Ferromagnetic/DMS hybrid structures: one- and zero-dimensional magnetic traps for quasiparticles (original) (raw)
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Zero- and one-dimensional magnetic traps for quasiparticles in diluted magnetic semiconductors
Physical Review B, 2005
We investigate the possibility of trapping quasi-particles possessing spin degree of freedom in hybrid structures. The hybrid system we are considering here is composed of a semi-magnetic quantum well placed a few nanometers below a ferromagnetic micromagnet. We are interested in two different micromagnet shapes: cylindrical (micro-disk) and rectangular geometry. We show that in the case of a micro-disk, the spin object is localized in all three directions and therefore zero-dimensional states are created, and in the case of an elongated rectangular micromagnet, the quasi-particles can move freely in one direction, hence one-dimensional states are formed. After calculating profiles of the magnetic field produced by the micromagnets, we analyze in detail the possible light absorption spectrum for different micromagnet thicknesses, and different distances between the micromagnet and the semimagnetic quantum well. We find that the discrete spectrum of the localized states can be detected via spatially-resolved low temperature optical measurement.
Optical response of a ferromagnetic/DMS hybrid structure
2004
We investigate the possibility of using local magnetic fields to produce one-dimensional traps in hybrid structures for any quasiparticle possessing spin degree of freedom. We consider a system composed of a diluted magnetic semiconductor quantum well buried below a micron-sized ferromagnetic island. Localized magnetic field is produced by a rectangular ferromagnet in close proximity of a single domain phase. We make quantitative predictions for the optical response of the system as a function of distance between the micromagnet and the quantum well, electronic g-factor, and thickness of the micromagnet.
Optical response of a ferromagnetic-diluted magnetic semiconductor hybrid structure
Applied Physics Letters, 2005
We investigate the possibility of using local magnetic fields to produce one-dimensional traps in hybrid structures for any quasiparticle possessing a spin degree of freedom. We consider a system composed of a diluted magnetic semiconductor quantum well buried below a micron-sized ferromagnetic island. A localized magnetic field is produced by a rectangular ferromagnet kept in a single domain phase. We make quantitative predictions for the optical response of the system as a function of distance between the micromagnet and the quantum well, electronic g factor, and thickness of the micromagnet.
Quantum wells based on magnetic-dipolar-mode oscillations in disk ferromagnetic particles
Europhysics Letters (EPL), 2003
We show that magnetic-dipolar-mode oscillations in a normally magnetized ferromagnetic disk have typical atomic properties like discrete-energy levels. Because of the discreteenergy eigenstates of such oscillations resulting from structural confinement, one can describe the oscillating system as a collective motion of quasiparticles-the light magnons. We calculate the energy levels in a magnetic quantum well and the effective masses of the light magnons.
Spin wave quantization in laterally confined magnetic structures (invited)
Journal of Applied Physics, 2001
An overview of the current status of the study of spin wave excitations in arrays of magnetic dots and wires is given. We describe both the status of theory and recent inelastic light scattering experiments addressing the most important issues; the quantization of localized spin waves due to the in-plane confinement of spin waves in elements, dipolar coupling between the quantized modes, and the localization of the modes within rectangular elements due to an inhomogeneous demagnetizing field.
Quantized spin wave modes in micron size magnetic disks
Journal of Applied Physics, 2000
We report on the observation of spin wave quantization in tangentially magnetized Ni 80 Fe 20 discs by means of Brillouin light scattering spectroscopy. For a large wave vector interval several discrete, dispersionless modes with a frequency splitting up to 2.5 GHz were observed. The modes are identified as being magnetostatic surface spin wave modes quantized by their lateral confinement in the disc. For the lowest modes dynamic magnetic dipolar coupling between the discs is found for a disc spacing of 0.1µm.
"Our work paves the way for the stabilization of novel quantum phases of matter that have no counterpart in thermodynamic equilibrium," commented Edoardo Baldini, assistant professor at The University of Texas at Austin. [35] Researchers have for the first time measured a fundamental property of magnets called magnon polarization—and in the process, are making progress towards building low-energy devices. [34]
Journal of Physics: Condensed Matter, 2004
The magnetic field dependences of the frequencies of standing spin-wave modes in a tangentially magnetized array of thin rectangular permalloy dots (800 × 550 nm) were measured experimentally by a Brillouin light scattering technique and calculated theoretically using an approximate size-dependent quantization of the spin-wavevector components in the dipole-exchange dispersion equation for spin waves propagating in a continuous magnetic film. It was found that the inhomogeneous internal bias magnetic field of the dot has a strong influence on the profiles of the lowest spin-wave standing modes. In addition, the dynamic magnetization distributions found for both longitudinally and transversely magnetized long magnetic stripes gives a good approximation for mode distributions in a rectangular dot magnetized along one of its inplane sides. An approximate analytic theory of exchange-dominated spin-wave modes, strongly localized along the dot edge that is perpendicular to the bias magnetic field, is developed. A good quantitative agreement with the results of the BLS experiment is found.
Quantized spin-wave modes in magnetic tunnel junction nanopillars
Physical Review B, 2010
We present an experimental and theoretical study of the magnetic field dependence of the mode frequency of thermally excited spin waves in rectangular shaped nanopillars of lateral sizes 60 × 100, 75 × 150, and 105 × 190 nm 2 , patterned from MgO-based magnetic tunnel junctions. The spin wave frequencies were measured using spectrally resolved electrical noise measurements. In all spectra, several independent quantized spin wave modes have been observed and could be identified as eigenexcitations of the free layer and of the synthetic antiferromagnet of the junction. Using a theoretical approach based on the diagonalization of the dynamical matrix of a system of three coupled, spatially confined magnetic layers, we have modeled the spectra for the smallest pillar and have extracted its material parameters. The magnetization and exchange stiffness constant of the CoFeB free layer are thereby found to be substantially reduced compared to the corresponding thin film values. Moreover, we could infer that the pinning of the magnetization at the lateral boundaries must be weak. Finally, the interlayer dipolar coupling between the free layer and the synthetic antiferromagnet causes mode anticrossings with gap openings up to 2 GHz. At low fields and in the larger pillars, there is clear evidence for strong non-uniformities of the layer magnetizations. In particular, at zero field the lowest mode is not the fundamental mode, but a mode most likely localized near the layer edges.
2010
vii viii Contents 2.3. Magnetic Properties of Artificial Domain Structures 26 2.4. Angle-Dependent Domain Wall Resistivity Measurements 33 2.5. Conclusions and Outlook 41 References 43 3 Fabrication of Magnetic Nanostructures by Electron Beam Induced Deposition 45 Masaki Takeguchi and Masayuki Shimojo Contents ix 4.5.2. Development for cell selective magnetic nanoparticles 81 4.6. Conclusions and Outlook References