Phase transitions and corresponding magnetic entropy changes in Ni2Mn0.75Cu0.25−xCoxGa Heusler alloys

Abstract

Articles you may be interested inLarge reversible entropy change at the inverse magnetocaloric effect in Ni-Co-Mn-Ga-In magnetic shape memory alloys Detailed studies of room temperature crystal structures, phase transitions, and related magnetic entropy changes ͑⌬S m ͒ in shape memory alloys Ni 2 Mn 0.75 Cu 0.25−x Co x Ga ͑x = 0.0, 0.01, 0.02, 0.025 0.03, 0.05͒ have been carried out by x-ray diffraction, magnetization, and thermal expansion measurements in magnetic fields of up to 5 T and in a temperature interval of 5-400 K. The high temperature austenitic cubic phase passes through a magnetic transition to ferromagnetic state and a structural transition to martensitic phase at the same temperature for all samples of the Ni 2 Mn 0.75 Cu 0.25−x Co x Ga system. The first order magnetostructural transition temperature increases from 308 to 345 K with increasing Co concentration. All of the alloys in the Ni 2 Mn 0.75 Cu 0.25−x Co x Ga system were found to possess large magnetic entropy changes. The maxima in the magnetic entropy changes ranged from ⌬S m max = −48 J / kg K to −64 J / kg K in a temperature range of 308-345 K.

Origin of magnetic interactions and their influence on the structural properties of Ni2MnGa and related compounds

“…Being magnetic, these materials can show a strong coupling between structural and magnetic transitions [2][3][4][5][6][7][8]11 which is very appealing for a wealth of different technological applications. In fact, Heusler alloys have been studied quite extensively for their magneto-caloric [13][14][15][16][17] and magnetomechanical [9][10][11][12]18 properties and more recently for their applications in energy conversion 19 .…”

“…In fact, Heusler alloys have been studied 1 Present address: Leibniz Institute of Solid State and Materials Research, Dresden, Germany. quite extensively for their magneto-caloric [13][14][15][16][17] and magneto-mechanical [9][10][11][12]18] properties and more recently for their applications in energy conversion [19].…”

“…Figure13. Comparison of the total ground state energy and the magnetic energy per unit cell in the GGA + U.…”

The structural and magnetic properties of Ni2Mn1−xBxGa Heusler alloys

“…The coexistence of T M and T C results in a single magnetocrystalline phase transition where a giant magnetic entropy change is observed [12]. Most studies are carried out on the ternary Ni-Mn-Ga alloys and recently the amount of research on the quaternary Ni-Mn-Gabased alloys has grown [13][14][15][16][17][18]. The substitution of Mn by Fe in Ni 2 MnGa-based compounds causes a decrease of T M and an increase of T C [14].…”

Magnetocaloric and magnetic properties of Ni2Mn1−xCuxGa Heusler alloys: An insight from the direct measurements and ab initio and Monte Carlo calculations

“…[18][19][20][21][22] The earliest systematic study of Cu-containing NiMnGa showed that addition of Cu on Ni site rapidly suppresses martensitic transformation in Ni 2Àx Cu x MnGa which disappears for the x ¼ 0.1 composition. 23 When nominal content of Ni is kept stoichiometric in Ni 2 MnGa, the addition of Cu to this ternary Heusler compound allows one to smoothly adjust both magnetic and structural transition temperatures [24][25][26] or brings about an uncommon transformation sequence from low-temperature non-magnetic martensite to high-temperature ferromagnetic austenite.…”