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

Abstract

The isothermal magnetic entropy changes (S M 's) are studied in Ni 80 Fe 20 /Ni 67 Cu 33 /Co 90 Cu 10 /Mn 80 Ir 20 stacks at temperatures (T) near the Curie point (T c ) of the Ni 67 Cu 33 spacer by applying magnetic fields (H) in a few tens of Oersted. Such low values of H were sufficient for toggling magnetic moments in the soft ferromagnetic (FM) layer (Ni 80 Fe 20 ). It is found out that this switching provides the value of S M , which is up to 20 times larger than that achievable in a single Ni 67 Cu 33 film subjected to such low H. Our finding holds promise to be utilized in the magnetocaloric devices that would be based on FM/PM/FM heterostructures and would operate with moderate H.Introduction.  In materials that exhibit a strong magnetocaloric effect (MCE), the maximal magnetocaloric efficiency is basically achievable in the vicinity of phase magnetic transitions, e.g., near T c [1, 2]. The MCE, observed currently in record magnetocaloric materials, is believed to be sufficient for cooling down (or heating up) the material by applying H up to several tens of kilo-oersted over several tens of thermodynamic cycles [3][4][5][6]. However, such strong fields can only be produced with bulky magnets, which are undesired to be employed in magnetic refrigeration [7]. 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 . Such a heterostructure system exhibits reconfigurations of the mutual orientation of FM magnetizations, M 1 and M 2 , under applying a field of H sw 20 Oe due to their exchange decoupling across the spacer above its T c [14][15][16][17]. Our evaluations of the MCE in FM/PM/FM structures anticipate a very high MCE, dT/dH2.0 K/kOe in bias fields of only a few tens of oersted [11]. This MCE originates from magnetizing/demagnetizing the PM spacer when the mutual orientation of M 1 and M 2 , alters from parallel (antiparallel) to antiparallel (parallel). Such a reconfiguration in a F 1 /PM/F 2 /AF stack, where F 1 =Ni 80 Fe 20 , PM= Ni 67 Cu 33 , F 2 = Co 90 Fe 10 , and AF=Mn 80 Ir 20 is the antiferromagnetic layer, is schematically shown in Fig. 1. The role of the AF layer is to render the layer F 2 magnetically hard, which would contrasts to the magnetically soft layer F 1 . The dependence of S M on the mutual orientation of magnetizations of M 1 and

Proximity-Enhanced Magnetocaloric Effect in Ferromagnetic Trilayers

“…In a nanostructured trilayer consisting of one free and one pinned ferromagnetic layers, separated by a weakly ferromagnetic spacer, a field of the order of 100 Oe is sufficient to switch the outer ferromagnetic layers from parallel to antiparallel alignment and thereby reduce the effective exchange field in the spacer, which in turn leads to its demagnetization [9,10]. Such trilayer systems have been rather intensively studied recently, both in experiments and theoretically [11][12][13][14][15][16][17][18][19]. As regards MCE, first discussed by Fraerman and Shereshevskii [13], these studies have mostly been indirect experimentally (via magnetometry) and phenomenological in terms of modeling [13,[15][16][17][18][19], which introduces model-dependent uncertainties in the conclusions drawn.…”

“…Such trilayer systems have been rather intensively studied recently, both in experiments and theoretically [11][12][13][14][15][16][17][18][19]. As regards MCE, first discussed by Fraerman and Shereshevskii [13], these studies have mostly been indirect experimentally (via magnetometry) and phenomenological in terms of modeling [13,[15][16][17][18][19], which introduces model-dependent uncertainties in the conclusions drawn.…”

Magnetization induced second harmonic generation in thin films with ferromagnet/antiferromagnet interfaces

“…1, a): there are two loops of magnetic hysteresis characterizing the shifting of NiFe and CoFe layers, And both loops are offset against the zero value of the external field to H = 100−200 Oe for NiFe and H = 200−400 Oe for CoFe. Dependencies of this kind, typical of pinning composite structures, have been observed before [2,4,6] and are associated with the exchange effects of ferromagnetic layers with the antiferromagnet [16,18].…”

Генерация Магнитоиндуцированной Второй Гармоники В Тонких Пленках С Интерфейсами Ферромагнетик/Антиферромагнетик

“…В настоящей работе исследовалась мультислойная наноструктура состава NiFe(5)/NiCu(5)/CoFe(5)/ IrMn(10)/Ta(2) на стеклянной подложке (в скобках указаны толщины слоев в nm), а также двухслойные структуры CoFe(4)/IrMn (10) Зависимости такого вида, типичные для пиннингованных составных структур, наблюдались ранее [2,4,6] и связаны с эффектами обменного взаимодействия ферромагнитных слоев с антиферромагнитным [16,18].…”