| 1. |
- Balkashin, O. P., et al.
(författare)
-
Nonstationary magnetization dynamics of point contacts with a single ferromagnetic film
- 2009
-
Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 35:8-9, s. 693-701
-
Tidskriftsartikel (refereegranskat)abstract
- The electric conductivity of point nanocontacts between 5, 10, and 100 nm thick ferromagnetic (F) cobalt films and a nonmagnetic (N) metal (copper or silver) needle is investigated. Two fundamentally different mechanisms for the formation of the response, signal to microwave irradiation have been observed for the first time. One mechanism is due to the effect of the rectification of high frequency ac current on the nonlinearity of the current-voltage characteristics due to the precession of the magnetization under the action of a constant transport current flowing through the contact. The second one is associated with the resonance excitation of the precession of the magnetization vector at the fundamental frequency and its harmonic by an external high-frequency field. The experimental results support a previous contention that a "surface spin valve" whose static and dynamic properties are similar to conventional F-1-N-F-2 spin valve [Nano Letters 7, 927 (2007)] is formed in the experimental F-N nanocontacts.
|
|
| 2. |
- Balkashin, O. P., et al.
(författare)
-
Spin dynamics in point contacts to single ferromagnetic films
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:9, s. 092419-1-092419-4
-
Tidskriftsartikel (refereegranskat)abstract
- Excitation of magnons or spin waves driven by nominally unpolarized transport currents in point contacts of normal and ferromagnetic metals is probed by irradiating the contacts with microwaves. Two characteristic dynamic effects are observed: a suppression of spin-wave nonlinearities in the point contact conductance by off-resonance microwave irradiation and a resonant stimulation of spin-wave peaks in the differential resistance of the nanocontacts by the microwave field. These observations provide direct evidence that the magnetoresistance peaks observed are due to gigahertz spin dynamics at the ferromagnetic interface driven by the spin transfer torque effect of the transport current.
|
|
| 3. |
- Ban, S., et al.
(författare)
-
Pattern storage and recognition using ferrofluids
- 2006
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 99:8
-
Tidskriftsartikel (refereegranskat)abstract
- An implementation of an associative memory based on a ferromagnetic nanocolloid is proposed. The design contains inductive input and output units for training the ferrofluid as well as sensors incorporated into the output units for performing recall. Using Monte Carlo simulations of the system we demonstrate the possibility of creating nanoparticle configurations that can serve to associate input/output pattern pairs.
|
|
| 4. |
- Iovan, A., et al.
(författare)
-
Diode effect in asymmetric double-tunnel barriers with single-metal nanoclusters
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 88:16
-
Tidskriftsartikel (refereegranskat)abstract
- Asymmetric double-tunnel barriers with the center electrode being a metal cluster in the quantum regime are studied. The zero dimensionality of the clusters used and the associated quantized energy spectra are manifest in well-defined steps in the current-voltage characteristic. Record high current rectification ratios of similar to 10(4) for tunneling through such clusters are demonstrated at room temperature. We are able to account for all of the experimentally observed features by modeling our double-barrier structures using a combination of discrete states and charging effects for tunneling through quantum dots.
|
|
| 5. |
- Iovan, A., et al.
(författare)
-
Rectification of current for tunneling through metallic nano-particles
- 2006
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 99:8
-
Tidskriftsartikel (refereegranskat)abstract
- Double tunnel barrier structures were obtained by using a scanning tunneling microscope and samples composed of metallic nanoparticles deposited onto an oxidized bottom electrode. The nanoparticles were formed by evaporating subpercolation thin metallic layers. Due to the small size of the particles their energy spectrum is discrete, which is evidenced by the measured quantized current-voltage characteristics. Current rectification ratios of 100-1000 for tunneling through such quantum dots are demonstrated at room temperature.
|
|
| 6. |
- Iovan, Adrian, et al.
(författare)
-
Spin diode based on Fe/MgO double tunnel junction
- 2008
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 8:3, s. 805-809
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a spin diode consisting of a semiconductor-free nanoscale Fe/MgO-based double tunnel junction. The device exhibits a near perfect spin-valve effect combined with a strong diode effect. The mechanism consistent with our data is resonant tunneling through discrete states in the middle ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent transparency. The observed magnetoresistance is a record high > 1000%, essentially making the structure an on/off spin switch. This, combined with the strong diode effect, similar to 100, demonstrates a new device principle, promising for memory and reprogrammable logic applications.
|
|
| 7. |
- Iovan, Adrian, et al.
(författare)
-
Tunneling spectroscopy of magnetic double barrier junctions
- 2007
-
Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 43:6, s. 2818-2820
-
Tidskriftsartikel (refereegranskat)abstract
- Scanning tunneling microscopy (STM) is used to study transport in magnetic double tunnel junctions (DTJs) formed using a fixed transparency barrier of a patterned tunnel junction (TJ), and a variable tunnel barrier between the top electrode of the patterned junction and the STM tip. A sufficiently thin top electrode has been predicted to result in a rectification of charge current through a DTJ when the two barriers have different transparency. Our measurements indeed show a high current rectification ratio for 3-nm-thick, continuous film top electrodes, which is observed for junctions with asymmetric tunnel barriers.
|
|
| 8. |
- Johansson, Jan, et al.
(författare)
-
Enhanced spin accumulation in superconductors
- 2006
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 99:8, s. 08M513-
-
Tidskriftsartikel (refereegranskat)abstract
- A lateral array of ferromagnetic tunnel junctions is used to inject and detect nonequilibrium quasiparticle spin distribution in a superconducting strip made of Al. The strip width and thickness are kept below the quasiparticle spin diffusion length in Al. Nonlocal measurements in multiple parallel and antiparallel magnetic states of the detectors are used to in situ determine the quasiparticle spin diffusion length. A very large increase in the spin accumulation in the superconducting state compared to that in the normal state is observed and is attributed to a diminishing of the quasiparticle population by the opening of the gap below the transition temperature.
|
|
| 9. |
- Kadigrobov, Anatoli M., 1937, et al.
(författare)
-
Joule heating and current-induced instabilities in magnetic nanocontacts
- 2006
-
Ingår i: Physical Review B. - 1098-0121 .- 1550-235X. ; 74:19
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the electrical current through a magnetic point contact in the limit of a strong inelastic scattering of electrons. In this limit local Joule heating of the contact region plays a decisive role in determining the transport properties of the point contact. We show that if an applied constant bias voltage exceeds a critical value, the stationary state of the system is unstable, and that periodic, nonharmonic oscillations in time of both the electrical current through the contact and the local temperature in the contact region develop spontaneously. Our estimations show that the necessary experimental conditions for observing such oscillations with characteristic frequencies in the range 10(8)-10(9) Hz can easily be met. We also show a possibility to manipulate upon the magnetization direction of a magnetic grain coupled through a point contact to a bulk ferromagnet by exciting the above-mentioned thermal-electric oscillations.
|
|
| 10. |
- Konovalenko, Alexander, et al.
(författare)
-
On the mechanism of hysteresis in conductance of point contacts to single ferromagnetic films
- 2007
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:9, s. 09A513-1-09A513-3
-
Tidskriftsartikel (refereegranskat)abstract
- Single nonmagnetic/ferromagnetic interfaces can exhibit magnetic excitations and hysteretic switching, provided that the current density traversing the interface is sufficiently high (greater than or similar to 10(8) A/cm(2)) and the flow regime is diffusive. We measure hysteretic switching in conductance induced by nominally unpolarized electron currents in nanocontacts to thin Co films and successfully model the effect for similar to 20 nm scale point contacts using micromagnetic simulations, which take into account an out of plane stress-induced magnetic anisotropy in the point contact region.
|
|
