerging internal anisotropic exchange-fields are still small enough to allow an investigation of their magnetization dynamics by using a standard microwave-frequency magnetic resonance technique. We could characterize this anisotropy in detail in the ferromagnetic layers of the excitation at 9 and 34 GHz. We derived a resonance condition for the AFM ordered phase to describe the weak in-plane anisotropic behaviour in combination with a mean-field analysis.Comment: 7 page

GdRh2_2Si2_2: An exemplary tetragonal system for antiferromagnetic order with weak in-plane anisotropy

The anisotropy of magnetic properties commonly is introduced in textbooks using the case of an antiferromagnetic system with Ising type anisotropy. This model presents huge anisotropic magnetization and a pronounced metamagnetic transition and is well-known and well-documented both, in experiments and theory. In contrast, the case of an antiferromagnetic $X$-$Y$ system with weak in-plane anisotropy is only poorly documented. We studied the anisotropic magnetization of the compound GdRh$_2$Si$_2$ and found that it is a perfect model system for such a weak-anisotropy setting because the Gd$^{3+}$ ions in GdRh$_2$Si$_2$ have a pure spin moment of S=7/2 which orders in a simple AFM structure with ${\bf Q} = (001)$. We observed experimentally in $M(B)$ a continuous spin-flop transition and domain effects for field applied along the $[100]$- and the $[110]$-direction, respectively. We applied a mean field model for the free energy to describe our data and combine it with an Ising chain model to account for domain effects. Our calculations reproduce the experimental data very well. In addition, we performed magnetic X-ray scattering and X-ray magnetic circular dichroism measurements, which confirm the AFM propagation vector to be ${\bf Q} = (001)$ and indicate the absence of polarization on the rhodium atoms

Procedurally Fair Provision of Public Projects An axiomatic characterization

Unanimous voting as the fundamental procedural source of political legitimacy grants veto power to each individual. We present an axiomatic characterization of a class of bidding processes to spell out the underlying egalitarian values for collective projects of a "productive state". At heart of such procedures is the determination of payments for all possible bid vectors such that equal "profits" according to bids emerge. Along with other intuitive requirements this characterizes procedurally fair bidding rules for advantageous projects of a collectivity.Unanimity in Collective Decision Making, Buchanan, Wicksell

(Over-)Stylizing Experimental Findings and Theorizing with Sweeping Generality

Human decision making is a process guided by different and partly competing motivations that can each dominate behavior and lead to different effects depending on strength and circumstances. 'Over-stylizing' neglects such competing concerns and context-dependence, although it facilitates the emergence of elaborate general theories. We illustrate by examples from social dilemma experiments and inequality aversion theories that sweeping empirical claims should be avoided.decision theory, social dilemmas, inequality aversion, behavioral economics, experimental economics

Thermo-mechanical fatigue of cast aluminium alloys for engine applications under severe conditions

The increase in target performance of engines and hence the loading of their structural materials has dictated the need for more information about the behaviour of cast aluminium alloys under severe conditions up to 400°C. This study was therefore conducted in order to determine how different cooling rates, different pre-treatments and different alloying elements can improve the performance of cast aluminium (Al) alloys under thermo-mechanical fatigue (TMF) loading compared to a reference alloy and condition, AlSi6Cu4-T6. An existing TMF test rig was modified to allow an investigation of temperature gradients corresponding to those prevailing in real cylinder heads. The measured data were implemented in a Chaboche damage model and in an FEM tool in order to simulate low cycle fatigue (LCF) and TMF behaviour. These models provide a possibility to simulate LCF and TMF behaviour taking into account microstructural changes. On metallographic examination, a dependence of crack initiation on secondary dendrite arm spacing (SDAS) and on porosity was observed. Here, a smaller SDAS and a HIP modified microstructure led to a longer lifetime. Furthermore, clusters of brittle Si particles, decohesion or intermetallic phases were also found to initiate cracks. Stage I crack behaviour was seen at low strain amplitudes, where the crack propagates along the interface between the Al matrix and the intermetallic phases. Stage II behaviour was observed for higher strain amplitudes with crack propagation taking place along intermetallic phase boundaries such as Al2Cu, α-phase and β-phase or through pores. An increasing proportion of matrix cracks was observed for low strain amplitudes. Investigation of the decohesion behaviour revealed decohesion under high strain amplitudes and in areas with a high particle fracture volume attributable to high notch stresses. A refinement of the microstructure, particularly the particles, was found with increased Si content, associated with an increase in particle density. Following all TMF tests, an orientation of particles dependent on the loading conditions was observed, and this seemed to have had an influence on crack behaviour. A drift of stress was also found after long term high temperature exposure for strain amplitudes of 0.2%, attributed to creep

Anisotropic Zeeman Splitting in YbNi4P2

The electronic structure of heavy-fermion materials is highly renormalised at low temperatures with localised moments contributing to the electronic excitation spectrum via the Kondo effect. Thus, heavy-fermion materials are very susceptible to Lifshitz transitions due to the small effective Fermi energy arising on parts of the renormalised Fermi surface. Here, we study Lifshitz transitions that have been discovered in YbNi4P2 in high magnetic fields. We measure the angular dependence of the critical fields necessary to induce a number of Lifshitz transitions and find it to follow a simple Zeeman-shift model with anisotropic g-factor. This highlights the coherent nature of the heavy quasiparticles forming a renormalised Fermi surface. We extract information on the orientation of the Fermi surface parts giving rise to the Lifshitz transitions and we determine the anisotropy of the effective g-factor to be $\eta \approx 3.8$ in good agreement with the crystal field scheme of YbNi4P2.Comment: 10 pages, 5 figures, prepared for resubmission to SciPos