Magnetic and structural properties of antiferromagnetic Mn2VSi alloy films grown at elevated temperatures

80 nm thick polycrystalline Mn2VSi films have been deposited on silicon substrates with an 18 nm silver seed layer and a 3 nm aluminium capping layer using a sputtering system. The best quality film is obtained for 723 K growth. The Mn2VSi thin film is verified to be antiferromagnetic, where an exchange bias is found when a 3 nm ferromagnetic CoFe layer has been deposited on the top of the Mn2VSi layer. The exchange bias is measured to be 34 Oe at 100 K. The blocking and thermal activation temperature (TACT) of Mn2VSi is estimated to be below 100 K and within a range between 100 K and 448 K, respectively. These properties can be improved by substituting the constituent atoms with the other elements (e.g., Co and Al), suggesting a potential of Mn2VSi to be used as an antiferromagnet in a spintronic device

Low-temperature crystallisation of Heusler alloy films with perpendicular magnetic anisotropy

We demonstrate that perpendicular anisotropy can be induced in Co2FeAl0.5Si0.5 by depositing the Heusler alloy on a tungsten seed layer. This is increased by elevating the deposition temperature to a moderate value up to 335 K. These perpendicular layers can be implemented into GMR devices, showing layer-thickness dependent switching without the use of an antiferromagnetic pinning-layer. These layers can be implemented into the manufacturing process of read-heads, where temperatures are limited

Integration of antiferromagnetic Heusler compound Ru2MnGe into spintronic devices

We report on the integration of an antiferromagnetic Heusler compound acting as a pinning layer into magnetic tunneling junctions (MTJs). The antiferromagnet Ru2MnGe is used to pin the magnetization direction of a ferromagnetic Fe layer in MgO based thin film tunneling magnetoresistance stacks. The samples were prepared using magnetron co-sputtering. We investigate the structural properties by X-ray diffraction and reflection, as well as atomic force and high-resolution transmission electron microscopy. We find an excellent crystal growth quality with a low interface roughnesses of 1–3 A ̊ , which is crucial for the preparation of working tunneling barriers. Using Fe as a ferromagnetic elec- trode material, we prepared magnetic tunneling junctions and measured the magnetoresistance. We find a sizeable maximum magnetoresistance value of 135%, which is comparable to other common Fe based MTJ systems

Thermal stability of exchange bias systems based on MnN

At the present time there is a requirement to identify new antiferromagnetic alloys or compounds which might be suitable for the production of exchange bias systems. The phenomenon of exchange bias remains crucial for the operation of all read heads in hard disk drives and also has potential for use in magnetic random access memory (MRAM) systems. There is also an increasing interest in the use of antiferromagnets themselves in spintronic devices. Generally for applications the alloy IrMn is used, however given that Iridium is one of the rarest, and therefore most expensive elements on Earth, there is a search for alternative materials. In this paper we report on a study of the compound MnN in terms of its thermal stability. We have produced polycrystalline films of this compound with sub 10 nm grains and examined the thermal stability in layers of thicknesses of up to 30 nm. Using thermal activation studies we have determined a room temperature value of the anisotropy constant of this compound in a tetragonal structure of up to (6.3 ± 0.3) × 10 6 erg/cm 3 . The antiferromagnetic grains can be aligned by thermal annealing at an optimum temperature of 380 K. Above this temperature the magnetic properties deteriorate possibly due to nitrogen desorption

Structural and antiferromagnetic characterization of noncollinear D019 Mn3Ge polycrystalline film

Distorted Heusler compound of D019 Mn3Ge polycrystalline films were studied in terms of their crystalline structures and antiferromagnetic behavior by varying annealing temperature and Mn-Ge composition. Although low temperature growth for 30 nm Mn3Ge showed no diffraction peaks in X-ray diffraction patterns, high temperature growth over 773 K with Mn-rich composition is found to promote the (0001) orientation of D019 Mn3Ge which resulted in the emergence of an exchange bias effect in Co0.6Fe0.4 ferromagnetic layer at 120 K. The exchange bias field of 12 Oe in Mn3.16Ge film grown at 773 K were improved to 61 Oe by enriching Mn composition to Mn3.97Ge. The average blocking temperature was measured to be at 150 K which is not as high as its reported Néel temperature of 390 K in the bulk state, however, further improvements are expected by doping additional transition elements

Current-induced crystallisation in Heusler alloy films for memory potentiation in neuromorphic computation

The current information technology has been developed based on von Neumann type computation. In order to sustain the rate of development, it is essential to investigate alternative technologies. In a next-generation computation, an important feature is memory potentiation, which has been overlooked to date. In this study, potentiation functionality is demonstrated in a giant magnetoresistive (GMR) junction consisting of a half-metallic Heusler alloy which can be a candidate of an artificial synapse while still achieving a low resistance-area product for low power consumption. Here the Heusler alloy films are grown on a (110) surface to promote layer-by-layer growth to reduce their crystallisation energy, which is comparable with Joule heating induced by a controlled current introduction. The current-induced crystallisation leads to the reduction in the corresponding resistivity, which acts as memory potentiation for an artificial GMR synaptic junction

Fabrication of magnetic tunnel junctions with a metastable bcc Co3Mn disordered alloy as a bottom electrode

We fabricated MgO barrier magnetic tunnel junctions (MTJs) with a Co3Mn alloy bottom and FeCoB top electrodes. The (001)-oriented epitaxial films of the metastable bcc Co3Mn disordered alloys obtained showed saturation magnetization of approximately 1640 emu/cm3. The transmission electron microscopy showed that the MgO barrier was epitaxially grown on the Co3Mn electrode. Tunnel magnetoresistance of approximately 150% was observed at room temperature after the annealing of MTJs at 350◦C, indicating that bcc Co3Mn alloys have relatively high spin polarization

Review on Spintronics : Principles and Device Applications

Spintronics is one of the emerging fields for the next-generation nanoelectronic devices to reduce their power consumption and to increase their memory and processing capabilities. Such devices utilise the spin degree of freedom of electrons and/or holes, which can also interact with their orbital moments. In these devices, the spin polarisation is controlled either by magnetic layers used as spin-polarisers or analysers or via spin-orbit coupling. Spin waves can also be used to carry spin current. In this review, the fundamental physics of these phenomena is described first with respect to the spin generation methods as detailed in Sections 2 ~ 9. The recent development in their device applications then follows in Sections 10 and 11. Future perspectives are provided at the end