Readout of an antiferromagnetic spintronics system by strong exchange coupling of Mn2Au and Permalloy

In antiferromagnetic spintronics, the read-out of the staggered magnetization or Néel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Néel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-established read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are only slightly diminished. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Néel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.

Ionitronic manipulation of current-induced domain wall motion in synthetic antiferromagnets

The current induced motion of domain walls forms the basis of several advanced spintronic technologies. The most efficient domain wall motion is found in synthetic antiferromagnetic (SAF) structures that are composed of an upper and a lower ferromagnetic layer coupled antiferromagnetically via a thin ruthenium layer. The antiferromagnetic coupling gives rise to a giant exchange torque with which current moves domain walls at maximum velocities when the magnetic moments of the two layers are matched. Here we show that the velocity of domain walls in SAF nanowires can be reversibly tuned by several hundred m/s in a non-volatile manner by ionic liquid gating. Ionic liquid gating results in reversible changes in oxidation of the upper magnetic layer in the SAF over a wide gate-voltage window. This changes the delicate balance in the magnetic properties of the SAF and, thereby, results in large changes in the exchange coupling torque and the current-induced domain wall velocity. Furthermore, we demonstrate an example of an ionitronic-based spintronic switch as a component of a potential logic technology towards energy-efficient, all electrical, memory-in-logic.

Recent Developments on MnN for Spintronic Applications

There is significant interest worldwide to identify new antiferromagnetic materials suitable for device applications. Key requirements for such materials are: relatively high magnetocrystalline anisotropy constant, low cost, high corrosion resistance and the ability to induce a large exchange bias, i.e., loop shift, when grown adjacent to a ferromagnetic layer. In this article, a review of recent developments on the novel antiferromagnetic material MnN is presented. This material shows potential as a replacement for the commonly used antiferromagnet of choice, i.e., IrMn. Although the results so far look promising, further work is required for the optimization of this material.

Frequency multiplication by collective nano-scale spin wave dynamics

Frequency multiplication is a process where harmonic multiples of the input frequency are generated. It is usually achieved in non-linear electronic circuits or transmission lines. Such elements enable the up-conversion of electronic signals to GHz frequencies and are essential for frequency synthesizers and communication devices. Circuits based on the propagation and interaction of spin waves are a promising alternative to conventional electronics. Unfortunately, these systems usually require direct driving in the GHz range as magnonic frequency up-conversion is restricted to a few harmonics only. Here we show that the ferromagnetic material itself can act as a six octave spanning frequency multiplier. By studying low frequency magnetic excitations in a continuous ferromagnetic layer we show that the non-linearity of magnetization dynamics combined with disorder in the ferromagnet leads to the emergence of a dynamic phase generating high harmonics. The demonstrated broad band frequency multiplication opens exciting perspectives for magnonic and spintronic applications since the frequency is up-converted from MHz into GHz frequencies within the magnetic medium itself. Due to the ease at which magnetic media can be structured and modified spatially (and reversibly) we anticipate that a tailored non-linear dynamic phase can be engineered e.g. to stabilize magnetic solitons.

X-ray Photoemission Spectroscopy Study of Uniaxial Magnetic Anisotropy Induced in a Ni Layer Deposited on a LiNbO3 Substrate

The competition between magnetic shape anisotropy and the induced uniaxial magnetic anisotropy in the heterojunction between a ferromagnetic layer and a ferroelectric substrate serves to control magnetic domain structures as well as magnetization reversal characteristics. The uniaxial magnetic anisotropy, originating from the symmetry breaking effect in the heterojunction, plays a significant role in modifying the characteristics of magnetization dynamics. Magnetoelastic phenomena are known to generate uniaxial magnetic anisotropy; however, the interfacial electronic states that may contribute to the uniaxial magnetic anisotropy have not yet been adequately investigated. Here, we report experimental evidence concerning the binding energy change in the ferromagnetic layer/ferroelectric substrate heterojunction using X-ray photoemission spectroscopy. The binding energy shifts, corresponding to the chemical shifts, reveal the binding states near the interface. Our results shed light on the origin of the uniaxial magnetic anisotropy induced from the heterojunction. This knowledge can provide a means for the simultaneous control of magnetism, mechanics, and electronics in a nano/microsystem consisting of ferromagnetic/ferroelectric materials.

Electrical Transport and Magnetic Properties of Metal/Metal Oxide/Metal Junctions Based on Anodized Metal Oxides

In this paper we present magnetoelectric properties of metal/metal-oxide/metal junctions. We use Ti and Fe as metallic layers separated by the porous metal-oxides of iron or titanium formed with the anodization method. This allowed to prepare double junctions with at least one ferromagnetic layer. Here we show magnetoresistance and current-voltage characteristics of the junctions together with their magnetic characteristics. We found positive or negative magnetoresistance depending on junction composition. We discuss also the nature of differential resistance calculated from I-V characteristics. Our findings show that the strongest influence on observed behaviour has a top metallic layer and the interface between this layer and anodized oxide where strong interatomic diffusion is expected.

VISUALIZING THE DISTRIBUTION OF SPIRAL MAGNETIZATION IN THE FERROMAGNETIC LAYER OF A SUPERCONDUCTING SPIN VALVE

In this paper, we investigate the switch of a magnet-based superconducting spin valve. As a magnet, we consider the MnSi compound characterized by a complex magnetic structure with its magnetization in the form of a spiral helicoid. A model is given for a double-layered superconducting spin valve based on the spiral magnet with an adjoining superconducting thin layer. As shown previously, critical temperature of such a superconducting film depends on the direction of the spiral magnet. Calculations have been performed for magnetic dynamics of this structure, which in prospect can serve as the basis for creating memory or logic elements of low temperature nanoelectronics. Several problems have been treated with regards to mathematical simulation of switching the spin valve magnetization, research on the spin valve structure using electromagnetic simulation software to change magnetization and rotation of the spiral magnetic vector under the magnetic-field pulse, construction and analysis of 3D magnetization distributions in spiral magnets to trace the process of remagnetization. In this work, we use a Matlab-based software environment and tools for constructing distribution plots of vector fields. It is shown that the direction of the spiral magnet can be switch by pulsed magnetic field. Research has been done on the resultant magnetization distributions visualized in the form of vector fields.