Subrata Ghosh

Bio: Subrata Ghosh is an academic researcher from S.N. Bose National Centre for Basic Sciences. The author has contributed to research in topics: Magnetic refrigeration & Ferromagnetism. The author has an hindex of 4, co-authored 8 publications receiving 49 citations.

Giant Room-Temperature Magnetocaloric Effect Across the Magnetostructural Transition in ( Mn Ni Si ) 1 − x ( Fe Co Ga ) x Alloys

Abstract: Magnetic and structural transitions are observed to coincide at around room temperature in transition-metal-based $(\mathrm{Mn}\mathrm{Ni}\mathrm{Si}{)}_{1\text{\ensuremath{-}}x}(\mathrm{Fe}\mathrm{Co}\mathrm{Ga}{)}_{x}$ (x = 0.15 and 0.16) alloys, which leads to a coupled first-order magnetostructural transition (MST) from paramagnetic hexagonal to ferromagnetic orthorhombic structure, and, as a result, a giant magnetocaloric effect is observed in these alloys. With subsequent doping for x = 0.17, the MST decouples into two separate transitions, structural and magnetic, although the transitions couple upon enhancing the applied magnetic field. The alloys with x = 0.15, 0.16, and 0.17 are found to exhibit isothermal magnetic entropy changes ($|\mathrm{\ensuremath{\Delta}}{S}_{M}|$) as large as about $25\phantom{\rule{0.1em}{0ex}}\mathrm{J}\phantom{\rule{0.1em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 323 K, about $31.1\phantom{\rule{0.1em}{0ex}}\mathrm{J}\phantom{\rule{0.1em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 281 K, and about $23.8\phantom{\rule{0.1em}{0ex}}\mathrm{J}\phantom{\rule{0.1em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 213 K, respectively, due to a field change of \ensuremath{\Delta}H = 50 kOe. These low-cost materials may be considered as promising candidates for magnetic refrigeration around room temperature due to their giant magnetocaloric properties, with significantly large relative cooling power (RCP = 191.8, 209.6, and 139.2 J/kg, respectively, for x = 0.15, 0.16, and 0.17 due to \ensuremath{\Delta}H = 50 kOe).

Realization of multifunctional shape-memory ferromagnets in all-d-metal Heusler phases

Abstract: Heusler ferromagnetic shape-memory alloys (FSMAs) normally consist of transition-group d-metals and main-group p-elements. Here, we report the realization of FSMAs in Heusler phases that completely consist of d metals. By introducing the d-metal Ti into NiMn alloys, cubic B2-type Heusler phase is obtained and the martensitic transformation temperature is decreased efficiently. Strong ferromagnetism is established by further doping Co atoms into the B2-type antiferromagnetic Ni-Mn-Ti austenite. Based on the magnetic-field-induced martensitic transformations, collective multifunctional properties are observed in Ni(Co)-Mn-Ti alloys. The d metals not only facilitate the formation of B2-type Heusler phases, but also establish strong ferromagnetic coupling and offer the possibility to tune the martensitic transformation.

Mastering hysteresis in magnetocaloric materials

Abstract: Hysteresis is more than just an interesting oddity, which occurs in materials with a first-order transition. It is a real obstacle on the path from existing lab-scale prototypes of magnetic refrigerators towards commercialization of this potentially disruptive cooling technology. Indeed, the reversibility of the magnetocaloric effect, being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and therefore it is necessary to understand the mechanisms causing hysteresis and to find solutions how to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, we discuss fundamental aspects, which can contribute to thermal hysteresis and we are developing strategies for at least partially overcoming the hysteresis problem in some selected classes of magnetocaloric materials with large application potential. Doing so, we refer to the most relevant classes of magnetic refrigerants La-Fe-Si-, Heusler- and Fe2P-type compounds.

Enhanced magnetocaloric performances and tunable martensitic transformation in Ni35Co15Mn35−xFexTi15 all-d-metal Heusler alloys by chemical and physical pressures

Abstract: The solid-state magnetic cooling (MC) method based on the magnetocaloric effect (MCE) is recognized as an environmentally friendly and high-energy-efficiency technology. The search or design of suitable magnetic materials with large MCEs is one of the main targets at present. In this work, we apply the chemical and hydrostatic pressures in the Ni35Co15Mn35−xFexTi15 all-d-metal Heusler alloys and systematically investigate their crystal structures, phases, and magnetocaloric performances experimentally and theoretically. All the alloys are found to crystallize in an ordered B2-type structure at room temperature and the atoms of Fe are confirmed to all occupy at sites Mn(B). The total magnetic moments decrease gradually with increasing Fe content and decreasing of volume as well. The martensitic transformation temperature decreases with the increase of Fe content, whereas increases with increasing hydrostatic pressure. Moreover, obviously enhanced magnetocaloric performances can also be obtained by applied pressures. The maximum values of magnetic entropy change and refrigeration capacity are as high as 15.61(24.20) J (kg K)−1 and 109.91(347.26) J kg−1 with ΔH = 20(50) kOe, respectively. These magnetocaloric performances are superior to most of the recently reported famous materials, indicating the potential application for active MC.