Critical behavior in Ga-doped manganites La0.75(Sr,Ca)0.25Mn1−xGaxO3 (0≤x≤0.1)

The critical properties of perovskite manganite AMn_1−xGa_xO₃ (A=La_0.75Ca_0.08Sr_0.17, x=0, 0.05 and 0.1) at the ferromagnetic–paramagnetic transition have been analyzed. Experimental results revealed that all samples exhibit a second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various techniques such as modified Arrott plot, Kouvel–Fisher method, and critical magnetization isotherms M(T_C, H). The critical exponent values for the undoped compound were found to match well with those predicted for the three-dimensional Heisenberg model (β=355±0.007, γ=1.326±0.002, δ=4.90±0.01). While on non-magnetic Ga substitution it tends towards mean-field with long-range interaction. The mean-field model might be due to the random dilution of the Mn sublattice by non-magnetic ion Ga³⁺ and/or the development of the physical size of the clusters which enhance the dipole–dipole interaction.     

Position measurements in the de Broglie–Bohm interpretation of quantum mechanics

The de Broglie–Bohm interpretation of quantum mechanics assigns positions and trajectories to particles. We analyze the validity of a formula for the velocities of Bohmian particles which makes the analysis of these trajectories particularly simple. We apply it to particle detectors of four different types and show that the detectors of three of these types lead to “surrealistic trajectories”, i.e., leave a trace where the Bohmian particle was not present.