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Understanding of Exchange Bias in Ferromagnetic/Antiferromagnetic Bilayers
Published in S. K. Sharma, Exchange Bias, 2017
M. Pankratova, A. Kovalev, M. Žukovič
One can also obtain the inhomogeneous magnetization in the FM film in the case of the geometrical frustration on the EB phenomenon and the hysteresis loops features. The geometrical frustration appears if the minimum of the system energy does not correspond to the minimum of all local interactions. An example of a geometrically frustrated system is a triangular lattice with the AFM interaction between each pair of magnetic moments. In this case, the frustration is observed because of the incompatibility between the local interactions and the lattice geometry. We study in Reference 29 that layered system FM/AFM consists of two monolayers on a triangular lattice with periodic boundary conditions. The cases of frozen (fixed) and nonfrozen AFM are studied.
Energy-harvesting materials based on the anomalous Nernst effect
Published in Science and Technology of Advanced Materials, 2019
Masaki Mizuguchi, Satoru Nakatsuji
Mn3Sn has a hexagonal crystal structure with space group of P63/mmc [49] (Figure 10(a)). Mn atoms form a kagome lattice in the ab-plane, and each Mn triangle on the kagome lattice is stacked on top along the c-axis. On cooling below the Néel temperature of 430 K, Mn magnetic moments of ~ 3µB lying in the ab-plane form a coplanar, 120-degree spin structure characterized by Q = 0 wave vector [50,51]. This structure is characterized by the negative sign of the vector chirality and called the inverse triangular spin structure, and stabilized by the combination of the geometrical frustration and Dzyaloshinskii–Moriya interactions (Figure 10(a)) [50–52]. Interestingly, this magnetic structure can be viewed as a ferroic (Q = 0) order of a cluster magnetic octupole shown in the inset of Figure 10(b), and thus breaks the time-reversal symmetry [53]. This symmetry breaking enables the observation of the Kerr effect in the antiferromagnetic metal [23]. In addition, it further induces a very tiny magnetization ~ 2 m µB/Mn, allowing us to switch the non-collinear antiferromagnetic structure by using magnetic field.
Strain effect on physical properties of the multiferroic Mn3Sn material: a first-principles calculations
Published in Philosophical Magazine, 2022
W. Bazine, N. Tahiri, O. El Bounagui, H. Ez-Zahraouy
Multiferroic materials have attracted remarkable interest due to their application on electronic devices such as actuators, magnetic sensors, tunnelling devices, magnetic/ferroelectric data storage media, spin-based devices (spintronics), magnetocapacitive devices, nonvolatile memories, random access memory, and novel memory devices [1–5]. Lately, research on intermetallic compounds has gained significant interest due to their remarkable applications in different areas such as optoelectronics, magnetism, spintronic, and thermoelectric. The Mn3Z (Z = Ga, Ge, and Sn) based compounds have attracted a lot of attention due to a variety of useful functions that have never been seen in antiferromagnetic at zero magnetic field, which include magneto-optical Kerr (MOKE) effect and piezoelectric at room temperature [6–12]. Moreover, they are controllable by a magnetic field and thus can be used for designing antiferromagnetic spintronic and energy harvesting technology [7,8]. Also, the topological antiferromagnetic Mn3Z (Z = Ge, Sn), the most striking of which, exhibits large anomalous Hall effect, anomalous Nernst effect, large magneto-optical Kerr effect, terahertz anomalous Hall effect, planar Hall effect, topological Hall effect, and other rich excellent properties [10]. These exotic properties originated from its unique non-collinear antiferromagnetic (AFM) structure. The multiferroic Mn3Sn material is a hexagonal antiferromagnetic phase, with has the multilayer MnSn-MnSn. For ( is the Néel temperature), the melding of inter-site antiferromagnetic (AF) and Dzyaloshinskii–Moriya (DM) interactions conducts to an inverse triangular spin structure, specifically, a 120° spin structure with a uniform negative vector chirality of the in-plane Mn moments owing of geometrical frustration [13–15]. This non-collinear AFM structure is obtained from the competition of three interactions counting Heisenberg exchange interaction, Dzyaloshinskii–Moriya (DM) interaction, and magnetocrystalline anisotropy [16]. Since Higo et al. [17] discovered a large magneto-optical Kerr effect (MOKE) in an antiferromagnetic metal Mn3Sn, they find that the non-collinear AF metal Mn3Sn [18], exhibits a large zero-field Kerr rotation angle of 20 deg at room temperature, comparable to ferromagnetic metals. Nyári et al. [19], studied the weak ferromagnetism in the Mn3Z (Z = Sn, Ge, and Ga) alloys using a combination of ab-initio and spin model calculations. Numerically confirmed the results of Chen et al. [20], and investigated in addition the noncollinear antiferromagnetic hexagonal compound Mn3Ge and Mn3Sn considering various coplanar and non-coplanar triangular magnetic configurations. Additionally in this case diverse spin-compensated configurations were identified that were expected to reveal an AHE. It was discovered recently that the noncollinear AFM Mn3XN (X = Ga, Zn, Ag, and Ni) exhibits a large AHE and MOKE via first-principles density functional calculations together with group-theory analysis and tight-binding modelling [21]. Recently, these predictions were be verified experimentally in Mn3Sn [18] and Mn3Ge [22,23].