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A feedback modification method based on variable separation mapping is proposed in the design of free-form optical system with uniform illuminance for LED source. In this method, the non-negligible size of LED source is taken into account, and a smooth optical system is established with single freeform surface regenerated by adding feedback to the lens design for a point light source. More rounds of feedback can improve the lens performance. As an example, a smooth free-form lens with rectangular illuminance distribution is designed, and the illuminance uniformity is improved from 18.75% to 81.08% after eight times feedback.

Spintronic devices based on antiferromagnetic (AFM) materials hold the promise of fast switching speeds and robustness against magnetic fields 1-3 . Different device concepts have been predicted 4,5 and experimentally demonstrated, such as low-temperature AFM tunnel junctions that operate as spin-valves 6 , or roomtemperature AFM memory, for which either thermal heating in combination with magnetic fields 7 , or Néel spin-orbit torque 8 is used for the information writing process. On the other hand, piezoelectric materials were employed to control magnetism by electric fields in multiferroic heterostructures 9-12 , which suppresses Joule heating caused by switching currents and may enable low energy-consuming electronic devices. Here, we combine the two material classes to explore changes of the resistance of the high-Néel-temperature antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile resistance states at room temperature and zero electric field, which are stable in magnetic fields up to 60 T. Furthermore, the strain-induced resistance switching process is insensitive to magnetic fields. Integration in a tunnel junction can further amplify the electroresistance. The tunneling anisotropic magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a piezoelectric, strain-controlled AFM memory which is fully operational in strong magnetic fields and has potential for low-energy and high-density memory applications.

In recent years, the field of antiferromagnetic spintronics has been substantially advanced. Electric‐field control is a promising approach for achieving ultralow power spintronic devices via suppressing Joule heating. Here, cutting‐edge research, including electric‐field modulation of antiferromagnetic spintronic devices using strain, ionic liquids, dielectric materials, and electrochemical ionic migration, is comprehensively reviewed. Various emergent topics such as the Néel spin–orbit torque, chiral spintronics, topological antiferromagnetic spintronics, anisotropic magnetoresistance, memory devices, 2D magnetism, and magneto‐ionic modulation with respect to antiferromagnets are examined. In conclusion, the possibility of realizing high‐quality room‐temperature antiferromagnetic tunnel junctions, antiferromagnetic spin logic devices, and artificial antiferromagnetic neurons is highlighted. It is expected that this work provides an appropriate and forward‐looking perspective that will promote the rapid development of this field.

We propose an improved double freeform-optical-surface design method for shaping a prescribed irradiance distribution whilst forming a desired wavefront from a given incident beam. This method generalizes our previous work [Opt. Exp. 21, 14728-14735 (2013)] to tackle non-separable beam irradiances. We firstly compute a proper ray mapping using an adaptive mesh method in the framework of the L2 Monge-Kantorovich mass transfer problem. Then, we construct the two freeform optical surfaces according to this mapping using a modified simultaneous point-by-point procedure which is aimed to minimize the surface errors. For the first surface, the modified procedure works by firstly approximating a value to the next point by only using the slope of the current point and then improving it by utilizing both slopes of the two points based on Snell's law. Its corresponding point on the second surface can be computed using the constant optical path length condition. A design example of producing a challenging irradiance distribution and a non-ideal wavefront demonstrates the effectiveness of the method.

antiferromagnet involves the antiferromagnetic exchange field H E as well due to spin canting via ω AFM ≈ ≈ 2 E A SF r H H rH , where r is the gyromagnetic ratio of an electron. It can be three orders of magnitude higher than that of ferromagnets ω FM ≈ rH A (typically GHz) and reaches THz. For example, the study on the laser-induced spin reorientation in antiferromagnetic TmFeO 3 in 2004 shows that the antiferromagnetic spins can be manipulated on a timescale of a few picoseconds. [1] In 2006, Núñes et al. proposed a pioneering theory that spin transfer torques can induce the order parameter orientation switching in antiferromagnetic metals, which is well similar to the ferromagnetic case. [2] However, they pointed out that compared with the ferromagnetic case, the critical current for antiferromagnetic order parameter switching can be smaller because of the absence of shape anisotropy and also because spin torques can act through the entire volume of an antiferromagnet. On the other hand, as the magnetic order in an antiferromagnet is staggered, only correspondingly staggered torques can drive coherent order parameter switching. Soon in 2007, different experimental groups demonstrated that the exchange bias of a ferromagnet/antiferromagnet bilayer system can be altered by a current and thus provided indirect evidences for current-induced torques in antiferromagnetic metals. [3][4][5] Subsequently, Gomonaȋand Loktev proposed the phenomenological model that describes the spin transfer torques in antiferromagnets. [6,7] These early studies were summarized by MacDonald and Tsoi in the review paper that emphasizes the concept of antiferromagnetic metal spintronics [8] and also by Gomonay and Loktev in the review paper that emphasizes spintronics of antiferromagnetic systems from a theoretical point of view. [9] In 2011, Park et al. creatively reversed the stacking order of the antiferromagnetic layer IrMn and the ferromagnetic layer NiFe in a spin-valve-like tunnel junction structure, where the antiferromagnetic IrMn served as the key functional layer for generating tunnel anisotropic magnetoresistance, while the ferromagnetic NiFe layer was utilized to rotate the antiferromagnetic spin axis of IrMn via the interfacial exchange spring effect. [10] Surprisingly, a more than 100% tunneling anisotropic magnetoresistance was achieved at 4 K. This device proves that antiferromagnetic materials could work as pivotal components in spintronic devices instead of simply serving as pinning Antiferromagnets naturally exhibit three obvious advantages over ferromagnets for memory device applications: insensitivity to external magnetic fields, much faster spin dynamics (≈THz), and higher packing density due to the absence of any stray field. Recently, antiferromagnetic spintronics has emerged as a cutting-edge field in the magnetism community.The key mission of this rapidly rising field is to steer the spins or spin axes of antiferromagnets via external stimuli and then realize advanced devices based on their physical property cha...

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approach that is capable of suppressing Joule heating is highly desirable from an energy perspective.Under this background, electric-field control of magnetism emerges in the field of multiferroics, which is expected to reduce the energy consumption of information storage by several orders of magnitude, to fJ bit −1 or even aJ bit −1 . [4][5][6][7][8][9][10][11] In single-phase multiferroic materials, which consists of more than one ferroic order, if there is coupling among different ferroic orders, for example, the magnetoelectric coupling between the ferroelectric (FE) and FM orders, the magnetism can be conveniently controlled by electrical switching of the ferroelectricity, such as in YMnO 3 , BiFeO 3 , and TbMnO 3 . However, the magnetic order in these materials is typically antiferromagnetic, which is difficult to detect, and the magnetoelectric coupling is rather weak; [12][13][14] moreover, intrinsic single-phase multiferroic materials are rare because of contradicting symmetry and physical requirements. [15] All these factors prevent single-phase multiferroic materials from practical device applications.Alternatively, the electric-field control of magnetism can be achieved in heterostructures via other means: (1) in FM/FE composite heterostructures, the magnetism of the FM thin films can be modulated by the piezoelectric strain triggered by electric fields applied onto the ferroelectric substrates; [8] (2) in FM/dielectric composite heterostructures with ultrathin FM thin films, the magnetism can be tailored by the electrostatic doping; [8] (3) in FM/multiferroic composite heterostructures, the magnetism of the FM thin film layers can be varied by electric fields through the interfacial magnetic exchange coupling, such as in Co 0.9 Fe 0.1 /BiFeO 3 heterostructures. [16] Typically, the modulation of magnetism by electric fields in multiferroic heterostructures results in variations in the magnetization, coercivity fields, or magnetic anisotropy of the ferromagnetic materials. In addition, the key scientific issue of controlling magnetic properties using an electric field has been carefully elaborated in previous Reviews. [17,18] Among them, the change of magnetization (ΔM) upon external electric fields (ΔE) yields the simplified magnetoelectric coupling coefficient (strictly speaking, the magnetoelectric coupling coefficient should be described as a tensor; please refer to the previous Reviews) [17,18] α = μ 0 ΔM/ΔE, where μ 0 is the permittivity of free space. Compared with single-phase multiferroics, α in multiferroic heterostructures can be significantly greater, for example, it reaches 1.08 × 10 −7 s m −1 Using an electric field instead of an electric current (or a magnetic field) to tailor the electronic properties of magnetic materials is promising for realizing ultralow-energy-consuming memory devices because of the suppression of Joule heating, especially when the devices are scaled down to the nanoscale. Here, recent results on giant magnetization and resistivity modulation in a metamagnetic inte...