Ab initio to application: antiferromagnetic Heusler compounds for spintronics

Balluff J. Ab initio to application: antiferromagnetic Heusler compounds for spintronics. Bielefeld: Universität Bielefeld; 2017.Antiferromagnetic materials play a key role in the field of spintronics. The exchange bias, which pins the magnetic orientation of a ferromagnet which is in contact with an antiferromagnet, is utilized to create a magnetic reference for spintronic devices such as magnetic tunneling junctions. This work deals with the theoretical search for novel antiferromagnetic compounds among the Heusler family, a versatile, ternary material class. Experimental work on selected compounds verifies theoretical predictions and demonstrate working devices based on antiferromagnetic Heusler compounds

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

CRIP1 expression is correlated with a favorable outcome and less metastases in osteosarcoma patients

Predicting the clinical course of osteosarcoma patients is a crucial prerequisite for a better treatment stratification in these highly aggressive neoplasms of bone. In search of new and reliable biomarkers we recently identified cysteine-rich intestinal protein 1 (CRIP1) to have significant prognostic impact in gastric cancer and therefore decided to investigate its role also in osteosarcoma. For this purpose we analyzed 223 pretherapeutic and well characterized osteosarcoma samples for their immunohistochemical expression of CRIP1 and correlated our findings with clinico-pathological parameters including follow-up, systemic spread and response to chemotherapy. Interestingly and contrarily to gastric cancer, we found CRIP1 expression more frequently in patients with long-term survival (10-year survival 73% in positive vs. 54% in negative cases, p = 0.0433) and without metastases (p = 0.0108) indicating a favorable prognostic effect. CRIP1 therefore seems to represent a promising new biomarker in osteosarcoma patients which should be considered for a prospective validation

Development of Antiferromagnetic Heusler Alloys for the Replacement of Iridium as a Critically Raw Material

As a platinum group metal, iridium (Ir) is the scarcest element on the earth but it has been widely used as an antiferromagnetic layer in magnetic recording, crucibles and spark plugs due to its high melting point. In magnetic recording, antiferromagnetic layers have been used to pin its neighbouring ferromagnetic layer in a spin-valve read head in a hard disk drive for example. Recently, antiferromagnetic layers have also been found to induce a spin-polarised electrical current. In these devices, the most commonly used antiferromagnet is an Ir-Mn alloy because of its corrosion resistance and the reliable magnetic pinning of adjacent ferromagnetic layers. It is therefore crucial to explore new antiferromagnetic materials without critical raw materials. In this review, recent research on new antiferromagnetic Heusler compounds and their exchange interactions along the plane normal is discussed. These new antiferromagnets are characterised by very sensitive magnetic and electrical measurement techniques recently developed to determine their characteristic temperatures together with atomic structural analysis. Mn-based alloys are found to be most promising based on their robustness against atomic disordering and large pinning strength up to 1.4 kOe, which is comparable with that for Ir-Mn. The search for new antiferromagnetic films and their characterisation are useful for further miniaturisation and development of spintronic devices in a sustainable manner

High-throughput screening for antiferromagnetic Heusler compounds using density functional theory

Balluff J, Diekmann K, Reiss G, Meinert M. High-throughput screening for antiferromagnetic Heusler compounds using density functional theory. PHYSICAL REVIEW MATERIALS. 2017;1(3): 034404.Commonly used antiferromagnets contain expensive precious metals, which limits their applicability. Novel materials that are made of abundant elements are thus required for a large scale application, e.g., in spintronic devices. We propose a combinatorial, high-throughput approach based on density functional theory calculations to search for such new antiferromagnets. The power of the method is demonstrated by screening the ternary Heusler compounds for antiferromagnetic phases. We utilize the AFLOWLib, a computational materials database that contains over one million ternary phases. Among these we identify 291 potentially stable magnetic Heusler compounds. By explicitly checking for antiferromagnetic configurations we identify 70 antiferromagnetic Heusler compounds. Comparison with available experimental data shows that the method has excellent selectivity: all known antiferromagnetic Heusler compounds are correctly identified and no material is erroneously assigned an antiferromagnetic ground state. By calculating the Neel temperatures we predict 21 antiferromagnetic Heusler compounds with a Neel temperature above room temperature

Exchange bias in epitaxial and polycrystalline thin film Ru2MnGe/Fe bilayers

Balluff J, Meinert M, Schmalhorst J-M, Reiss G, Arenholz E. Exchange bias in epitaxial and polycrystalline thin film Ru2MnGe/Fe bilayers. Journal of Applied Physics. 2015;118(24): 243907.We report on thin film bilayers of the antiferromagnetic Heusler compound Ru2MnGe and Fe, as well as the resulting exchange bias field at low temperatures and its temperature dependence. Epitaxial Ru2MnGe/Fe bilayers show an exchange bias field up to 680Oe at 3K. For increasing temperatures, a linearly decreasing exchange bias field is found, which vanishes at 130K. Furthermore, we grew polycrystalline Ru2MnGe showing an exchange bias field up to 540 Oe, which vanishes around 30K. By adding a very thin intermediate layer of Mn, the exchange bias field for polycrystalline samples has been increased by about 40%. We discuss differences between the epitaxial and polycrystalline films regarding magnetic and crystallographic properties and compare our results to already published work on this system. (C) 2015 AIP Publishing LLC

Enhancing magnetic properties in Mn3Ge thin films by doping

The ferrimagnetic Mn3Ge compound has appealing properties for spintronic applications, e.g., a low saturation magnetization, and often a large coercive field is found. Here, we report on a combined experimental and theoretical approach to both reduce the magnetization and increase the coercivity of Mn3Ge by doping. By calculating defect formation energies, we predict several dopants that are expected to specifically occupy only one lattice site of the crystal structure. For Ni as a dopant, we predict a reduction in the magnetization, which we verify by preparing thin film samples by magnetron co-sputtering. We confirm the predicted reduction in magnetization as well as a greatly enhanced coercivity of more than 5 T. To improve the understanding of the sublattice magnetization in the doped ferrimagnetic material, we performed magnetic spectroscopy experiments on selected samples and compared the results with calculated data. An important finding from a detailed analysis of the spectroscopic data is that a frequently observed soft contribution in the magnetization loop arises from impurities in the film

A Machine Learning Approach to Enterprise Matchmaking Using Multilabel Text Classification Based on Semi-structured Website Content

Finding the right business partner to drive innovation or acquire technology transfer is a labor and time-intensive process. To simplify this process, there is a need for improved methods of automated matchmaking that can quickly identify the best potential collaboration partners. This paper presents a novel approach for semi-automated business matchmaking between companies and research institutes, that is applied to a first case study. For this purpose, we compare two transformer-based text classification models and evaluate how dataset quality affects few-shot learning performance. Flair's TARS classifier performed very well in our use case, requiring only 40 examples per class to achieve an F1 score of about 90%. This is already very close to the Hugging Face standard text classifier, which achieved an F1 score of 92% with much more annotation effort. The results show that few-shot learning models like TARS can achieve accurate results even with few training samples compared to regular transformer-based language models. Our novel approach allows the time-consuming and labor-intensive task of manual partner matchmaking to be significantly reduced

Structural, magnetic, and electrical properties of perpendicularly magnetized Mn4-xFexGe thin films

Niesen A, Teichert N, Matalla-Wagner T, et al. Structural, magnetic, and electrical properties of perpendicularly magnetized Mn4-xFexGe thin films. JOURNAL OF APPLIED PHYSICS. 2018;123(11): 8.We investigated the structural, magnetic, and electrical properties of the perpendicularly magnetized Mn4-xFexGe thin films (0.3 <= x <= 1). The tetragonally distorted structure was verified for all investigated stoichiometries. High coercive fields in the range of 1.61 T to 3.64 T at room temperature were measured and showed increasing behavior with decreasing Fe content. The magnetic moments range from (0.16 +/- 0.02) mu(beta/)f.u for Mn3Fe1Ge to (0.08 +/- 0.01) mu beta/f.u for Mn3.4Fe0.6Ge. X-ray absorption spectroscopy revealed ferromagnetic coupling of the Mn and Fe atoms in Mn4-xFexGe and the ferrimagnetic ordering of the Mn magnetic moments. Anomalous Hall effect measurements showed sharp magnetization switching. The resistivity values are in the range of 207 mu Omega cm to 457 mu Omega cm depending on the stoichiometry. From the contribution of the ordinary Hall effect in the anomalous Hall effect measurements, Hall constants, the charge carrier density, and mobility were deduced. The thermal conductivity was calculated using the Wiedemann-Franz law. All these values are strongly influenced by the stoichiometry. An alternative method was introduced for the determination of perpendicular magnetic anisotropy. The values range between 0.26 MJ/m(3) and 0.36 MJ/m(3). Published by AIP Publishing