Evidence for the homogeneous ferromagnetic phase in (Ga,Mn)(Bi,As) epitaxial layers from muon spin relaxation spectroscopy.

Ferromagnetic semiconductor thin layers of the quaternary (Ga,Mn)(Bi,As) and reference, ternary (Ga,Mn)As compounds, epitaxially grown under either compressive or tensile strain, have been characterized from a perspective of structural and magnetization homogeneity. The quality and composition of the layers have been confirmed by secondary-ion mass spectrometry (SIMS). A thorough evaluation of the magnetic properties as a function of temperature and applied magnetic field has been performed by means of SQUID magnetometry and low-energy muon spin relaxation (µSR) spectroscopy, which enables studying local (on the nanometer scale) magnetic properties of the layers. The results testify that the ferromagnetic order builds up almost homogeneously below the Curie temperature in the full volume fraction of both the (Ga,Mn)As and (Ga,Mn)(Bi,As) layers. Incorporation of a small amount of heavy Bi atoms into (Ga,Mn)As, which distinctly enhances the strength of spin-orbit coupling in the quaternary (Ga,Mn)(Bi,As) layers, does not deteriorate noticeably their magnetic properties.

Ising quantum Hall ferromagnet in magnetically doped quantum wells.

We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T(C) as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance "spikes" at T-->T(C) corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.

Pauli paramagnetism and Landau level crossing in a modulation doped CdMnTe/CdMgTe quantum well.

Electrical transport measurements are reported on a 2DEG in a CdMnTe quantum well structure. The amplitude of the Shubnikov-de Haas oscillations show a distinct beating pattern with nodes corresponding to coincidences between the spin splitting and a half integer multiple of the cyclotron energy. The observed pattern of nodes is a direct consequence of the large Pauli paramagnetism induced by the s-d exchange interaction between the spins of electronic states and the localized magnetic moments.