Magnetocaloric effect in ferromagnet/paramagnet multilayer structures

Abstract

The magnetocaloric effect in ferromagnet/paramagnet multilayer structures is studied in the framework of the Landau phenomenological theory of phase transitions. The performed estimations demonstrate the possibil ity of achieving record cooling efficiency with such structures.

High magnetocaloric efficiency of a NiFe/NiCu/CoFe/MnIr multilayer in a small magnetic field

“…Switching of magnetic moments in the NiFe alters the magnetization distribution in the Ni 67 Cu 33 spacer [14][15][16][17], which should provide the enhanced MCE in accordance to our calculations performed in Ref. [11]: The thinner spacer, the stronger its magnetization/demagnetization by the ferromagnetic surroundings, and the higher MCE.…”

“…Switching of magnetic moments in the NiFe alters the magnetization distribution in the Ni 67 Cu 33 spacer [14][15][16][17], which should provide the enhanced MCE in accordance to our calculations performed in Ref. [11]: The thinner spacer, the stronger its magnetization/demagnetization by the ferromagnetic surroundings, and the higher MCE. Indeed, having compared the quantities of  0 M/T in the samples with thin (10 nm) and thick (21 nm) spacers, we mark that the peak values of  0 M/T are higher in the sample with a thinner spacer (Fig.…”

“…Therefore, there is a task to seek for MCE materials, in their both bulk and thin-film forms [8][9][10], that could be used for magnetic cooling with moderate fields. We propose to enhance the MCE by surrounding a magnetocaloric material by higher-T c FM's, [11,12] so that their reconfigurations in moderate H could provide magnetizing/demagnetizing the PM spacer due to the effect of proximity [13]. It has been shown [12, 14-17] that FM layers surrounding the PM (or weakly FM) spacer strongly affect its magnetization up to the spacer thickness of  20 nm [12].Here we report on our measurements of S M in Ni 80 Fe 20 /Ni 67 Cu 33 /Co 90 Cu 10 /Mn 80 Ir 20 stacks at T close to T c of the Ni 67 Cu 33 spacer between the FM layers, i.e., Ni 80 Fe 20 and Co 90 Fe 10 .…”

“…If magnetizations in the FM layers, F 1 and F 2 , are oriented in the same direction (left), the spacer is magnetized (low magnetic entropy) by the exchange interactions with the F 1 and F 2 layers across the interfaces, while the spacer is demagnetized (high magnetic entropy) in the opposite case by reconfiguring magnetizations in the FM layers (right) with an external magnetic field H. In this thought experiment, the temperature is close to T c. of the spacer. Therefore, the reconfiguration of magnetizations in the FM layers is expected to provide a strong MCE [11,12] by analogy with the effect of giant magnetoresistance [18,19].…”

Giant magnetocaloric effect driven by indirect exchange in magnetic multilayers

“…In particular, in a trilayer F 1 /f/F 2 [22,23], where a low-T C spacer (f) mediates exchange between two high-T C ferromagnets (F 1 and F 2 ), the outer ferromagnets exert a strong magnetic proximity effect on f due to the direct exchange coupling at the interfaces. In the vicinity of the spacers T C , the parallel-antiparallel switching of the magnetic moments of F 1 and F 2 has recently been predicted to yield a strong entropy change in the system (∆S ∼ −1 mJ cm −3 K −1 ) [24]. This difference in magnetic entropy between the parallel (P) and antiparallel (AP) orientations was estimated via the proximity effect on the spacer from the strongly ferromagnetic outer layers, with the contributions from the two interfaces expected to add up or cancel out in the P or AP states of the trilayer, respectively.…”