Inter-dot spin exchange interaction in coupled II–VI semiconductor quantum dots

Lee, S.,Dobrowolska, M.,Furdyna, J. K. WILEY-VCH Verlag 2006 Physica status solidi. PSS. B, Basic solid state p Vol.243 No.4

<P>We have performed polarization selective photoluminescence (PL) experiment on a series of self-assembled quantum dots (QDs) in the form of single- and double-QD layer systems. The double layers were formed from diluted magnetic semiconductor (DMS) (either CdMnSe or CdZnMnSe) and non-DMS (either CdSe or CdZnSe) layers, separated by non-DMS ZnSe barriers. The peaks from DMS and non-DMS QD layers are clearly resolved in the PL spectra taken at zero magnetic field. When a magnetic field is applied to the double layer QD (DLQD) system, the intensities of the circularly polarized PL peaks corresponding to the non-DMS (i.e., CdSe and CdZnSe) layers exhibit significant changes, reflecting correspondingly large changes in the degrees of spin polarization of the non-DMS QDs. This enhancement of spin polarization observed in the double-layer QD structures is interpreted in terms of anti-parallel spin interaction between carriers localized in the coupled QD pairs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Influence of RehaCom Therapy on the Improvement of Manual Skills in Multiple Sclerosis Subjects

Wioletta Pawlukowska,Natalia Dobrowolska,Aleksandra Szylinska,Dorota Koziarska,Agnieszka Meller,Iwona Rotter,Przemysław Nowacki 대한재활의학회 2020 Annals of Rehabilitation Medicine Vol.44 No.2

Objective To assess the influence of cognitive therapy, in combination with cognitive software, on manual dexterity in individuals with multiple sclerosis (MS). Methods The Nine-Hole Peg Test (NHPT) was used to establish the eligibility of individuals with MS for testing and to assess their upper limb performance. In addition to standard upper limb rehabilitation, 20 participants received RehaCom-based visual-motor therapy, administered three times a week in 20-minute routines. Results A significant relationship was found between the use of manual therapy that utilized the cognitive function platform and the improvement of the non-dominant hand (p=0.037). Compared to controls, the experimental group scored higher on the NHPT, when using the dominant hand (p=0.007). All members of the experimental group, aged ≤60 years, needed considerably less time to do the NHPT with the dominant hand (p=0.008). Conclusion Application of manual therapy using the cognitive function platform improves performance of the hand. However, further research is needed to analyze the correlation between cognitive function and motor performance in patients with MS.

Spin Phenomena of CdZnSe Self-assembled Quantum Dots Investigated by Magneto-photoluminescence

Yungjun Kim,M. Dobrowolska,J. K. Furdyna,이상훈 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.1

Magneto-photoluminescence (PL) experiments were carried out on a self-assembled CdZnSe/ZnSe quantum dot (QD) system. The intensities of the PL peak exhibited significant differences for the two circular polarizations when a magnetic field was applied. A simple two-level rate equation model, including the spin flip time τs and the exciton recombination time τr , was used to analyze the observed degree of the polarization in the polarization selective PL measurements. Specifically, the magnetic field dependence of the polarization was fitted by treating τs/τr as a fitting parameter in the model. The best fitting was obtained with the value of τs/τr ~ σ, indicating that the spin relaxation time is much longer than the exciton recombination time. Such polarization selective PL measurements were further performed at several different temperatures, which showed a systematic decrease in the degree of polarization with increasing temperature. Magneto-photoluminescence (PL) experiments were carried out on a self-assembled CdZnSe/ZnSe quantum dot (QD) system. The intensities of the PL peak exhibited significant differences for the two circular polarizations when a magnetic field was applied. A simple two-level rate equation model, including the spin flip time τs and the exciton recombination time τr , was used to analyze the observed degree of the polarization in the polarization selective PL measurements. Specifically, the magnetic field dependence of the polarization was fitted by treating τs/τr as a fitting parameter in the model. The best fitting was obtained with the value of τs/τr ~ σ, indicating that the spin relaxation time is much longer than the exciton recombination time. Such polarization selective PL measurements were further performed at several different temperatures, which showed a systematic decrease in the degree of polarization with increasing temperature.

Magneto-optical properties of CdSe-based magnetic semiconductor self-assembled quantum dots

Sanghoon Lee,M. Dobrowolska,J. K. Furdyna 한국진공학회 2007 한국진공학회 학술발표회초록집 Vol.16 No.2

Spin Relaxation Time of CdZnSe/ZnSe Self-Assembled Quantum Dots in a Magnetic Field

이상훈,J. K. Furdyna,M. Dobrowolska 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1

We have performed polarization-resolved magneto-photoluminescence (PL) experiments on a selfassembled CdZnSe quantum dot (QD) system to investigate the influence of an external magnetic field on the spin relaxation time of excitons in QDs. When the QDs are excited with circularly polarized light, the PL emissions at phonon resonance energies exhibit a noticeable degree of circular polarization (33 % and 6 % for 1-LO and 2-LO resonances, respectively) even at zero magnetic field while the PL at non-resonant positions shows zero circular polarization. The degree of polarization increases significantly when an external magnetic field is applied. Based on a simple two-level rate equation model, including a spin-flip time s and an exciton recombination time r, we are able to extract the magnetic field dependence of the ratio s/r. This ratio increases monotonically with the field and eventually becomes larger than 1, indicating that at high magnetic fields, spin relaxation times can exceed exciton recombination times.

Exchange Coupling in Magnetic Semiconductor Multilayers and Superlattices

Furdyna, J.K.,Leiner, J.,Liu, X.,Dobrowolska, M.,Lee, S.,Chung, J.-H.,Kirby, B.J. POLISH ACADEMY OF SCIENCES WARSAW 2012 Acta physica Polonica, A Vol.121 No.5

Magneto-Optical Properties of Non-Magnetic Semiconductor Quantum dot and Magnetic Quantum well Coupled Structures

이상훈,J. K. Furdyna,M. Dobrowolska 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3

The magneto-optical properties of quantum-dot (QD) and quantum-well (QW) coupled structures are investigated using magneto-photoluminescence (PL). The coupled system consists of a self-assembled non-magnetic CdSe quantum-dot layer and a 7-nm ZnCdMnSe diluted- magnetic-semiconductor (DMS) quantum well (QW) layer. We have observed two well-separated PL peaks, one corresponding to emission from the CdSe QD layer and the other to the emission for ZnCdMnSe QW layer. The temperature dependence of the PL intensity clearly demonstrates the characteristics of zero- and two-dimensional structures for the CdSe QDs and the ZnCdMnSe QW, respectively. The significant PL energy shift and intensity variation observed for the DMS QW in a magnetic field can be understood based on the giant Zeeman splitting of the band edges of the DMSs. Furthermore, we have observed a type-II transition between the conduction band of the DMS QW and the valence band of non-DMS QD, which enables us to determine the band alignment of the coupled systems.

Carrier relaxation processes in magnetic semiconductor quantum dot systems

이상훈,J. K. Furdyna,M. Dobrowolska 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.4

The energy relaxation process of dSe/ZnMnSe quantum dots (QDs) was investigated using polarization-selective magneto-photoluminescence (PL). Peaks from the Mn2+ internal transition, the CdSe QDs, and the ZnMnSe barrier were observed in the system. The CdSe QD peak was relatively weak while the intensity of the Mn2+ transition was strong in the spectrum taken at zero magnetic field. However, the peaks intensities changed significantly when a magnetic field was applied, and the situation became reversed (i.e., the CdSe QD peak become stronger than the peak due to the Mn2+ internal transition, specifically for + polarization). The opposite intensity behavior was observed in the peak from the Mn2+ ions and in the PL of the CdSe QDs and revealed that these two carrier capture centers competed with each other for carriers excited in the ZnMnSe barrier. The variation in the Mn2+ internal transition with the magnetic field was well described by using a model developed under an angular momentum selection rule. This suggests that competition between the two energy transfer processes in the CdSe/ZnMnSe QD system is responsible for the observed PL intensity behavior.

Manipulation of magnetization in GaMnAs films by spin-orbitinduced magnetic fields

이상엽,유태희,박슬기,최성훈,이학준,이상훈,X. Liu,J. K. Furdyna,M. Dobrowolska 한국물리학회 2017 Current Applied Physics Vol.17 No.5

We have investigated the effect of spin-orbit-induced (SOI) magnetic fields on magnetization switching in GaMnAs films. The sign of such SOI fields depends on the direction of the current flowing in the film, thus providing a handle for electrically manipulating magnetization in ferromagnetic GaMnAs films. Specifically, when an applied magnetic field is swept along the current direction, magnetization reversal occurs via rotations in opposite sense (i.e., clockwise (CW) or counterclockwise (CCW)) depending on the sign of the current, thus leading to opposite signs of the planar Hall resistance (PHR) measured on the film. The effect of SOI fields also manifests itself through hysteretic behavior of PHR for two opposite currents as a fixed magnetic field is rotated in the film plane. The width of the resulting hysteresis between two current directions then allows us to estimate the magnitude of the SOI field at current density of 1.0 105 A/cm2 as ~1.2 Oe in our GaMnAs film. Such switching of magnetization between two magnetic easy axes induced by switching the sign of an applied current provides a means of electronically controlling the value of film resistance (in this case of PHR), a process that can be exploited in spintronic devices.

Current induced magnetization switching in GaMnAsP film with Perpendicular Magnetic Anisotropy

Seongjin Park,Kyung Jae Lee,Phunvira Chongthanaphisut,Sanghoon Lee,X. Liu,M. Dobrowolska,J. K. Furdyna 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1

We have investigated spin-orbit torque (SOT) magnetization switching behavior of (Ga,Mn)(As,P) layer with perpendicular anisotropy. In order to study crystalline dependence of SOT magnetization switching, we have fabricated Hall devices along the [110] and the [110] directions, in which the Rashba-type and Dresselhaus-type spin-orbit fields are parallel and antiparallel to each other. We have adapted Hall effect measurements to monitor magnetization reversal process of the film. The Hall resistance (HR) measured with in-plane and out-of-plane magnetic field revealed that the (Ga,Mn)(As,P) film has out-of-plane magnetic easy axis. The SOT switching experiments was performed by scanning amplitude of current under in-plane bias field. In this experiment, we have observed opposite switching chirality for the [110] and the [110] directions, indicating opposite spin-orbit induced field for these two current directions. The results indicate that the Dresselhaus-type spin-orbit field is stronger than the Rashba-type field in a crystalline (Ga,Mn)(As,P) film.