Breaking the geometric magnetic frustration in controlled off-stoichiometric LuMn1+zO3+δ compounds.

This study explores controlled off-stoichiometric LuMn1+zO3+δ (|z| < 0.1) compounds, intended to retain the utter LuMnO3 intrinsic hexagonal symmetry and ferroelectric properties. X-ray powder diffraction measurements evidenced a single phase P63cm structure. Thermo-gravimetric experiments show a narrow impact of oxygen vacancies while a distinguishable gas exchange at ∼700 K, a surprisingly lower temperature when compared to perovskite systems. A comparison of different nominal ceramics revealed pertinent structural and magnetic property variations owing to subtle self-doping effects. Deviations from the archetypal antiferromagnetic state were detected below ∼90 K suggesting local rearrangements of the nominal Mn(3+) ions matrix, breaking the ideal geometrical spin frustration, leading to a non-compensated magnetic structure.

Heat-capacity measurements on small samples: the hybrid method.

A newly developed method is presented for measuring heat capacities on small samples, particularly where thermal isolation is not sufficient for the use of the traditional semiadiabatic heat-pulse technique. This "hybrid technique" is a modification of this heat-pulse method in case the temperature drift of the sample after the heat pulse is not linear but exponential. Deliberate extrapolations of these exponential drift curves, dependent on the evaluated relaxation time, yield reliable results for the temperature steps. The method is faster than the traditional relaxation method, and by comparing with the values published by the National Bureau of Standards (NBS) on copper, the accuracy is shown to be of the order of 1%.