This study presents a method of producing thick (i.e., in the $\ensuremath{\mu}\mathrm{m}$ range) polycrystalline $\mathrm{Gd}$ free-standing flexible films. Preparation is carried out by sputtering on silicon conventional substrates using tantalum as a buffer and capping layer. Magnetic and magnetocaloric properties show good agreement with data from high-purity bulk $\mathrm{Gd}$, and are not altered by substrate removal. Moreover, the free-standing film is flexible and all the relevant magnetic properties (i.e., Curie temperature ${T}_{c}$, saturation magnetization ${M}_{s}$, and isothermal entropy change $\mathrm{\ensuremath{\Delta}}S$) are preserved under bending (up to a $\ensuremath{\epsilon}=\ifmmode\pm\else\textpm\fi{}0.78\mathrm{%}$ strain over the two film sides). The technological opportunities heralded by availability of magnetocaloric flexible self-sustaining films are discussed in the conclusions with particular focus on energy-conversion applications (i.e., cooling and thermal energy harvesting). More precisely, the output-power upper bound of an thermal-energy harvester deploying a $\mathrm{Gd}$ flexible film with the reported properties is worked-out using a thermal switch model presented elsewhere. The calculations show a potential output able to supply the new generation of IoT wireless devices as well as small medical implants. The result moot $\mathrm{Gd}$ free-standing flexible films as a benchmark for a new generation of small high-throughput magnetocaloric energy-conversion devices.

Magnetocaloric Effect in Flexible, Free-Standing Gadolinium Thick Films for Energy Conversion Applications

The magnetocaloric effect (MCE) has made great success in very low temperature refrigeration, which is highly desirable for application to the extended higher temperature range. Here we report the giant enhancement of MCE in the metallic glass composite. The large magnetic refrigerant capacity (RC) up to 103 J·kg−1 is more than double the RC of the well-known crystalline magnetic refrigerant compound Gd5Si2Ge1.9Fe0.1 (357 J·kg−1) and MnFeP0.45As0.55 (390 J·kg−1)(containing either exorbitant-cost Ge or poisonous As). The full width at half maximum of the magnetic entropy change (ΔS
 m) peak almost spreads over the whole low-temperature range (from 303 to 30 K), which is five times wider than that of the Gd5Si2Ge1.9Fe0.1 and pure Gd. The maximum ΔSm approaches a nearly constant value in a wide temperature span over 100 K, and however, such a broad table-like region near room temperature has seldom been found in alloys and compounds. In combination with the intrinsic amorphous nature, the metallic glass composite may be potential for the ideal Ericsson-cycle magnetic refrigeration over a broad temperature range near room temperature.

Giant enhancement of magnetocaloric effect in metallic glass matrix composite

Structural features, magnetic properties and magnetocaloric effect of pure Gd ribbons prepared by melt spinning method were carefully analyzed. The X-ray data show that there is no change in the cell parameters for the samples prepared at different copper-wheel speed. Average size of nanocrystalline grains was close to 30 nm. As compared to the bulk Gd sample, the Curie temperature was the same in the case of the ribbons. From the magnetic isotherms, the magnetic entropy change was derived using the Maxwell relation follow the standard procedure. Its value was comparable with the value of the bulk Gd. Good mechanical properties of fabricated Gd ribbon and their flexibility can be useful for design of flexible refrigerating elements.

Magnetic and magnetocaloric properties of Gd melt-spun ribbons

We demonstrate a scheme to realize high-efficiency entanglement of two microwave fields in a dual opto-magnomechanical system. The magnon mode simultaneously couples with the microwave cavity mode and phonon mode via magnetic dipole interaction and magnetostrictive interaction, respectively. Meanwhile, the phonon mode couples with the optical cavity mode via radiation pressure. Each magnon mode and optical cavity mode adopts a strong red detuning driving field to activate the beam splitter interaction. Therefore, the entangled state generated by the injected two-mode squeezed light in optical cavities can be eventually transferred into two microwave cavities. A stationary entanglement E a 1 a 2 =0.54 is obtained when the input two-mode squeezed optical field has a squeezing parameter r = 1. The entanglement E a 1 a 2 increases as the squeezing parameter r increases, and it shows the flexible tunability of the system. Meanwhile, the entanglement survives up to an environmental temperature about 385 mK, which shows high robustness of the scheme. The proposed scheme provides a new mechanism to generate entangled microwave fields via magnons, which enables the degree of the prepared microwave entanglement to a more massive scale. Our result is useful for applications which require high entanglement of microwave fields like quantum radar, quantum navigation, quantum teleportation, quantum wireless fidelity (Wi-Fi) network, etc. 

High-efficiency entanglement of microwave fields in cavity opto-magnomechanical systems

Rapidly quenched non-strained nanocrystalline Gd ribbons: Structural features and magnetic properties

We have prepared Gd ribbons by melt-spinning. As-quenched Gd ribbon was then annealed at 750 °C for 2 h. The magnetic-entropy changes ( | Δ S M | ) in these ribbons are calculated. For annealed Gd ribbon, the values of | Δ S M | at low-field are large and the peaks in | Δ S M | - T plots are broad. The refrigerant capacity of this ribbon is significantly larger than that of bulk Gd metal. The influence of annealing on the | Δ S M | and the potential application of annealed Gd ribbons as a working material for magnetic refrigerants have been discussed.

The low-field magnetic entropy change in melt-spun and annealed Gd ribbons


 We theoretically explore the tunability of magnomechanically induced transparency (MMIT) phenomenon and fast-slow light effect in a hybrid cavity magnomechanical system in which a high-quality yttrium iron garnet (YIG) sphere and an atomic ensemble are placed inside a microwave cavity. In the probe output spectrum, we can observe magnon-induced transparency (MIT) and MMIT due to the photon-magnon and phonon-magnon couplings. We further investigate the effect of atomic ensemble on the absorption spectrum. The results show that better transparency can be obtained by choosing appropriate atomic ensemble parameters. We give an explicit explanation for the mechanism of the phenomenon of Fano resonance. Besides, we also discuss the phenomena of slow-light propagation. The maximum group delay increases significantly with the increase of the atom-cavity coupling strength, and the conversion between slow light and fast light can also be achieved by adjusting the atom-cavity coupling strength. These results may have a potential application for quantum information processing and high precision measurement.

Tunable magnomechanically induced transparency and fast-slow light in a hybrid cavity magnomechanical system

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The low-field magnetic entropy change in melt-spun and annealed Gd ribbons

Tunable magnomechanically induced transparency and fast-slow light in a hybrid cavity magnomechanical system