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1. In-plane uniaxial pressure-induced out-of-plane antiferromagnetic moment and critical fluctuations in BaFe2As2

   https://doi.org/10.1038/s41467-020-19421-5  

   Liu, Panpan; Klemm, Mason L.; Tian, Long; Lu, Xingye; Song, Yu; Tam, David W.; Schmalzl, Karin; Park, J. T.; Li, Yu; Tan, Guotai; et al (December 2020, Nature Communications)

   null (Ed.)

   Abstract A small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFe 2 As 2 , which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature T s . Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature T N ( <  T s ) and create in-plane resistivity anisotropy above T s . Here we use neutron polarization analysis to show that such a strain on BaFe 2 As 2 also induces a static or quasi-static out-of-plane ( c -axis) AF order and its associated critical spin fluctuations near T N / T s . Therefore, uniaxial pressure necessary to detwin single crystals of BaFe 2 As 2 actually rotates the easy axis of the collinear AF order near T N / T s , and such effects due to spin-orbit coupling must be taken into account to unveil the intrinsic electronic/magnetic properties of the system. 

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2. Imaging the Néel vector switching in the monolayer antiferromagnet MnPSe3 with strain-controlled Ising order

   https://doi.org/10.1038/s41565-021-00885-5  

   Ni, Zhuoliang; Haglund, A. V.; Wang, H.; Xu, B.; Bernhard, C.; Mandrus, D. G.; Qian, X.; Mele, E. J.; Kane, C. L.; Wu, Liang (April 2021, Nature Nanotechnology)

   null (Ed.)

   Antiferromagnets are interesting materials for spintronics because of their faster dynamics and robustness against perturbations from magnetic fields. Control of the antiferromagnetic order constitutes an important step towards applications, but has been limited to bulk materials so far. Here, using spatially resolved second-harmonic generation, we show direct evidence of long-range antiferromagnetic order and Ising-type Néel vector switching in monolayer MnPSe3 with large XY anisotropy. In additional to thermally induced switching, uniaxial strain can rotate the Néel vector, aligning it to a general in-plane direction irrespective of the crystal axes. A change of the universality class of the phase transition in the XY model under uniaxial strain causes this emergence of strain-controlled Ising order in the XY magnet MnPSe3. Our discovery is a further ingredient for compact antiferromagnetic spintronic devices in the two-dimensional limit. 

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3. On the Transversely Isotropic, Hyperelastic Response of Central Nervous System White Matter Using a Hybrid Approach

   https://doi.org/10.1115/1.4049168  

   Pan, Yi; Shreiber, David I.; Pelegri, Assimina A. (February 2021, Journal of Engineering and Science in Medical Diagnostics and Therapy)

   Abstract A numerical and experimental hybrid approach is developed to study the constitutive behavior of the central nervous system white matter. A published transversely isotropic hyperelastic strain energy function is reviewed and used to determine stress–strain relationships for three idealized, simple loading scenarios. The proposed constitutive model is simplified to a three-parameter hyperelastic model by assuming the white matter's incompressibility. Due to a lack of experimental data in all three loading scenarios, a finite element model that accounts for microstructural axons and their kinematics is developed to simulate behaviors in simple shear loading scenarios to supplement existing uniaxial tensile test data. The parameters of the transversely isotropic hyperelastic material model are determined regressively using the hybrid data. The results highlight that a hybrid numerical virtual test coupled with experimental data, can determine the transversely isotropic hyperelastic model. It is noted that the model is not limited to small strains and can be applied to large deformations. 

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4. Study of material removal behavior on R-plane of sapphire during ultra-precision machining based on modified slip-fracture model

   https://doi.org/10.1016/j.npe.2020.07.001  

   Kwon, Suk_Bum; Nagaraj, Aditya; Yoon, Hae-Sung; Min, Sangkee (July 2020, Nanotechnology and Precision Engineering)

   In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed. 

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5. Direct Observation of Magnetic Transitions in a Nickel(II) Complex with Large Anisotropy

   https://doi.org/10.11862/CJIC.2020.126  

   Chelsea N. Widener, Alexandria N. (June 2020, Wuji huaxue xuebao)

   Trigonal bipyramidal Ni(II) complex [Ni(Me6tren)Cl](ClO4) (1, Me6tren = tris[2-(dimethylamino)ethyl]amine) has recently been shown by Ruamps and coworkers to possess large, uniaxial magnetic anisotropy (J. Am. Chem. Soc. 2013, 135, 3017). Their HF-EPR studies gave rhombic zero-field-splitting (ZFS) parameter E = 1.56(5) cm-1 for 1. However, the axial ZFS parameter D has not been determined. We have used far-IR magnetic spectroscopy (FIRMS) at 0-17.5 T and 5 K to probe the magnetic transitions between the MS = 1 and MS = 0 states of the ground spin state S = 1 in 1. Direct observation of the transitions between Zeeman-split states in FIRMS give axial ZFS parameter D = -110.7(3) cm-1. Hirshfeld surface analysis of the crystal structure of 1 has been performed, revealing the interactions between the cation and anion in a molecule of 1 as well as among the molecules of 1 in crystals. 

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