Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTable-like magnetocaloric effect and enhanced refrigerant capacity in EuO1-{delta} thin films
98
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
An approach to adjusting the conduction band population for tuning the magnetic and magnetocaloric response of EuO1-{delta} thin films through control of oxygen vacancies ({delta} = 0, 0.025, and 0.09) is presented. The films each showed a paramagnetic to ferromagnetic transition around 65 K, with an additional magnetic ordering transition at higher temperatures in the oxygen deficient samples. All transitions are observed to be of second order. A maximum magnetic entropy change of 6.4 J/kg K over a field change of 2 T with a refrigerant capacity of 223 J/kg was found in the sample with {delta} = 0, and in all cases the refrigerant capacities of the thin films under study were found to exceed that reported for bulk EuO. Adjusting the oxygen content was shown to produce table-like magnetocaloric effects, desirable for ideal Ericsson-cycle magnetic refrigeration. These films are thus excellent candidates for small-scale magnetic cooling technology in the liquid nitrogen temperature range.
rate research
Read More
We report on a novel class of nanocrystalline/amorphous Gd$_3$Ni/Gd$_{65}$Ni$_{35}$ composite microwires, which was created directly by melt-extraction through controlled solidification. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the formation of a biphase nanocrystalline/amorphous structure in these wires. Magnetic and magnetocaloric experiments indicate the large magnetic entropy change (-$Delta$SM ~9.64 J/kg K) and the large refrigerant capacity (RC ~742.1 J/kg) around the Curie temperature of ~120 K for a field change of 5 T. These values are ~1.5 times larger relative to its bulk counterpart, and are superior to other candidate materials being considered for active magnetic refrigeration in the liquid nitrogen temperature range.
Mechanical control of magnetic properties in magnetostrictive thin films offers the unexplored opportunity to employ surface wave acoustics in such a way that acoustic triggers dynamic magnetic effects. The strain-induced modulation of the magnetic anisotropy can play the role of a high frequency varying effective magnetic field leading to ultrasonic tuning of electronic and magnetic properties of nanostructured materials, eventually integrated in semiconductor technology. Here, we report about the opportunity to employ surface acoustic waves to trigger magnetocaloric effect in MnAs(100nm)/GaAs(001) thin films. During the MnAs magnetostructural phase transition, in an interval range around room temperature (0{deg}C - 60{deg}C), ultrasonic waves (170 MHz) are strongly attenuated by the phase coexistence (up to 150 dB/cm). We show that the giant magnetocaloric effect of MnAs is responsible of the observed phenomenon. By a simple anelastic model we describe the temperature and the external magnetic field dependence of such a huge ultrasound attenuation. Strain-manipulation of the magnetocaloric effect could be a further interesting route for dynamic and static caloritronics and spintronics applications in semiconductor technology.
Neutron diffraction and magnetization measurements of the magneto refrigerant Mn1+yFe1-yP1-xGex reveal that the ferromagnetic and paramagnetic phases correspond to two very distinct crystal structures, with the magnetic entropy change as a function of magnetic field or temperature being directly controlled by the phase fraction of this first-order transition. By tuning the physical properties of this system we have achieved a maximum magnetic entropy change exceeding 74 J/Kg K for both increasing and decreasing field, more than twice the value of the previous record.
Investigating lateral electrical transport in p-type thin film chalcogenides is important to evaluate their potential for field-effect transistors (FETs) and phase-change memory applications. For instance, p-type FETs with sputtered materials at low temperature (<= 250 C) could play a role in flexible electronics or back-end-of-line (BEOL) silicon-compatible processes. Here, we explore lateral transport in chalcogenide films (Sb2Te3, Ge2Sb2Te5, Ge4Sb6Te7) and multilayers, with Hall measurements (in <= 50 nm thin films) and with p-type transistors (in <= 5 nm ultrathin films). The highest Hall mobilities are measured for Sb2Te3/GeTe superlattices (~18 cm2/V/s at room temperature), over 2-3x higher than the other films. In ultrathin p-type FETs with Ge2Sb2Te5, we achieve field-effect mobility up to ~5.5 cm2/V/s with current on/off ratio ~10000, the highest for Ge2Sb2Te5 transistors to date. We also explore process optimizations (e.g., AlOx capping layer, type of developer for lithography) and uncover their trade-offs towards the realization of p-type transistors with acceptable mobility and on/off current ratio. Our study provides essential insights into the optimization of electronic devices based on p-type chalcogenides.
Polycrystalline Heusler compounds Ni2Mn0.75Cu0.25Ga0.84Al0.16 with a martensitic transition between ferromagnetic phases and Ni2Mn0.70Cu0.30Ga0.84Al0.16 with a magnetostructural transformation were investigated by magnetization and thermal measurements, both as a function of temperature and magnetic field. The compound Ni2Mn0.75Cu0.25Ga0.84Al0.16 presents a large magnetocaloric effect among magnetically aligned structures and its causes are explored. In addition, Ni2Mn0.70Cu0.30Ga0.84Al0.16 shows very high, although irreversible, entropy and adiabatic temperature change at room temperature under a magnetic field change 0-1 T. Improved refrigerant capacity is also a highlight of the 30% Cu material when compared to similar Ni2MnGa-based alloys.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
