Dresden 2006 – scientific programme

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TT: Tiefe Temperaturen

TT 19: Correlated Electrons: Low-dimensional Materials

TT 19.14: Talk

Tuesday, March 28, 2006, 17:30–17:45, HSZ 301

Magnetically driven microwave absorption in La₁Sr₁MnO₄: Pulsed magnetic fieldstudies — •R. Klingeler^1,2, V. Kataev¹, U. Schaufuß¹, B. Büchner¹, P. Reutler^1,3, A. Revcolevschi³, M. Goiran², H. Rakoto², J.M. Broto², and B. Raquet² — ¹IFW Dresden, Germany — ²LNCMP Toulouse, France — ³UniversitéParis-Sud, France

Spin degrees of freedom are expected to dominate the magnetism in layered hole-free La₁Sr₁MnO₄ as the orbital momentum of the Mn ions is quenched by the anisotropic crystal field. Surprisingly, our thermal expansion and NEXAFS data indicate that orbitals are still relevant. There is a temperature driven reorientation of the orbital states. Recent inelastic neutron scattering (INS) data reveal a large spin gap of ∼2.2 THz and two in-gap excitations at 0.8 THz and 1.7 THz in the antiferromagnetically (AF) ordered ground state. The origin of the large anisotropy and the in-gap excitations is unclear. Here we report high frequency electron spin resonance, magnetization and electrical conductivity measurements in magnetic fields up to 60 T. In the AF ordered state we observe a surprisingly strong absorption of sub-Terahertz electromagnetic radiation in fields above 15 T. In the DC limit conductivity measurements yield a significant negative magnetoresistance R(H) as well. However, there are no anomalies in R(H) as well as in the magnetization M(H) in the field range where strong microwave absorption is observed. At still larger fields M(H) reveals the anomaly which can be associated with the lower in-gap spin excitation found in the INS. We discuss our results in terms of an unusual interplay between structure, orbitals and spins.