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Hexagonal manganites REMnO3 consist of layers of two-dimensional connected distorted MnO5 bipyramids separated by distorted layers of RE, leading to frustrated Mn3+–O2−–Mn3+ in-plane exchange paths (superexchange) and Mn3+–O2−–O2−–Mn3+ interplane exchange paths (super-superexchange). We report single-crystal diffraction experiments (RE=Ho,Er,Y) indicating magnetic 2D short-range order up to temperatures of T=150 K (TN∼74 K), and SQUID magnetization data (RE=Y) indicating short-range order up to at least 250 K. Fits of a model based on an extended mean-field theory to the single-crystal data show in-plane exchange about 3 orders of magnitude stronger than the interplane exchange, explaining the unusual strong deviation from the Curie–Weiss law of the SQUID magnetization data.

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This paper reports on experimental results obtained at the ISL-railgun facility EMA3 (muzzle velocity 0 2 km/s, applied energy per shot prim 1 MJ, = 3 m, regular cal. = 15 mm 30 mm, (multiple) metal fiber brush armatures) from 2001 to 2005. Several techniques with the aim of investigating contact performance up to 2 km/s were developed during this period. These techniques include: 1) quasi-segmented and wedge shaped rail configurations, which vary the width of the rail as a function of the rail length in order to maximize the performance of multiple brush armatures; 2) separating sabot technique, for which the latest experimental results and some calculated figures of merit based on a simple model are presented; and 3) new contact materials for solving the problem of gouging at very high contact transition velocities. Some experimental results obtained with brush armatures are presented. The paper concludes by presenting detailed results of a representative shot combining all of the mentioned techniques and clearly demonstrating their capacities. A lower limit of the contact transition velocity of 1800 m/s has been observed, increasing the previously observed value of 1100 m/s significantly.