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TT: Fachverband Tiefe Temperaturen

TT 56: CE: Heavy Fermions

TT 56.6: Vortrag

Donnerstag, 17. März 2011, 18:00–18:15, HSZ 105

Magnetic field dependence of the antiferromagnetic order in YbCo₂Si₂ — •A. Haase¹, O. Stockert¹, N. Mufti¹, C. Krellner¹, J.-U. Hoffmann², A. Hoser², S. Capelli³, and C. Geibel¹ — ¹Max-Planck-Institut CPfS, Dresden, Germany — ²Helmholtzzentrum Berlin, Berlin, Germany — ³Institut Laue-Langevin, Grenoble, France

One of the model compounds to study quantum critical behaviour is YbRh₂Si₂, which orders antiferromagnetically at a very low T_N≈ 0.07 K. Due to the small ordered moment and the high neutron absorption of Rh the magnetic structure of YbRh₂Si₂ is still unknown. YbCo₂Si₂ with its body-centered tetragonal crystal structure is isoelectronic to YbRh₂Si₂ and serves as a reference system. YbCo₂Si₂ orders antiferromagnetically below T_N= 1.7 K with an additional first order transition at T_L= 0.9 K. This compound exhibits a complex magnetic (B, T) phase diagram for applied magnetic field and shows a pronounced basal plane anisotropy observed in magnetisation and magnetoresistance measurements. While at lowest temperature the magnetic order is commensurate with τ₁= (0.25 0.25 1), the magnetic structure becomes incommensurate above T_L with τ₂= (0.08 0.25 1). Using neutron diffraction we studied the magnetic structure in magnetic fields applied along [100], [110] and [001]. While in the commensurate phase no hysteresis was observed for all three directions of applied magnetic fields, a pronounced hysteresis of the intensity was detected in the incommensurate phase for fields along [100], which most likely can be attributed to different domain population.