B. Lüthi

ESR absorption from the ground state in Haldane systems: theory and experiment

Abstract The ESR experiment provides us with much information on the ground and excited states of Haldane systems in a magnetic field. In this paper recent experimental results are reported on two typical Haldane materials, NENP and NINO. Then a theoretical interpretation is given on the spectrum; it is shown in particular how the ESR spectrum is related to the nature of the ground and excited states, which change with the applied magnetic field.

Magnetic resonances in powder-samples of quasi-one-dimensional anisotropic S = 1 spin systems

Abstract EPR experiments were performed on powder samples of the quasi-one-dimensional S = 1 spin systems NENC and TMNIN in the frequency range 55–400 GHz in magnetic fields up to 14 T. In both materials broad and asymmetric line shapes were observed pointing to a strong planar anisotropy. We interpreted the measured line shapes using a single-ion Hamiltonian. Transition matrix elements and occupation number of energy levels are taken into account in these calculations. In this way we obtain a good estimate for both the planar anisotropy D and the in-plane anisotropy E .

Low temperature thermal properties of two singlet ground state systems: Pr3Tl and PrSn3

Abstract Low temperature thermal properties of Pr 3 Tl and PrSn 3 , probing magnetoelastic interactions, are discussed. Emphasized is their behaviour at the magnetic phase transitions of these compounds.

Ultrasonic experiments in SrCu2(BO3)2 and NH4CuCl3 in magnetic fields up to 50 T

Abstract We present sound velocity data in high fields for the two plateau substances SrCu 2 (BO 3 ) 2 and NH 4 CuCl 3 . Pronounced sound velocity and attenuation anomalies are observed in the region between the magnetization plateaus. We interpret these as a resonant interaction between the sound wave mode and the soft magnetic excitations.

Elastic Properties of Superconducting Stannides: Yb3Rh4Sn13 and Ca3Rh4Sn13

We present an experimental investigation of the temperature and magnetic field dependence of the elastic constants in the two stannide compounds Yb3Rh4Sn13and Ca3Rh4Sn13. We find a small elastic softening of the c44mode of ca. 2% in the normal state. The temperature dependence of the various elastic modes are quite anomalous in the superconducting state. A comparison of our results is given with corresponding results of CeRu2, an amorphous superconductor and other amorphous materials.The authors present an experimental investigation of the temperature and magnetic field dependence of the elastic constants in the two stannide compounds Yb{sub 3}Rh{sub 4}Sn{sub 13} and Ca{sub 3}Rh{sub 4}Sn{sub 13} They find a small elastic softening of the C{sub 44} mode of ca. 2% in the normal state. The temperature dependence of the various elastic modes are quite anomalous in the superconducting state. A comparison of the results is given with corresponding results of CeRu{sub 2}, an amorphous superconductor and other amorphous materials.

Magnetic resonances in spin ladder systems (VO)2P2O7, SrCu2O3 and Sr2Cu3O5

Abstract We present magnetic resonance measurements on the S = 1 2 spin ladder systems (VO)2P2O7 (two legs), on the cuprates SrCu2O3 (two legs) and Sr2Cu3O5 (three legs). The measurements were performed in the frequency range 35–400 GHz at temperatures down to 1.5 K and in magnetic fields up to 14 T.

Haldane gap observation in TMNIN by electron spin resonance

Abstract Electron spin resonance (ESR) measurements on powder samples of the quasi-one-dimensional S = 1 Heisenberg antiferromagnet (CH 3 ) 4 NNi(NO 2 ) 3 (TMNIN) were performed for the first time in the frequency range 55–400 GHz in magnetic fields up to 14 T at temperatures down to 1.3 K. Resonance lines can be associated with transitions between excited states in the framework of a field theoretical model. The field dependence of the resonance modes points to a zero-field splitting of the triplet states at about 2.9 K due to a planar anisotropy. The temperature dependence of the line intensity confirms the existence of a Haldane gap in TMNIN with Δ / k B = 3.4 K .

Direct observation of the q = 0 spin-Peierls gap in CuGeO3 by high-field ESR

Abstract We present high-field Electron Spin Resonance (ESR) measurements on the spin-Peierls compound CuGeO3. We distinguish between two types of ESR transitions in the dimerized phase. They are associated with two energy gaps located at different points in the Brillouin zone. The renormalization of a q = 0 gap at E′g = 64 K as a function of temperature is measured.