Magnetocaloric effect in Gd microwires

Abstract

In Gd microwires obtained by ultrafast cooling of the melt, a change in the magnetic entropy of 12 J/kg K was determined at a Curie temperature of 293 K in a magnetic field of 5 T. This value coincides with the change in the magnetic part of the entropy in bulk single-crystal samples in the same field. It has been found that in a strong magnetic field of 9 T, the temperature dependence of the entropy exhibits two maxima at temperatures of 292 and 312 K. The appearance of an additional entropy maximum in microstructured samples is caused by high mechanical microstresses retained in the sample after ultrafast cooling. Keywords: microwires, magnetic entropy, magnetoelastic anisotropy, Curie temperature.

Magnetic properties and magnetocaloric effect in Gd films and microwires

“…MgO with crystal-lattice orientation (100) was used as a substrate. The gadolinium microwires were produced by extraction of a hanging melt drop followed by superfast cooling on a water-cooled rotating disc [13].…”

“…Bulk gadolinium samples have significantly lower crystal anisotropy of magnetization that the anisotropy observed in films and microwires. In [13] authors reported a complicated temperature dependence of magnetic anisotropy found in gadolinium microwires, which contained two maxima of entropy that indicated a complicated-stressed state or a two-phase structure. A considerable MCE can be achieved in nano-and microstructures not only by placing the sample into a magnetic field or switching on the magnetic field, but by varying the permanent magnetic field orientation in relation to the sample.…”

“…This provides for avoiding the energy-intensive procedure of switching-on the field or moving the sample, allowing simply rotate it in the magnetic field of a permanent magnet. The comparison of MCE in microwires and films presented in [11][12][13] shows that with constant chemical composition and temperature modes of their preparation, micro-and nanostructures can demonstrate MCE with considerably different magnitude, which is caused by variations of the phase composition and internal microstresses. Indeed, the MCE estimate should also take into account the factor of demagnetization, which depends on the sample's shape, as it is convincingly demonstrated in [14,15].…”

Zinc selenide quantum dots as fluorescent labels for biomedical imaging

“…6 Zinc selenide is a direct band gap semiconductor material (E g $ 2.67 eV) displaying strong emission in the blue region of the visible spectrum, 7 which is known to exist in two different polymorphic forms namely, cubic zinc-blende and hexagonal wurtzite, where zinc-blende form is the thermodynamically stable phase. 8 The zinc-blende crystal structure remains stable up to 1,698 K, beyond which it undergoes a structural transformation (3C -2H transformation) into the wurtzite phase. 9 Zinc selenide exhibits both n-type and p-type conduction, characterized by the type of doping resulting from intrinsic defects.…”

“…In the family of II–VI selenides, the environmentally friendly compound zinc selenide (ZnSe) is hailed as one of the most promising materials thanks to its extensive applications in the field of optoelectronics 6 . Zinc selenide is a direct band gap semiconductor material (E g ~ 2.67 eV) displaying strong emission in the blue region of the visible spectrum, 7 which is known to exist in two different polymorphic forms namely, cubic zinc‐blende and hexagonal wurtzite, where zinc‐blende form is the thermodynamically stable phase 8 . The zinc‐blende crystal structure remains stable up to 1,698 K, beyond which it undergoes a structural transformation (3C ‐ 2H transformation) into the wurtzite phase 9 .…”