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1.
ACS Nano ; 18(22): 14507-14513, 2024 Jun 04.
Artigo em Inglês | MEDLINE | ID: mdl-38758358

RESUMO

Nanoscopic magnetic domain walls (DWs), via their absence or presence, enable highly interesting binary data bits. The current-controlled, high-speed, synchronous motion of sequences of chiral DWs in magnetic nanoconduits induced by current pulses makes possible high-performance spintronic memory and logic devices. The closer the spacing between neighboring DWs in an individual conduit or nanowire, the higher the data density of the device, but at the same time, the more difficult it is to read the bits. Here, we show how the DW spacing can be dynamically varied to facilitate reading for otherwise closely packed bits. In the first method, the current density is increased in portions of the conduit that, thereby, locally speeds up the DWs, decompressing them and making them easier to read. In the second method, a localized bias current is used to compress and decompress the DW spacing. Both of these methods are demonstrated experimentally and validated by micromagnetic simulations. DW compression and decompression rates as high as 88% are shown. These methods can increase the density with which DWs can be packed in future DW-based spintronic devices by more than an order of magnitude.

2.
Nat Nanotechnol ; 17(11): 1183-1191, 2022 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-36203092

RESUMO

Of great promise are synthetic antiferromagnet-based racetrack devices in which chiral composite domain walls can be efficiently moved by current. However, overcoming the trade-off between energy efficiency and thermal stability remains a major challenge. Here we show that chiral domain walls in a synthetic antiferromagnet-ferromagnet lateral junction are highly stable against large magnetic fields, while the domain walls can be efficiently moved across the junction by current. Our approach takes advantage of field-induced global energy barriers in the unique energy landscape of the junction that are added to the local energy barrier. We demonstrate that thermal fluctuations are equivalent to the magnetic field effect, thereby, surprisingly, increasing the energy barrier and further stabilizing the domain wall in the junction at higher temperatures, which is in sharp contrast to ferromagnets or synthetic antiferromagnets. We find that the threshold current density can be further decreased by tilting the junction without affecting the high domain wall stability. Furthermore, we demonstrate that chiral domain walls can be robustly confined within a ferromagnet region sandwiched on both sides by synthetic antiferromagnets and yet can be readily injected into the synthetic antiferromagnet regions by current. Our findings break the aforementioned trade-off, thereby allowing for versatile domain-wall-based memory, and logic, and beyond.

3.
Nat Nanotechnol ; 17(10): 1065-1071, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-36138201

RESUMO

The fabrication of three-dimensional nanostructures is key to the development of next-generation nanoelectronic devices with a low device footprint. Magnetic racetrack memory encodes data in a series of magnetic domain walls that are moved by current pulses along magnetic nanowires. To date, most studies have focused on two-dimensional racetracks. Here we introduce a lift-off and transfer method to fabricate three-dimensional racetracks from freestanding magnetic heterostructures grown on a water-soluble sacrificial release layer. First, we create two-dimensional racetracks from freestanding films transferred onto sapphire substrates and show that they have nearly identical characteristics compared with the films before transfer. Second, we design three-dimensional racetracks by covering protrusions patterned on a sapphire wafer with freestanding magnetic heterostructures. We demonstrate current-induced domain-wall motion for synthetic antiferromagnetic three-dimensional racetracks with protrusions of up to 900 nm in height. Freestanding magnetic layers, as demonstrated here, may enable future spintronic devices with high packing density and low energy consumption.

4.
Adv Mater ; 34(23): e2109406, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35365874

RESUMO

The generation of spin currents from charge currents via the spin Hall effect (SHE) is of fundamental and technological interest. Here, some of the largest SHEs yet observed via extrinsic scattering are found in a large class of binary compounds formed from a 5d element and aluminum, with a giant spin Hall angle (SHA) of ≈1 in the compound Os22 Al78 . A critical composition of the 5d element is found at which there is a structural phase boundary between poorly and highly textured crystalline material, where the SHA exhibits its largest value. Furthermore, a systematic increase is found in the spin Hall conductivity (SHC) and SHA at this critical composition as the atomic number of the 5d element is systematically increased. This clearly shows that the SHE and SHC are derived from extrinsic scattering mechanisms related to the potential mismatch between the 5d element and Al. These studies show the importance of extrinsic mechanisms derived from potential mismatch as a route to obtaining large spin Hall angles with high technological impact. Indeed, it is demonstrated that a state-of-the-art racetrack device has a several-fold increased current-induced domain wall efficiency using these materials as compared to prior-art materials.

5.
ACS Nano ; 14(11): 15874-15883, 2020 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-33180460

RESUMO

Although recent experiments and theories have shown a variety of exotic transport properties of nonequilibrium quasiparticles (QPs) in superconductor (SC)-based devices with either Zeeman or exchange spin-splitting, how a QP interplays with magnon spin currents remains elusive. Here, using nonlocal magnon spin-transport devices where a singlet SC (Nb) on top of a ferrimagnetic insulator (Y3Fe5O12) serves as a magnon spin detector, we demonstrate that the conversion efficiency of magnon spin to QP charge via inverse spin-Hall effect (iSHE) in such an exchange-spin-split SC can be greatly enhanced by up to 3 orders of magnitude compared with that in the normal state, particularly when its interface superconducting gap matches the magnon spin accumulation. Through systematic measurements by varying the current density and SC thickness, we identify that superconducting coherence peaks and exchange spin-splitting of the QP density-of-states, yielding a larger spin excitation while retaining a modest QP charge-imbalance relaxation, are responsible for the giant QP iSHE. The latter exchange-field-modified QP relaxation is experimentally proved by spatially resolved measurements with varying the separation of electrical contacts on the spin-split Nb.

6.
Acta Biomed ; 90(1-S): 203-208, 2018 12 19.
Artigo em Inglês | MEDLINE | ID: mdl-30715026

RESUMO

BACKGROUND AND AIM OF THE WORK: the spontaneous and simultaneous rupture of both quadriceps tendons is uncommon and has rarely been reported in medical literature. The current case involves a 62-years old man with bilateral atraumatic complete quadriceps tendon rupture. Aim of this study is to provide a systematic review of this case and a literature review of similar cases. Methods: we reviewed and analyzed this patient's records. Initial x rays of both knees showed a bilateral patellar spur. Real time ultrasonography scan of both knees showed a complete tear of quadriceps. The repair has consisted on end to end Krackow sutures associated with bone suture to the proximal pole of the patella using patellar drill holes. We also researched the literature for bilateral simultaneous rupture of the quadriceps tendon. Results: The patient suffered only from seasonal asthma (receiving only inhaled corticosteroids) and he was overweight (BMI: 33,5), he did not do any type of sport, he was a biker. The patient was able to walk after 3 weeks with both knee cast. The patients had a 120° pain free range of motion in both knees 4 months after surgery. Conclusion: Simultaneous bilateral quadriceps tendon rupture is really very rare and these are generally reported as case presentation in the literature. This injury usually presents in middle aged people with a history of chronic illness. The general recommendation is to perform surgical intervention within 48-72 hours after injury.


Assuntos
Osteoartrite do Joelho/complicações , Osteófito/complicações , Patela , Traumatismos dos Tendões/etiologia , Acidentes por Quedas , Moldes Cirúrgicos , Terapia Combinada , Humanos , Imobilização , Masculino , Pessoa de Meia-Idade , Obesidade/complicações , Osteoartrite do Joelho/diagnóstico por imagem , Osteófito/diagnóstico por imagem , Patela/diagnóstico por imagem , Patela/cirurgia , Recuperação de Função Fisiológica , Ruptura Espontânea , Técnicas de Sutura , Traumatismos dos Tendões/diagnóstico por imagem , Traumatismos dos Tendões/cirurgia , Ultrassonografia
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