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MA: Fachverband Magnetismus

MA 32: Postersession II: Spinstruct./Phase Trans. (1-10); Spinelectronics (11-15); Thin Films (16 - 36); Particles/Clusters (37-45); Multiferroics (46-54); Spindynamics/Spin Torque (55 - 76); Post Deadlines (77-79)

MA 32.8: Poster

Freitag, 29. Februar 2008, 11:15–14:00, Poster E

Study of EuCu₂(Ge_1−xSi_x)₂ across a quantum critical point — •Mahmoud A. Ahmida¹, Dirk Johrendt², Zakir Hossain³, Christoph Geibel⁴, and Mohsen M. Abd-Elmeguid¹ — ¹II Physikalisches Institut, Universität zu Köln, Köln, Germany — ²Department Chemie and Biochemie der Ludwig-Maximilians-Universität München, München, Germany — ³Department of Physics, Indian Institute of Technology, Kanpur, India — ⁴Max Planck Institut für Chemische Physik fester Stoffe, Dresden, Germany

The intermetallic series EuCu₂(Ge_1−xSi_x)₂ crystallizing in the tetragonal ThCr₂Si₂-type structure combines the antiferromagnetic (AF) compound EuCu₂Ge₂ (T_N=14 K) with the homogenous intermediate valent (IV) compound EuCu₂Si₂. Therefore, the system offers the opportunity to investigate the crossover from a magnetically ordered state to a nonmagnetic IV state through a quantum critical point (QCP) at x ≈ 0.65. To gain a microscopic insight into the change of the magnetic and valence states and their competition at the QCP, we have performed systematic ¹⁵¹Eu Mössbauer effect measurements on EuCu₂(Ge_1−xSi_x)₂ as a function of concentration (0 ≤ x ≤ 1) at different temperatures (300 to 4 K). The analysis of the results shows that the collapse of AF ordering for x > 0.50 is associated with a simultaneous sharp increase of the valence state of Eu towards the Eu⁺³state. It is shown that the simultaneous valence /magnetic phase transition across the QCP is of first-order.