The magnetization in a spin-Peierls material CuGe03 was measured by means of the Faraday rotation in ultrahigh magnetic fields up to 500 T. The experimental magnetization curve shows a nonlinear increase against the magnetic field which is a typical behavior of a one-dimensional quantum spin system. A distinct saturation of the magnetization was observed at 253 T, from which the exchange parameter is evaluated as 183 K. A large hysteresis of the magnetization was observed in the magnetic phase, whereas it was indiscernible in the uniform phase.
Electron paramagnetic resonance has been observed on CuGeO 3 in ultrahigh magnetic fields up to 180 T. The distinct exchange splitting is found between the two inequivalent Cu 2ϩ sites along the b axis. Analyzing the data on the basis of a simple two-spin model, we evaluated the interchain exchange coupling J b as ϳ0.9 meV. This value is a little smaller than J b ϳ1.0 meV obtained by neutron-scattering experiments.
Cyclotron resonance of two-dimensional holes in high-mobility GaAs-(Ga,Al)As heterojunctions with the growth directions (011), (111), (211), (311) and (100) has been measured at magnetic fields of around 35 T, corresponding to Landau level occupancies deep in the ultraquantum limit. A manipulation of the standard four-band Luttinger Hamiltonian has been used to show that the behaviour of the hole ground state is dominated by the leading field-dependent term in a power series expansion for the Landau level dispersion. The experimentally observed trend in measured effective mass with substrate orientation can therefore be qualitatively explained in terms of the variation of bulk hole mass with crystallographic direction.
The magnetization in S=1 one-dimensional Heisenberg antiferromagnets Ni(C2H8N2)2NO2(CiO4) (NENP) and CsNiCl3 was measured by means of the Faraday rotation in ultrahigh magnetic fields up to 150 T. A distinct saturation of the magnetization was observed in both samples. From the saturation field, the exchange coupling constants are evaluated as J=45.5 K and 25.8 K for NENP and CsNiCl3, respectively. The experimental magnetization curve is in good agreement with a theoretical curve for an S=1 one-dimensional Heisenberg antiferromagnet at finite temperatures.
The cyclotron resonance of very high-mobility holes in GaAs-(Ga, Al)As heterojunctions grown on (111), ( 311) and (100) substrates has been studied in high magnetic fields of up to 40 T. As the temperature is increased from ∼4 K to ∼20 K, the cyclotron resonance is found to shift to lower magnetic fields, the size of shift depending on the cyclotron frequency and the substrate orientation. These observations may be explained using the model of interacting hole subsystems developed by Cole et al .
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