Isothermal entropy changes in nanocomposite Co:Ni67Cu33

Michalski, Steven A.; Skomski, Ralph; Li, X. Zh; Roy, Damien; Mukherjee, Tathagata; Binek, Ch.; Sellmyer, David J.

doi:10.1063/1.3676423

Cited by 9 publications

(7 citation statements)

References 24 publications

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“…In Fig. 2 (b) we show H sw versus T near T c 240 K of the Ni 67 Cu 33 [20] for two samples  with thicknesses of the Ni 67 Cu 33 spacer of 10 nm and 21 nm. The fact that H sw depends on T indicates that the interaction through the spacer is sensitive to the temperature.…”

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confidence: 99%

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

et al. 2018

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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

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

et al. 2018

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“…by the intrinsic RKKY in the nanostructure. This is in contrast to the conventional approach of using nanostructuring for tailoring the nano-material's magnetic properties, such as the direct exchange and anisotropy, aimed at enhancing the MCE in low magnetic fields, adjusting its operating temperature, or suppressing unwanted hysteresis losses [17][18][19][20]. The conventional approach often yields only minor improvements in the magnetocaloric properties, in particular due to the relatively low energy of magnetic anisotropy compared to that of thermal fluctuations near room temperature.…”

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confidence: 97%

Giant magnetocaloric effect driven by indirect exchange in magnetic multilayers

Polishchuk

Tykhonenko-Polishchuk

Holmgren

et al. 2018

Phys. Rev. Materials

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Indirect exchange coupling in magnetic multilayers, also known as the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, is highly effective in controlling the interlayer alignment of the magnetization. This coupling is typically fixed at the stage of the multilayer fabrication and does not allow ex-situ control needed for device applications. In addition to the orientational control, it is highly desirable to also control the magnitude of the intralayer magnetization, ideally switch it on/off by switching the relevant RKKY coupling. Here we demonstrate a magnetic multilayer material, incorporating thermally-as well as field-controlled RKKY exchange, focused on to a dilute ferromagnetic alloy layer and driving it though its Curie transition. Such on/off magnetization switching of a thin ferromagnet, performed repeatably and fully reproducibly within a low-field sweep, results in a giant magnetocaloric effect, with the estimated isothermal entropy change of ∆S ≈ −10 mJ cm −3 K −1 under an external field of ∼10 mT, which greatly exceeds the performance of the best rare-earth based materials used in the adiabatic-demagnetization refrigeration systems.

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“…A large MCE was predicted for a system of macrospins (∼100 µ B ) embedded into a weakly magnetic matrix, amplified by the interparticle exchange [19,21]. Subsequent experiments on magnetic nano-composites [22,23] and RKKY-coupled superlattices [20] have indeed shown large isothermal entropy changes of up to ∆S max = -0.4 J/kg K in a field of 7 T. A conceptually different multilayer system, based on thermally controlled RKKY [30][31][32], showed a giant MCE of ∆S max = -1.4 J/kg K in fields as low as 10 mT [24]. The magneto-calorically active layer was a dilute ferromagnet undergoing an RKKY-induced magnetic phase transition on antiparallel-to-parallel magnetization switching in the system.…”

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confidence: 98%

“…Nanostructuring was recently shown to yield greatly enhanced MCE in materials containing no rare-earth elements [2,[19][20][21][22][23][24] via controlling the relevant anisotropy and exchange parameters [25]. The approach exploits the finite-size effects in nanostructures, where the interface and bulk contributions are energetically comparable.…”

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Inverse magnetocaloric effect in synthetic antiferromagnets

Polishchuk¹,

Persson²,

Kulyk³

et al. 2021

Preprint

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The magnetocaloric effect in exchange-coupled synthetic-antiferromagnet multilayers is investigated experimentally and theoretically. We observe a temperature-controlled inversion of the effect, where the entropy increases on switching the individual ferromagnetic layers from anti-parallel to parallel alignment near their Curie point. Using a microscopic analytical model as well as numerical atomistic-spin simulations of the system, we explain the observed effect as due to the interplay between the intra-and inter-layer exchange interactions, which either add up or counteract to effectively modulate the Curie temperature of the dilute ferromagnetic layers. The proposed method of designing tunable, strongly magneto-caloric materials should be of interest for such applications as heat-assisted spintronics and magnetic refrigeration.

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Isothermal entropy changes in nanocomposite Co:Ni67Cu33

Cited by 9 publications

References 24 publications

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

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

Giant magnetocaloric effect driven by indirect exchange in magnetic multilayers

Inverse magnetocaloric effect in synthetic antiferromagnets

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