The exchange bias effect is the physical cornerstone of applications, such as spin valves, ultra-high-density data storage, and magnetic tunnel junctions. This work studied the room temperature exchange bias effect by constructing a Ni50Mn38Sb12−xGax alloy system with coexisting martensitic phase structures. The study found that the exchange bias effect shows a non-monotonic change with the variation of Ga composition at 300 K, and an obvious room temperature exchange bias effect appears in the alloys with coexisting phase structures of 4O and L10, which is due to the strong exchange coupling between ferromagnetic and antiferromagnetic. Further research on the exchange bias effect and temperature shows that the blocking temperature is 420 K, and the exchange bias can stably exist in a temperature range of ∼200 K around room temperature. This work provides a method to engineer exchange bias effects at room temperature.
An interesting evolution of spin glass behaviors and the corresponding exchange bias effects were observed by quenching Ni50Mn42In3Sb5 Heusler alloys at different temperatures. When the alloy is quenched at 1173 K, it will freeze from antiferromagnetic to spin glass at low temperature under an external magnetic field, creating a giant exchange bias field up to 9063 Oe through the pinning effect. In another case, the superparamagnetic in alloys quenched at 473 K will transform to superspin glass after zero-field cooling at low temperatures instead. As a result, a spontaneous exchange bias effect up to 581 Oe can be achieved.
In this paper, crystallized core–shell Co@CoO nanocluster assembled thin films with different thicknesses were prepared by magnetron sputtering. A large zero-field-cooled exchange bias (ZEB) around 1280 Oe was obtained in the Co–CoO film with a thickness of 18 nm at 10 K. This phenomenon is mainly due to the formation of oriented Co@CoO core–shell nanoclusters (Co along the easy magnetization axis) in the amorphous Co–CoO matrix, thus exhibiting remnant magnetization, which is responsible for the ZEB. Moreover, the ZEB effect can be tuned by the varying film thickness. When the film thickness is decreased or increased, ZEB becomes weak, even vanishes. This indicates that we can select the desired value of ZEB via a simple control of the film thickness, which will benefit the applications of these thin films in the magnetic industry.
The exchange bias effect obtained after zero field cooling (ZEB) not only saves energy, but also makes the device easier to control and reduces the size of the device. In this work, ZEB effect under different measurement field is obtained in Ni50Mn37Ga13 alloy, further, combining the macroscopic magnetic test and phase field simulation, the microscopic magnetic states under different measurement fields are studied. Through phase field simulation, it is revealed that the density of ferromagnetic (FM)/antiferromagnetic (AFM) interface first expands and then shrinks with the increase of measurement field, which thus explains the optimum ZEB at an intermediate measurement field. This work reveals the important role of FM/AFM interface in the ZEB effect.
Sodium-ion batteries (SIBs) have potential as an energy storage system because they have similar electrochemical properties as lithium-ion batteries, abundant resource reserves, and extremely high safety performance. Compared with traditional graphite materials, conductive polymers are more suitable as an anode electrode material for SIBs. In this study, a simple and scalable approach has been used to synthesize p-toluenesulfonic acid-doped polypyrrole (p-TSA-PPy). The as-obtained material showed remarkable rate capacities and cyclability. At room temperature (25 °C), its discharge capacities could reach 185, 162, and 135 mAh g–1 under 10, 30, and 50 C rates after 250 cycles, respectively. More importantly, the capacity of the p-TSA-PPy could still be maintained at 120.5 mAh g–1 even at the 2000th cycle at 10 C. In addition, it achieves attractive electrochemical performance at different temperatures (0 and 50 °C).
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