98 research outputs found
Current-induced magnetization reversal in a (Ga,Mn)As-based magnetic tunnel junction
We report current-induced magnetization reversal in a ferromagnetic
semiconductor-based magnetic tunnel junction (Ga,Mn)As/AlAs/(Ga,Mn)As prepared
by molecular beam epitaxy on a p-GaAs(001) substrate. A change in
magneto-resistance that is asymmetric with respect to the current direction is
found with the excitation current of 10^6 A/cm^2. Contributions of both
unpolarized and spin-polarized components are examined, and we conclude that
the partial magnetization reversal occurs in the (Ga,Mn)As layer of smaller
magnetization with the spin-polarized tunneling current of 10^5 A/cm^2.Comment: 13 pages, 3 figure
Coherency of the superconducting state: the muon spin rotation and ARPES studies of (BiPb)_2(SrLa)_2CuO_{6+\delta}
The superfluid density \rho_s in underdoped (T_c\simeq23K), optimally doped
(T_c\simeq35K) and overdoped (T_c\simeq29K) single crystalline
(BiPb)_2(SrLa)_2CuO_{6+\delta} samples was studied by means of muon-spin
rotation (\muSR). By combining the \muSR data with the results of ARPES
measurements on similar samples [Nature 457, 296 (2009)] good self-consistent
agreement is obtained between two techniques concerning the temperature and the
doping evolution of \rho_s.Comment: 4 pages, 3 figures
Giant magnetoelectric effect in an L 2ā-ordered CoāFeSi/Pb(Mgā/āNbā/ā)Oā-PbTiOā multiferroic heterostructure
We experimentally show a giant magnetoelectric (ME) effect at room temperature in an interfacial multiferroic heterostructure consisting of L2ā-ordered CoāFeSi and Pb(Mgā/āNbā/ā)Oā-PbTiOā (PMN-PT). Molecular beam epitaxy growth at 400 Ā°C enables us to obtain epitaxial and L2ā-ordered CoāFeSi films on PMN-PT(001). For the epitaxial CoāFeSi/PMN-PT heterostructure, the remanent magnetization state can be largely modulated by varying electric fields. We note that the room-temperature ME coupling coefficient (Ī±) is estimated to be 6.0-6.3 Ć 10 - ā¶ s/m, comparable to the highest Ī± value reported previously. Nonvolatile and repeatable magnetization changes in remanent states are also demonstrated. These results will pave the way for room-temperature electric-field control of the magnetization of half-metallic Heusler alloys in high-performance spintronic devices.T. Usami, S. Fujii, S. Yamada, Y. Shiratsuchi, R. Nakatani, and K. Hamaya, Appl. Phys. Lett. 118, 142402 (2021); https://doi.org/10.1063/5.004409
Effect of Fe atomic layers at the ferromagnet-semiconductor interface on temperature-dependent spin transport in semiconductors
Using artificially controlled ferromagnet (FM)-semiconductor (SC) interfaces, we study the decay of the nonlocal spin signals with increasing temperature in SC-based lateral spin-valve devices. When more than five atomic layers of Fe are inserted at the FM/SC interfaces, the temperature-dependent spin injection/detection efficiency (P inj /det) can be interpreted in terms of the T3/2 law, meaning a model of the thermally excited spin waves in the FM electrodes. For the FM/SC interfaces with the insufficient insertion of Fe atomic layers, on the other hand, the decay of P inj /det is more rapid than the T3/2 curve. Using magneto-optical Kerr effect measurements, we find that more than five atomic layers of Fe inserted between FM and SC enable us to enhance the ferromagnetic nature of the FM/SC heterointerfaces. Thus, the ferromagnetism in the ultra-thin FM layer just on top of SC is strongly related to the temperature-dependent nonlocal spin transport in SC-based lateral spin-valve devices. We propose that the sufficient ferromagnetism near the FM/SC interface is essential for high-performance FM-SC hybrid devices above room temperature.M. Yamada, Y. Shiratsuchi, H. Kambe, K. Kudo, S. Yamada, K. Sawano, R. Nakatani, and K. Hamaya, Journal of Applied Physics 129, 183901 (2021); https://doi.org/10.1063/5.0048321
Significant effect of interfacial spin moments in ferromagnet-semiconductor heterojunctions on spin transport in a semiconductor
Using controlled ferromagnet (FM) -semiconductor (SC) interfaces in SC-based lateral spin-valve (LSV) devices, we experimentally study the effect of interfacial spin moments in FM-SC heterojunctions on spin transport in SC. First-principles calculations predict that the spin moment of FM-SC junctions can be artificially reduced by inserting 3d transition metal V, Cr, or Cu atomic layers between FM and SC. When all-epitaxial FM-SC Schottky-tunnel contacts with a 0.4-0.5-nm-thick V, Cr, or Cu interfacial layer are formed, we find that the spin signals in FM-SC LSV devices are significantly decreased at 8 K. When we increase the interfacial spin moment by inserting an ā¼0.3-nm-thick Co layer between FM and SC, the spin signals at 8 K are significantly enhanced again. From these experiments, we conclude that the interfacial spin moments at FM-SC interfaces are one of the important factors to achieve large spin signals even in SC-based spintronic devices.T. Naito, R. Nishimura, M. Yamada, A. Masago, Y. Shiratsuchi, Y. Wagatsuma, K. Sawano, R. Nakatani, T. Oguchi, and K. Hamaya, Significant effect of interfacial spin moments in ferromagnet-semiconductor heterojunctions on spin transport in a semiconductor, Phys. Rev. B 105, 195308
The antiphase boundary in half-metallic Heusler alloy Co2Fe(Al,Si) : atomic structure, spin polarization reversal, and domain wall effects
Atomic resolution scanning transmission electron microscopy reveals the presence of an antiphase boundary in the half-metallic Co2Fe(Al,Si) full Heusler alloy. By employing the density functional theory calculations, we show that this defect leads to reversal of the sign of the spin-polarization in the vicinity of the defect. In addition, we show that this defect reduces the strength of the exchange interactions, without changing the ferromagnetic ordering across the boundary. Atomistic spin calculations predict that this effect reduces the width of the magnetic domain wall compared to that in the bulk
Topology and Homoclinic Trajectories of Discrete Dynamical Systems
We show that nontrivial homoclinic trajectories of a family of discrete,
nonautonomous, asymptotically hyperbolic systems parametrized by a circle
bifurcate from a stationary solution if the asymptotic stable bundles
Es(+{\infty}) and Es(-{\infty}) of the linearization at the stationary branch
are twisted in different ways.Comment: 19 pages, canceled the appendix (Properties of the index bundle) in
order to avoid any text overlap with arXiv:1005.207
Disentangling Cooper-pair formation above Tc from the pseudogap state in the cuprates
The discovery of the pseudogap in the cuprates created significant excitement
amongst physicists as it was believed to be a signature of pairing, in some
cases well above the room temperature. In this "pre-formed pairs" scenario, the
formation of pairs without quantum phase rigidity occurs below T*. These pairs
condense and develop phase coherence only below Tc. In contrast, several recent
experiments reported that the pseudogap and superconducting states are
characterized by two different energy scales, pointing to a scenario, where the
two compete. However a number of transport, magnetic, thermodynamic and
tunneling spectroscopy experiments consistently detect a signature of
phase-fluctuating superconductivity above leaving open the question of whether
the pseudogap is caused by pair formation or not. Here we report the discovery
of a spectroscopic signature of pair formation and demonstrate that in a region
of the phase diagram commonly referred to as the "pseudogap", two distinct
states coexist: one that persists to an intermediate temperature Tpair and a
second that extends up to T*. The first state is characterized by a doping
independent scaling behavior and is due to pairing above Tc, but significantly
below T*. The second state is the "proper" pseudogap - characterized by a
"checker board" pattern in STM images, the absence of pair formation, and is
likely linked to Mott physics of pristine CuO2 planes. Tpair has a universal
value around 130-150K even for materials with very different Tc, likely setting
limit on highest, attainable Tc in cuprates. The observed universal scaling
behavior with respect to Tpair indicates a breakdown of the classical picture
of phase fluctuations in the cuprates.Comment: 9 pages, 4 figure
Magnetic and structural depth profiles of Heusler alloy Co2FeAl0.5Si0.5 epitaxial films on Si(1ā1ā1)
The depth-resolved chemical structure and magnetic moment of Co2FeAl0.5Si0.5, thin films grown on Si(1 1 1) have been determined using x-ray and polarized neutron reflectometry. Bulk-like magnetization is retained across the majority of the film, but reduced moments are observed within 45ĖA of the surface and in a 25ĖA substrate-interface region. The reduced moment is related to compositional changes due to oxidation and diffusion, which are further quantified by elemental profiling using electron microscopy with electron energy loss spectroscopy. The accuracy of structural and magnetic depth-profiles obtained from simultaneous modeling is discussed using different approaches with different degree of constraints on the parameters. Our approach illustrates the challenges in fitting reflectometry data from these multi-component quaternary Heusler alloy thin films
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