Spin-orientation phase transitions inNd2CuO4: A compound with n

Low-temperature specific heat ofNd2−xCexCuOHiền1, Duijn2, Colpa3 et al. 1998Phys. Rev. B152131View full textAdd to dashboardCite

“…VI we considered the nonconvergence of our computer program for small values ͑i.e., below about 4 T͒ of the applied field in the ab plane. We pointed out that this is consistent with the experimental findings of Cherny et al, 5 who observed a first-order phase transition at 4.4 T in magnetization measurements in applied fields along the a direction.…”

“…However, using the same computer program, we found solutions for fields above 4 T. Furthermore, we also found for zero field ͑using the computer program handling any value of the applied field along the c axis͒ a solution with 4 Nd-moment directions. These considerations lead to the conclusion that our calculations in some sense reproduce what was found experimentally by Cherny et al, 5 namely, a first-order phase transition at about 4.4 T in magnetization measurements at a temperature of 0.7 K, in fields applied along the a axis. At this field the low-field configuration with 4 Nd-moment directions abruptly changes into the high-field configuration with 2 Nd directions.…”

“…͑4.2͒ are the molecular fields at the Nd ion considered, due to the Nd-Cu and Nd-Nd two-ion interactions, respectively. By characteristic 2 we take, in accordance with other authors, 5,22 the molecular field B mol Nd-Cu as constant, in particular as independent of the temperature. The molecular field B mol Nd-Nd will be considered under characteristic 4 below.…”

“…The very low temperatures involved justify the approach of Adelmann et al that leads-for zero applied field only, see below-to a very elegant description by isolating just the essentials of the assumptions we made in the underlying paper. These authors proposed a splitting of the Nd 3ϩ groundstate doublet according to 4,5 and to our approach, the authors did not base their calculation on the fundamental assumption that at such a high applied field, in any part of the material the Cu moments orient themselves in such a way that B mol Nd-Cu and B appl are perpendicular.…”

Low-temperature magnetism ofNd2CuO4: An ultrasonic investigation

“…In between two consecutive phases, each three-layerspin unit, formed by one Cu 2+ layer sandwiched between two Nd 3+ layers, rotates as a whole by 90°in the ab plane, with the adjacent unit rotating in opposite direction. While the magnetic structure of Nd 2 CuO 4 is noncollinear in zero applied field, [11][12][13] the magnetic structure becomes collinear under a magnetic field of 4.4 and 0.75 T applied along the ͓100͔ and the ͓110͔ directions, respectively. 11 As shown in a thermal conductivity study of Nd 2 CuO 4 , these field-induced transitions are accompanied by the closure of a ϳ0.3 meV gap in an acoustic magnon branch at k = 0, leading to magnon heat transport at temperatures as high as 18 K. 14 Even though Nd 3+ spins are involved in these magnetic transitions, a spontaneous ordering of the Nd 3+ subsystem at low temperature, due to a Nd 3+ -Nd 3+ interaction, remains controversial.…”