Structural, magnetic, and magnetocaloric properties of Fe7Se8 single crystals

Abstract

The magnetocaloric effect has been studied in high quality single crystals of Fe7Se8 (3c type) grown by using Bridgman’s method. Magnetization and magnetocaloric effect measurements have been carried out in a magnetic field up to 5 T over the temperature range from 2 to 490 K. The spin reorientation transition from the easy c-axis to the easy c-plane, proceeding in an abrupt fashion, as a first-order phase transition, has been observed near the temperature TR ≈ 125 K. The magnetization curves in the vicinity of this transition were shown to have an S-shape with a clear hysteresis. The first order metamagnetic field induced transitions have been identified above and below TR. The conventional magnetocaloric effect related to the metamagnetic transitions has been found above TR, while below TR the inverse magnetocaloric effect was clearly seen. The existence of both kinds of magnetocaloric effect is important from the point of view of large rotating field entropy change in Fe7Se8 single crystals. The refrigeration capacity associated with a second order phase transition from the ferrimagnetic to the paramagnetic state at the Néel temperature TN ≈ 450 K was found to be weaker than that appearing near TR. The giant anisotropy of the magnetocaloric effect was related to the magnetic anisotropy of Fe7Se8 crystals. The one-ion model of the magnetocaloric effect has been developed and its predictions have been compared with experimental data.

Correlation between linear magnetostriction and magnetocaloric effect in the Fe7Se8 single crystals

“…Phase analysis and structure determination were performed by x-ray powder diffraction using a Siemens D500 diffractometer equipped with a semiconductor high-resolution Si:Li detector. It was found that the studied crystal is a single-phase material with a 3c structure and the following lattice constants: a=b=7.245 Å and c=17.67 Å (P3 1 21 space group) [9]. The chemical composition of the crystals was verified by scanning electron microscopy (SEM)/energy-dispersive x-ray spectroscopy (EDX) techniques using an X-MAX Silicon Drift Detector with the scanning electron microscope JEOL JSM-7600F.…”

“…The SR transition in the samples with the 3c structure occurs at∼125 K. The magnetic and magnetocaloric properties of these crystals have been presented in Refs. [9,10]. The magnetocaloric effect in Fe 7 Se 8 has attracted interest because of the existence of a normal MCE above the spin reorientation temperature T SRT for B || c and an inverse magnetocaloric effect below the T SRT for B ⊥ c [9,10].…”

“…[9,10]. The magnetocaloric effect in Fe 7 Se 8 has attracted interest because of the existence of a normal MCE above the spin reorientation temperature T SRT for B || c and an inverse magnetocaloric effect below the T SRT for B ⊥ c [9,10].…”

Two-Dimensional Room-Temperature Magnetic Nonstoichiometric Fe7Se8 Nanocrystals: Controllable Synthesis and Magnetic Behavior

“…In addition, Fe 7 Se 8 is one of the few systems possessing spin reorientation (the easy axis changes from the c-plane toward the c-axis at about 130 K), which is expected to have a large magnetocaloric effect in a wide temperature range. 13 However, the controllable synthesis of 2D nonstoichiometric Fe 7 Se 8 with accurate composition and high quality still faces great challenges. First, it is easy to introduce other impurities with different stoichiometric ratios, such as FeSe, Fe 3 Se 4 , and FeSe 2 .…”

“…Notably, Fe-based chalcogenides have received significant attention due to the intriguing discoveries of superconductivity and magnetism. − Fe 7 Se 8 was demonstrated to be ferrimagnetic with a high Néel temperature of 455 K, showing great application prospects in the field of RT spintronic devices. In addition, Fe 7 Se 8 is one of the few systems possessing spin reorientation (the easy axis changes from the c -plane toward the c -axis at about 130 K), which is expected to have a large magnetocaloric effect in a wide temperature range . However, the controllable synthesis of 2D nonstoichiometric Fe 7 Se 8 with accurate composition and high quality still faces great challenges.…”