Magnetization property in Ta/NiFe/Ta sandwich structure

Long, Jianguo; Zhai, Ya; Chen, J; Du, Jun; Pan, Minghu; Lu, M.; Hu, An; Zhai, Hongru

doi:10.1016/s0304-8853(00)00865-9

Cited by 7 publications

(9 citation statements)

References 11 publications

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“…NRM, also known as negative coercivity or inverted hysteresis loop, has been observed in heterogeneous thin films, and heterogeneous NP systems (with amorphous matrix, large particle size distribution or core shell structure) by various experimental techniques (e.g., Vibrating Sample Magnetometer, SQUID magnetometry, Alternating Gradient Force, Magneto-optical Kerr Effect and Hall probe imaging)123456789. In normal magnetic behavior the magnetization follows the applied field with a phase lag, whereas in magnetic systems that display NRM, the magnetization of the descending branch of the hysteresis loop becomes negative while the applied field is still positive.…”

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confidence: 99%

Physical Justification for Negative Remanent Magnetization in Homogeneous Nanoparticles

Zhang

et al. 2014

Sci Rep

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The phenomenon of negative remanent magnetization (NRM) has been observed experimentally in a number of heterogeneous magnetic systems and has been considered anomalous. The existence of NRM in homogenous magnetic materials is still in debate, mainly due to the lack of compelling support from experimental data and a convincing theoretical explanation for its thermodynamic validation. Here we resolve the long-existing controversy by presenting experimental evidence and physical justification that NRM is real in a prototype homogeneous ferromagnetic nanoparticle, an europium sulfide nanoparticle. We provide novel insights into major and minor hysteresis behavior that illuminate the true nature of the observed inverted hysteresis and validate its thermodynamic permissibility and, for the first time, present counterintuitive magnetic aftereffect behavior that is consistent with the mechanism of magnetization reversal, possessing unique capability to identify NRM. The origin and conditions of NRM are explained quantitatively via a wasp-waist model, in combination of energy calculations.

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confidence: 99%

Physical Justification for Negative Remanent Magnetization in Homogeneous Nanoparticles

Zhang

et al. 2014

Sci Rep

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“…2(b) of Ref. 5. Figure 4(a) shows the case of triplet loops, which was often observed in experiments.…”

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confidence: 60%

“…The latter could be either double loops or triplet loops, which also includes the case of inverted loops. [2][3][4][5][6][7] Phenomenological models have been used to explain the anomalous loops by exchange-coupled bilayers 2,3,6,8,9 or by introducing higher-order anisotropy. 4,10 In exchange-coupled bilayer models, the system consisted of two FM layers.…”

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confidence: 99%

“…Figure 4(a) shows the case of triplet loops, which was often observed in experiments. [2][3][4][5][6] Figure 4(b) plots corresponding ͗S ␣ z ͘ of all ML's with increasing field. Here because of strong interfacial exchange, ͉J 12 ͉ being at least a double of either J 1 or J 2 , the spins in the interfacial ML's, the fifth and sixth ML's, always point to directions opposite to each other if the field is not large enough.…”

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Individual monolayer analysis of anomalous hysteresis loops

2004

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Based on a quantum spin model and by using the many-body Green's function method, we discuss the mechanism of anomalous hysteretic loops for exchange-coupled ultrathin bilayers by analyzing in detail the spin behavior in all monolayers. Spins in each monolayer can flip abruptly to generate steplike or triplet loops, or they can reverse gradually to generate double loops. Specially, the spins in an interfacial monolayer may be oriented in the opposite direction from those in the other monolayers of a given layer under a strong interfacial antiferromagnetic exchange. This individual monolayer analysis improves the earlier understanding of the anomalous hysteresis loops by phenomenological models.Anomalous hysteresis loops could occur experimentally in ferromagnetic (FM) films. Here we mean the anomalous loops as steplike 1,2 and multiloops. The latter could be either double loops or triplet loops, which also includes the case of inverted loops. 2-7 Phenomenological models have been used to explain the anomalous loops by exchange-coupled bilayers 2,3,6,8,9 or by introducing higher-order anisotropy. 4,10 In exchange-coupled bilayer models, the system consisted of two FM layers. Each FM layer was assigned a magnetization, the magnitude of which was independent of external field, but could rotate under an external field. There was an antiferromagnetic (AFM) exchange between the two magnetizations. The orientations of the magnetizations were not always along the field direction. Hence the magnetizations of both layers had projections on the field direction. The combination of the projections made up the anomalous loops.If one realizes the system from a microscopic view, the physical picture will be different from what the phenomenological model gave. In a microscopic model, each FM layer consists of several monolayers (ML's), and each ML is in turn composed of spins at crystalline sites. Every spin interacts with its neighbors by Heisenberg exchange interaction. As there is a lack of translation invariance along the out-ofplane direction, the behavior of the spins may be different from ML to ML. The interaction between the two FM layers is in fact an AFM interfacial exchange, not just the interaction between the two magnetizations. Thus the behavior of the spins inside each FM layer may not be uniform, and neither can the behavior of each layer be recognized as a single magnetization. Compared with the microscopic model, a phenomenological model seemed too rough. A detailed microscopic explanation based on quantum mechanics should help us to understand the physics of the anomalous loops more clearly. In this paper, we present a monolayer spin-flip or spin-reversal picture of the anomalous loops for ultrathin exchange-coupled bilayer.The Hamiltonian we use includes three parts:H 1 is the Hamiltonian of the first FM layer:The first term is the Heisenberg FM exchange in each ML, where only the nearest-neighbor interaction is considered.Here i and j label sites and the Greek letters label ML's. The second term is the Heisen...

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“…The Mn 0.4 Ge 0.6 :H film exhibits ferromagnetism and the saturation magnetization decreases with increasing temperature. However, the coercivity of Mn 0.4 Ge 0.6 :H film is 1800 Oe at 5 K, -14 Oe at 50 K, and 30 Oe at 150 K. Although the negative coercivity due to the antiferromagnetic coupling has been observed in an exchange-coupled multilayer system, [22][23][24] granular films, [25][26][27][28] and a magnetic semiconductor, [29] the oscillation of coercivity with temperature has not been discovered in FMS and hydrogenated systems yet.…”

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confidence: 99%

Oscillation of coercivity between positive and negative in Mn_xGe_1−x:H ferromagnetic semiconductor films

Qin¹,

Shen²,

Xiao³

et al. 2013

Chinese Phys. B

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Amorphous MnxGe1−x:H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1−x:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1−x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6:H film, the inverted Hall loop is also observed at 30 K, which is consistent with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1−x films for the application in spintronics.

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Magnetization property in Ta/NiFe/Ta sandwich structure

Cited by 7 publications

References 11 publications

Physical Justification for Negative Remanent Magnetization in Homogeneous Nanoparticles

Physical Justification for Negative Remanent Magnetization in Homogeneous Nanoparticles

Individual monolayer analysis of anomalous hysteresis loops

Oscillation of coercivity between positive and negative in Mn_xGe_1−x:H ferromagnetic semiconductor films

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Magnetization property in Ta/NiFe/Ta sandwich structure

Cited by 7 publications

References 11 publications

Physical Justification for Negative Remanent Magnetization in Homogeneous Nanoparticles

Physical Justification for Negative Remanent Magnetization in Homogeneous Nanoparticles

Individual monolayer analysis of anomalous hysteresis loops

Oscillation of coercivity between positive and negative in MnxGe1−x:H ferromagnetic semiconductor films

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Oscillation of coercivity between positive and negative in Mn_xGe_1−x:H ferromagnetic semiconductor films