Imaging Current-Induced Switching of Antiferromagnetic Domains in CuMnAs

Abstract

The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using X-ray Magnetic Linear Dichroism microscopy, we show that staggered effective fields generated by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multi-domain antiferromagnetic films.Antiferromagnetic (AF) materials are of increasing interest both for fundamental physics and applications. Recent advances in detecting and manipulating AF order electrically have opened up new prospects for these materials in basic and applied spintronics research [1][2][3][4][5][6][7]. Of particular interest is the Néel order spin-orbit torque (NSOT) [6], recently demonstrated in the collinear AF CuMnAs [7], where a current-induced local spin polarization can exert a rotation of the magnetic sublattices. NSOT is closely analogous to the spin-orbit torque in ferromagnets with broken inversion symmetry, in which electrical currents induce effective magnetic fields that can be used to switch the magnetization direction [8,9]. The tetragonal CuMnAs lattice [10] is inversion symmetric, so that zero net spin polarization is generated by a uniform electric current. However, its Mn spin sublattices form inversion partners, resulting in local effective fields of opposite sign on the AF-coupled Mn sites [6,11]. These staggered current-induced fields can be large enough to cause a non-volatile rotation of the AF spin axis [7].Current-induced rotations of AF moments can be detected electrically using anisotropic magnetoresistance (AMR), a dependence on the relative orientation of the current and spin axes which is present in both ferromagnetic and AF materials [12][13][14][15]. This provides only spatially averaged information over the probed area of the device, which may be several microns or larger. PhotoEmission Electron Microscopy (PEEM), with contrast enabled by X-ray Magnetic Linear Dichroism (XMLD), provides direct imaging of AF domains with better than 100 nm resolution [16]. Based on differences in absorption of x-rays with linear polarization, XMLD-PEEM has offered valuable insights into the microscopic magnetic properties of AF films [17] and ferromagnet / AF interfaces [18,19]. The measured intensity varies as I 0 + I 2 cos 2 α, where α is the angle between the x-ray polarization and the spin axis [20], so is equally present for AF and FM materials, similar to AMR. The XMLD amplitude given by I 2 also depends on the orientation of the x-ray polarization with respect to the crystalline axes [21,22], and the signal is sensitive to domains within the top few nanometers of the surface.Here, we combin...

Antiferromagnetic CuMnAs multi-level memory cell with microelectronic compatibility

“…2a) and by measuring the AF transverse anisotropic magnetoresistance (planar Hall effect) across the other arm816. We note that ohmic anisotropic magnetoresistance (AMR) of comparable magnitude to our CuMnAs films13 was also utilized in the first generation of MRAM integrated circuits using thin-film uniaxial ferromagnets and bridge formation in the read circuitry, comprising reference and storing cells, for eliminating thermal and noise effects111718.…”

“…A complementary study performed at the Diamond Light Source directly associated the electrical switching signal in a CuMnAs cross structure with 10 μm wide arms with the AF moment reorientations within multiple domains of sub-micron dimensions13. In the experiment, several pairs of orthogonal, 50 ms writing pulses were applied and the corresponding domain reconfigurations were detected by means of the photoemission electron microscopy (PEEM) with contrast enabled by x-ray magnetic linear dichroism (XMLD).…”

“…The multiple-stability, reflecting series of reproducible, electrically controlled domain reconfigurations13, is not favourable for maximizing the retention and the bit-cell size scalability. However, in combination with the simplicity of the bit-cell geometry and unique features of AFs stemming from their zero net moment, the multi-level nature may provide additional functionalities, such as a pulse counter, with a utility in future specialized embedded memory-logic components in the ‘More than Moore'14 internet of things (IoT) applications.…”

Magnetic domain configuration of (111)-oriented LaFeO3 epitaxial thin films

“…Recently, Wadley et al 5 demonstrated switching of the AF spin axis by electric current. Further it was shown that the magnetic domain orientation was correlated to the electrical resistance 6 and used in a multilevel memory device. 7 Both exchange-bias and AF dynamics depend on the AF domain structure, hence a detailed understanding of domain formation and possibly domain engineering are both essential for further device development.…”

Antiferromagnetic spintronics

“…36(a) and 38]: in CuMnAs via global electrical measurements (anisotropic magnetoresistance) Olejnik et al, 2017a) as well as via local direct imaging of the antiferromagnetic domains (x-ray magnetic linear dichroism photoelectron emission microscopy) (Grzybowski et al, 2017), and in Mn 2 Au via global electrical measurements (anisotropic magnetoresistance) (Bodnar et al, 2017;Meinert, Graulich, and Matalla-Wagner, 2017). CuMnAs and Mn 2 Au crystals possess local inversion symmetry breaking in bulk crystal, as explained (see also Table III), and display anisotropic magnetoresistance allowing for the electrical detection of the order parameter orientation.…”