J. J. Deng
Chinese Academy of Sciences
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Featured researches published by J. J. Deng.
Applied Physics Letters | 2009
Lungang Chen; Shouke Yan; Pingyong Xu; J. Lu; Wei Wang; J. J. Deng; Xuan Qian; Yang Ji; J. H. Zhao
We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature T-C can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x=20%. The temperature T-m, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below T-C, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than T-m.
Journal of Applied Physics | 2006
J. J. Deng; J. H. Zhao; J. F. Bi; Zhichuan Niu; Fm Yang; Xuebang Wu; Hua Zheng
Zinc-blende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. Compared with the typical thickness [2-3 ML (ML denotes monolayers)] of zb-CrSb grown directly on GaAs, the thickness of zb-CrSb grown on (In,Ga)As has been increased largely; the maximum can be up to similar to 9 ML. High-resolution cross sectional transmission electron microscopy images show that the zb-CrSb layer is combined with (In,Ga)As buffer layer without any dislocations at the interface
Applied Physics Letters | 2006
J. F. Bi; J. H. Zhao; J. J. Deng; Yonghui Zheng; S. S. Li; Xuebang Wu; Qi Jia
We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase.
Journal of Applied Physics | 2009
J. Lu; Hui-Yan Meng; J. J. Deng; P. Xu; Lungang Chen; J. H. Zhao; Q. J. Jia
Fe films with the different thicknesses were grown on c(4x4) reconstructed GaAs (001) surfaces at low temperature by molecular-beam epitaxy. Well-ordered bcc structural Fe epitaxial films are confirmed by x-ray diffraction patterns and high-resolution cross-sectional transmission electron microscopy images. A large lattice expansion perpendicular to the surface in Fe film is observed. In-plane uniaxial magnetic anisotropy is determined by the difference between magnetizing energy along [110] and [110] directions, and the constant of interfacial uniaxial magnetic anisotropy is calculated to be 1.02x10(-4) J m(-2). We also find that magnetic anisotropy is not obviously influenced after in situ annealing, but in-plane strain is completely changed.
Applied Physics Letters | 2007
Wei Wang; J. J. Deng; J. Lu; Baoyun Sun; J. H. Zhao
Zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs matrices are fabricated by in situ postgrowth annealing diluted magnetic semiconductor (Ga,Mn)As films with Mn concentration ranging from 2.6% to 8% at 650 degrees C. Magnetization measurements show that memory effect and slow magnetic relaxation, the typical characteristics of the spin-glass-like phase, occur below the blocking temperature of 45 K in samples with high Mn concentration, while for samples with low Mn concentration, ferromagnetic order remains up to 360 K. The behavior of low-temperature spin dynamics can be explained by the hierarchical model. (c) 2007 American Institute of Physics.
Journal of Applied Physics | 2006
Baoquan Sun; Desheng Jiang; Zheng Sun; Xuezhong Ruan; J. J. Deng; Jianhua Zhao; Yang Ji
Time-resolved Kerr rotation measurement in the (Ga,Mn)As diluted magnetic semiconductor allows direct observation of the dynamical properties of the spin system of the magnetic ions and the spin-polarized holes. Experimental results show that the magnetic ions can be aligned by the polarized holes, and the time scales of spin alignment and relaxation take place in tens and hundreds of picoseconds, respectively. The Larmor frequency and effective g factor obtained in the Voigt geometry show an unusual temperature dependence in the vicinity of the Curie temperature due to the exchange coupling between the photoexcited holes and magnetic ions. Such a spin coherent precession can be amplified or destructed by two sequential excitation pulses with circularly copolarized or oppositely polarized helicity, respectively.
Journal of Applied Physics | 2008
Guanxiang Du; Xiufeng Han; J. J. Deng; Wei Wang; Jianwen Zhao
We reported the all electronic demonstration of spin injection and detection in the trilayers with hybrid structure of CoFeB∕GaAs∕(Ga,Mn)As (metal/insulator semiconductor) by probing the magnetoresistance at low temperature from 1.8to30K. Tunneling magnetoresistance (TMR) ratios of 3.8%, 4.7%, 2.9%, and 1.4% at 1.8, 10, 20, and 30K, respectively, were observed. Bias dependence of both the junction resistance and TMR ratio was studied systematically. Vhalf at which TMR drops to half of its maximum is 6.3mV, being much smaller compared to that observed in (Ga,Mn)As∕ZnSe∕Fe and (Ga,Mn)As∕AlAs∕MnAs hybrid structures, indicating lower Fermi energy of (Ga,Mn)As.
Journal of Applied Physics | 2005
Chunping Jiang; Jian‐gao Zhao; J. J. Deng; Fm Yang; Zhichuan Niu; Xuebang Wu; Hou-Zhi Zheng
We have studied magnetic and transport properties of insulating and metallic (Ga,Mn)As layers before and after annealing. A dramatic increase of the ferromagnetic transition temperature T-C by postgrowth annealing has been realized in both insulating and metallic (Ga,Mn)As. The as-grown insulating (Ga,Mn)As can be turned into metallic by the low-temperature annealing. For all the metallic (Ga,Mn)As, a characteristic feature in the temperature dependence of sheet resistance appears around T-C. This phenomenon may provide a simple and more convenient method to determine the T-C of metallic (Ga,Mn)As compared with superconducting quantum interference device (SQUID) measurement. Moreover, the T-C of the metallic (Ga,Mn)As obtained by this way is in good agreement with that measured by a SQUID magnetometer
Journal of Applied Physics | 2009
Wei Wang; J. J. Deng; J. Lu; Baoyun Sun; Xuebang Wu; J. H. Zhao
We have fabricated a set of samples of zincblende Mn-rich Mn(Ga)As clusters embedded in GaAs matrices by annealing (Ga,Mn)As films with different nominal Mn content at 650 °C. For the samples with Mn content no more than 4.5%, the Curie temperature reaches nearly 360 K. However, when Mn content is higher than 5.4%, the samples exhibit a spin-glass-like behavior. We suggest that these different magnetic properties are caused by the competing result of dipolar and Ruderman–Kittel–Kasuya–Yosida interaction among clusters. The low-temperature spin dynamic behavior, especially the relaxation effect, shows the extreme creeping effect which is reflected by the time constant τ of ∼1011 s at 10 K. We explain this phenomenon by the hierarchical model based on the mean-field approach. We also explain the memory effect by the relationship between the correlation function and the susceptibility.
Journal of Applied Physics | 2009
Guanxiang Du; M. Ramesh Babu; Xiufeng Han; J. J. Deng; Wendong Wang; Jianwen Zhao; Jinke Tang
Tunneling magnetoresistance (TMR) in Ga(0.9)2Mn(0.08)As/Al-O/Co40Fe40B20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field vertical bar H vertical bar <= 2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 mu A. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented