Spin dynamics in a Curie-switch

Kravets, A. F.; Tovstolytkin, A. I.; Dzhezherya, Yu. I.; Polishchuk, Dmytro; Kozak, I. M.; Korenivski, Vladislav

doi:10.1088/0953-8984/27/44/446003

Cited by 16 publications

(35 citation statements)

References 22 publications

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“…In conclusion, we show that, at temperatures close to T c of the Ni 67 Cu 33 spacer, Ni 80 Fe 20 /Ni 67 Cu 33 /Co 90 Cu 10 /Mn 80 Ir 20 multilayers exhibit the isothermal magnetic entropy changes S M´s , which are much larger than this quantity in a single Ni 67 Cu 33 paramagnet subjected to a moderate magnetic field H. The enhanced magnetocaloric efficiency in our samples results from the magnetic-field-driven reconfiguration of the soft ferromagnet (NiFe) with respect to the pinned one (CoFe). 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.…”

Section: Resultssupporting

confidence: 87%

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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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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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Section: Resultssupporting

confidence: 87%

“…It is also important that the T c of the spacer can be tunable by varying the spacer composition. For example, a diluted Ni x Cu 1-x alloy, whose T c depends almost linearly on the Ni concentration, is a good candidate as the spacer material [14][15][16][17]. Fig.1.…”

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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 soft Permalloy layer (Py = Ni 80 Fe 20 ) provides low coercivity of F free , whereas the ultra-thin Fe(0.5) is used to increase the electron spinpolarization at the F free /N interface, which greatly enhances the strength of the RKKY interaction [28]. The gradient spacer N/f/N, with N = Cr(1) and f = Fe 25 Cr 75 , has the thickness of the pure Cr layers (1 nm) chosen to correspond to strong antiferromagnetic RKKY (first antiferromagnetic RKKY peak). The nominally weakly ferromagnetic Fe 25 Cr 75 inner spacer is well lattice matched within the Cr/Cr-Fe/Cr spacer, has near perfect miscibil-ity of Fe in Cr, and has a suitably low bulk Curie temperature of T C ≈ 150 K [29,30].…”

Section: B Thermomagnetic Rkky-vs-intrinsic Exchange Tuning: Multilamentioning

confidence: 99%

“…The gradient spacer N/f/N, with N = Cr(1) and f = Fe 25 Cr 75 , has the thickness of the pure Cr layers (1 nm) chosen to correspond to strong antiferromagnetic RKKY (first antiferromagnetic RKKY peak). The nominally weakly ferromagnetic Fe 25 Cr 75 inner spacer is well lattice matched within the Cr/Cr-Fe/Cr spacer, has near perfect miscibil-ity of Fe in Cr, and has a suitably low bulk Curie temperature of T C ≈ 150 K [29,30]. The intriguing thickness range for the inner spacer f is a few monolayers (t f ∼ 1 nm), where, as detailed in the sections that follow, the combined interfacial RKKY exchange from the two outer Fe electrodes becomes comparable in magnitude to the intrinsic exchange within the Cr-Fe alloy and can add to it (parallel F free and F pin ) or mutually subtract (antiparallel F free and F pin ), thereby driving a magnetic phase transition in the structure, with a tunable operating (Curie) point.…”

Section: B Thermomagnetic Rkky-vs-intrinsic Exchange Tuning: Multilamentioning

confidence: 99%

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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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Ferromagnetic resonance in nanostructures with temperature-controlled interlayer interaction

Polishchuk

Tykhonenko-Polishchuk

Kravets

et al. 2016

Low Temperature Physics

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This study is a comprehensive analysis of a multilayer F1/f(d)/F2pin structure's magnetic resonance properties, wherein F1 and F2pin are the free and exchange-coupled strong magnetic layers, and f is the weakly magnetic layer with a Curie point in the room temperature region. Depending on the magnetic state of the spacer f (ferromagnetic or paramagnetic) the exchange interaction between the F2 and F2pin layers becomes a function of the temperature, which opens up opportunities for practical applications. The obtained results show that the interlayer exchange coupling can be enhanced by decreasing the thickness of the spacer d, or by lowering the temperature. Strengthening the exchange coupling leads to a stronger manifestation of unidirectional anisotropy in the ferromagnetic resonance layer F1, as well as to a broadening of the resonance line that is atypical for thin films. The observed features are analyzed in the context of comparing the effects of two different natures: the influence of the spacer d and the influence of the temperature. Thus, the behavior of changes to the unidirectional anisotropy remains the same given variation of both the thickness of the spacer and the temperature. However the broadening of the magnetic resonance line is more sensitive to changes in the interlayer interaction caused by variation of d, and is less susceptible to changes caused by temperature.

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Spin dynamics in a Curie-switch

Cited by 16 publications

References 22 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

Ferromagnetic resonance in nanostructures with temperature-controlled interlayer interaction

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