The recent discovery of diffuse, VHE γ radiation from the Galactic center ridge by the H.E.S.S. telescope allow for the first time the direct determination of parameters of galactic cosmic ray propagation models. In this paper we show that the diffuse γ-radiation near the Galactic center may be explained by the interaction of VHE cosmic ray (CR) protons with the interstellar gas located in several giant molecular clouds leading to a measurement of the cosmic ray diffusion coefficient for the galactic center region of κ = 1.3 kpc 2 Myr −1 for a mean proton energy of ∼ 3 TeV, if we assume that the CR protons originated from a supernova event (Sgr A East), which took off about 10 kyr ago. This value of κ is ∼ 5 to 10 times smaller than the locally measured value.

Previous investigations into the physical properties of PrSi have shown this compound to order ferromagnetically at 54 K. However, the magnetic ground state has not yet been determined unambiguously. PrSi crystallizes in the orthorhombic FeB-type structure. Typically, the crystalline electric field (CEF) would uplift the degeneracy of the J=4 Pr3+ free-ion ground state multiplet, yielding nine (normally non-magnetic) singlets. It is known that magnetic order in such systems may be established via the admixture of two singlets into a doublet state, analogous to TmNi, which crystallizes in the same structure. From symmetry considerations, collinear ferromagnetically ordered moments should lie parallel to the crystallographic b-axis. However, neutron diffraction experiments have shown that the easy magnetic axis lies in the ac-plane. This is the first suggestion that the ground state in PrSi is not determined by the CEF alone. Here, we investigate the ground state properties of PrSi by analyzing its specific heat. A Schottky contribution associated with the thermal population of CEF-split energy levels is absent from the 4f-electron contribution to the specific heat and the magnetic configurational entropy points to a full nine-fold degenerate J=4 multiplet magnetic ground state. The strongest evidence for such a ground state is found when the magnetocaloric effect (MCE) in this system is considered. Furthermore, the MCE indicates the presence of a significant higher order exchange term in the magnetic Hamiltonian.

The temperature dependence of exchange bias properties are studied in polycrystalline BiFeO 3 /Ni 81 Fe 19 bilayers, for different BiFeO 3 thicknesses. Using a field cooling protocol, a non-monotonic behavior of the exchange bias field is shown in the exchange-biased bilayers. Another thermal protocol, the Soeya protocol, related to the BiFeO 3 thermal activation energies was carried out and reveals a two-step evolution of the exchange bias field. The results of these two different protocols are similar to the ones obtained for measurements previously reported on epitaxial BiFeO 3 , indicating a driving mechanism independent of the long-range crystalline arrangement (i.e., epitaxial or polycrystalline). An intrinsic property of BiFeO 3 is proposed as being the driving mechanism for the thermal dependent magnetization reversal: the canting of the BiFeO 3 spins leading to a biquadratic contribution to the exchange coupling. The temperature dependence of the magnetization reversal angular behavior agrees with the presence of such a biquadratic contribution for exchange biased bilayers studied here.

The compound NdAuGe was investigated by means of electrical resistivity, ρ(T), magnetic susceptibility, χ(T), magnetization, σ(μ0H), and specific heat, Cp(T), measurements. Powder X-ray diffraction studies confirm a hexagonal LiGaGe-type structure with space group P63mc (No. 186). ρ(T) data show normal metallic behaviour and a tendency toward saturation at higher temperatures. The low temperature ρ(T) data indicate a phase transition around 3.8 K. The low field dc χ(T) data show an antiferromagnetic anomaly associated with a Néel temperature at TN = 3.7 K close to the phase transition observed in ρ(T) results. At higher temperatures, χ(T) follows the paramagnetic Curie-Weiss behaviour with an effective magnetic moment μeff=3.546(4) μB and a paramagnetic Weiss temperature of θp=−6.1(4) K. The value obtained for μeff is close to the value of 3.62 μB expected for the free Nd3+-ion. σ(μ0H) shows a linear behaviour with applied field up to 3 T with an evidence of metamagnetic behaviour above 3 T. Cp(T) confirms the magnetic phase transition at TN = 3.4 K. The 4f-electron specific heat indicates a Schottky-type anomaly around 16.5 K with energy splitting Δ1=25.8(4) K and Δ2=50.7(4) K of the Nd3+ (J = 9/2) multiplet, that are associated with, respectively, the first and second excited states of the Nd3+-ion.

PrNiGe2 crystallizes in the orthorhombic CeNiSi2-type crystal structure and is known to order ferromagnetically below 13 K. The emergence of ferromagnetic order has been understood in terms of a crystalline electric field (CEF) Hamiltonian dominated by O0n-Stevens operator equivalents. However, a recent calculation points out that the O22-terms are important in this system. Here a study of the magnetocaloric effect (MCE) of PrNiGe2 is presented. The aim of the study is to investigate the origin of long range ferromagnetic order given the presence of the above-mentioned CEF. We find that the interplay between a dominant CEF-energy scale and a weaker exchange interaction results in the formation of a ferromagnetic ground state in this system.