Dresden 2011 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 23: CE: Quantum-Critical Phenomena 2

TT 23.3: Vortrag

Dienstag, 15. März 2011, 11:00–11:15, HSZ 105

Short range magnetic order close to a ferromagnetic quantum critical point in CeFePO — •Stefan Lausberg, Anton Jesche, Cornelius Krellner, Alexander Steppke, Luis Pedrero, Manuel Brando, Christoph Geibel, and Frank Steglich — Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany

The compound CeFeAs_1−xP_xO combines strong 3d and 4f correlation effects. At x = 0 two antiferromagnetic (AFM) transitions were found. Iron orders at T_{N, Fe} = 145 K and cerium at T_{N, Ce} = 3.7 K. Increasing the chemical pressure by phosphorus substitution leaves T_{N, Ce} almost unaffected while it shifts T_{N, Fe} towards lower temperatures until it vanishes above x = 0.35. Further increasing phosphorus content induces ferromagnetic (FM) order of cerium at T_c ≈ 9 K which is believed to suppress a superconducting state found in other iron pnictides when the iron AFM disappears. For x ≥ 0.6, T_c decreases and finally vanishes in CeFePO which was reported to be a paramagnetic heavy fermion system close to a FM instability. However, tiny differences in sample preparation lead to the onset of short range magnetic order.

In this contribution we present low-temperature magnetization, specific heat and ac-susceptibility measurements of a polycrystaline CeFePO sample. The ac-susceptibility shows a peak at T_f =620 mK which shifts towards higher temperatures by increasing the measuring frequency. We compare our results with the Kondo cluster glass CePd_1−xRh_x and discuss its properties in the frame of the quantum Griffiths phase scenario.