A new method of measuring the dynamics of magnetization at arbitrary magnetic field is presented. It is illustrated by measuring the spin-lattice relaxation rate in paramagnetic Cdix Mn x Te in magnetic fields up to 25 T. At low fields, the spin-spin interaction of the Mn spins dominates the relaxation process; however, at high fields the relaxation of isolated spins can be observed. Among the spin clusters playing an important role as fast relaxation centers, exchange-coupled nearest-neighbor Mn pairs are identified, suggesting an important mixing of their states.PACS numbers: 75.20.-g, 76.30.Fc, 78.47.+p As a result of the presently available techniques, most of the experiments to study spin-lattice relaxation (SLR) are restricted to fields lower than a few tesla [1,2]. Unfortunately, at low magnetic fields, even for the most diluted magnetic systems, the interactions between spins of magnetic ions and also of uncontrollable impurities can strongly affect the relaxation [2], masking the isolatedspin behavior. However, at large enough magnetic fields, the mechansim of the relaxation becomes simpler since the interaction with the external magnetic field will be dominant, and the spin-spin interactions can be considered as negligible for the relaxation. Loosely speaking, the high magnetic field "purifies" the magnetic system, allowing studies of the isolated-spin relaxation. In addition, the relaxation rate for a multilevel system can be related directly to the transition probabilities between the levels at high magnetic fields only. This then allows the verification of possible theoretical models of SLR for such systems. Furthermore, one can expect that at high magnetic fields new relaxation processes could appear. For example, a simple theory [3] predicts that the relaxation with emission of two phonons could be important above about 20 T. This would manifest itself by a very strong magnetic field and a very weak temperature dependence of the SLR rates. Despite all these interesting questions, until now no detailed studies of spin-lattice relaxation in high magnetic fields and over a wide range of fields have been reported. In this work we developed a novel technique allowing studies of SLR in arbitrary fields. The technique has been illustrated by investigating SLR in the diluted magnetic semiconductor (DMS) Cdi-jcMn*-Te [4] for paramagnetic samples with compositions x between 0.002 and 0.05 [5] at magnetic fields B up to 24.5 T and at temperatures T between 2.6 and 10 K. We can conclude that at high fields single-spin relaxation is dominant for compositions x < 0.01. At lower fields the SLR is dominated by a channel given by the relaxation in spin clusters. The relaxation in exchange-coupled nearestneighbor (NN) pairs is clearly observed.The spin-lattice relaxation was measured with a timedomain magnetic spectrometer based on a pickup coil [6,7]. A pickup coil fixed around a paramagnetic sample with its axis parallel to an external magnetic field detects the externally induced changes of the longitudinal magne...
Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasi-classical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level m = EF /v 2 F .
Far-infrared magneto-optical investigations of shallow donors in epitaxial GaN layers on sapphire were carried out by means of Fourier transform spectrometry up to 23 T. From the splitting of the donor p states in a magnetic field, the cyclotron effective mass for conduction electrons was found to be m*=0.222 m0. A precise determination of the mass was made possible by the high quality of the spectra and by taking into account high magnetic field data above 12 T.
In this work, we have prepared a series of polydimethylsiloxane (PDMS) composites containing various graphene flakes loadings (0.02–2 wt%), and their broadband optical properties are being investigated. We demonstrate the tunability and evolution of transmittance and reflection spectra of the composites in a wide spectral range (0.4–200 μm) as a function of graphene content. Using these data we derive the broadband wavelength-dependent absorption coefficient (α) values. Our results show that α is roughly constant in the visible and IR ranges, and, surprisingly, is approximately one order of magnitude lower in the terahertz regime, suggesting different terahertz radiation scattering mechanism in our composite. Our material could be useful for applications in optical communication, sensing or ultrafast photonics.
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