Recently considerable attention has been paid to study of domain wall propagation in nanoand microwires because the ability to control this propagation can be used for creation of new type of memory and coding system. The understanding of the possibilities to manipulate the domain wall propagation and to achieve the highest velocities of domain wall propagation is very important for these applications. It was found the time and temperature of annealing have different effects on each of the two types of investigated microwires. Domain wall velocity enhances for one group of microwires and decreases for second group under increasing of the annealing time. Such distinction in domain wall dynamics were discussed in terms of stresses and defects presented in microwires.

We showed that domain wall velocity and the field range for single domain wall propagation can be considerably enhanced under certain annealing conditions for some samples (for example, for glass coated microwires with Co56,8Fe6,2Ni10B16Si11 metallic core). We have studied magnetic and structural properties of the composite microwires consisted of the metallic core and the outer glass shell. Nominal chemical composition of the core was Ni49.5Mn25.4Ga25.1, its diameter was 13.2 mkm, and the total diameter of the glass-covered microwires was 26.4 mkm. We have found out that at room temperature the core of the as-cast microwires was composed by two phases with tetragonal I4/mmm and cubic Fm3m crystal structures, but annealing rendered it single phase. Measurements of the magnetic properties have demonstrated substantial growth of the magnetic anisotropy with cooling, which we have attributed to the phase transition from the room-temperature austenitic to the low-temperature martensitic state. Magnetic easy axis was found to be perpendicular to the axis of the microwires at low temperatures. We believe that it is a result of the crystallographic texture induced in the martensite by high internal stress characteristic of the glass-covered magnetic microwires. Though rearrangement of the martensitic microstructure under external pressure was previously observed in the single crystal Ni2MnGa samples, in composite materials this effect is new and can be potentially useful for the applications.

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V. Rodionova, K. Chichay, S. Shevyrtalov, A. Omelianchik, V. Belyaev, I. Baraban, K. Gritsenko

1) Laboratory of novel magnetic materials, STP “Fabrika”, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

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Correspondence to: rodionova@lnmm.ru

Immanuel Kant Baltic Federal University,

Gaidara 6, Kaliningrad, 236022, Russia

Magnetoelectric (ME) effect is realized in composite structures that consist of ferromagnetic and piezoelectric layers, which are mechanically connected to each other. This effect is the electric polarization of the sample when it is placed in an external magnetic field. It is realized in composite structures through a combination of magnetostrictive ferromagnetic layer and piezoelectric effect of the piezoelectric layer. Such structures are widely used for the development of different devices: high sensitive sensors of the magnetic fields, energy independent sources and so on [1]. The most important tasks are improving the efficiency of the ME interaction and increasing the operating temperature of the structures. These aims are needed improving manufacturing technology structures. The biggest part of layered structures are made by bonding layers by an epoxy adhesive. However, while temperature increase, the value of the ME effect in bonded structures falls because of soften the adhesive and the difference of the temperature coefficients of expansion of the magnetic and piezoelectric layers. Also magnetic and elastic properties of the layers of the structure change [2]. High-temperature soldering is a solving of this problem improving ME characteristics of structures. At first, we need investigate the effect of high temperature annealing on the magnetic properties of ferromagnetic and magnetostrictive layers, which is devoted this work. The work also studied the effect of annealing on the value of the ME effect a 2-layers structures comprising annealed ferromagnetic layer.

[1] Nan C.-W., Bichurin M.I., Dong S., Viehland D., and Srinivasan G. Journal of Applied Physics. 2008. v. 103. № 031101.

[2] D.A. Burdin, et al. JMMM Vol. 358–359, (2014), pp. 98–104

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I.Baraban^1,2, F.Fedulov³, L.Fetisov³, K.Chichay^1,2, V.Rodionova^1,2
1) Laboratory of novel magnetic materials, STP “Fabrika”, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
3) Moscow Technological University, 119454, Moscow, Russia

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Correspondence to: machay@lnmm.ru

Immanuel Kant Baltic Federal University,

Gaidara 6, Kaliningrad, 236022, Russia

The investigation of magnetization dynamics in nano- and micro- objects is of a great interest due to its prospects in development of novel magnetic memory and logic devices [1-3]. Such devices can be implemented on the fast domain wall motion. The highest domain wall velocity, up to 8000 m/s, has been obtained in bistable glass coated amorphous ferromagnetic microwires [2-4]. Besides amorphous state the distinguishing feature of these microwires is the presence of internal stresses, which together with magnetostriction result in a significant effect on the magnetoelastic energy and thereby define the micromagnetic structure and reversal magnetization process.

In our work we considered separate and combined influence of the parameters determining the dynamics of the domain wall to provide for the first time the complex analysis and to find the ways to predict the remagnetization properties. We investigated series of Fe-, FeCo- and FeCoNi-based microwires with the ratio between the metallic nucleus diameter and the total diameter of microwires in glass shell ranging from 0.13 to 0.9, that vary considerably the value and distribution of internal stresses. The magnetic and magnetostrictive properties were investigated for all samples using induction and small angle rotation magnetization methods, respectively. The velocity of the domain wall was measured by Sixtus-Tonks technique. To estimate the micromagnetic structure and reversal magnetization features we investigated an angle dependence of the magnetic properties using vibrating sample magnetometer and field dependence of the perpendicular to the magnetic field component of the magnetic moment using vibrating sample anisometer. We established the correlation between value of internal stresses, axially magnetized core and velocity of the domain wall.

We showed that one of the effective ways to control the magnetic properties and the domain wall dynamics is an annealing. Annealing of Fe-based microwires result in increase the domain wall velocity up to 1.6 times. Annealing of Co_68.7Fe₄Ni₁B₁₃Si₁₁Mo_2.3 microwires, which in as-cast state had S-shape hysteresis loop, under applied stresses leads to dramatic changes of micromagnetic structure and magnetization reversal process – after annealing the microwires become bistable. The range of switching field is strongly depending on the annealing conditions, and hence, can be manipulated easily. This makes such microwires a promising candidate for the development on their base the novel devices.

[1] Katsuaki Sato, Eiji Saitoh, Spintronics for Next Generation Innovative Devices, John Wiley &Sons, Ltd., 2015.

[2] A. Zhukov, Novel Functional Magnetic Materials: Fundamentals and Applications, Springer, 2016

[3] M. Vazquez, Handbook of Magnetism and Advanced Magnetic Materials 4: Novel Materials. John Wiley &Sons, Ltd., 2007.–P.2192-2226.

[4] Varga R., Klein P., K. Richter, Zhukov A., Vazquez M., Fast domain wall dynamics in amorphous and nanocrystalline magnetic microwires, JMMM 324, 3566-3568, 2012

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K. Chichay^{1, 2}, V. Rodionova^{1, 2}, V. Zhukova^3,4, N. Perov⁵, A. Zhukov^{3, 4}

1) Laboratory of novel magnetic materials, STP “Fabrika”, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

3) Dpto. Fisica de Materiales, Fac. Quimicas, UPV/EHU, 20018 San Sebastian, Spain

4) IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

5) Faculty of physics, Lomonosov Moscow State University, Moscow, Russia

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Correspondence to: ks.chichay@gmail.com

Immanuel Kant Baltic Federal University,

Gaidara 6, Kaliningrad, Russia

  The exchange bias phenomenon is a hot topic of investigations thanks to its wide applicability in spintronics, magnetic sensorics, MRAM etc. The exchange bias is a shift of a hysteresis loop along the field axis, revealing an exchange coupling between ferromagnetic (F) and antiferromagnetic (AF) materials at their interface. Each parameter of thin film and its preparing has influence on both the exchange bias value and coercive force, that is shown in many papers [1-3]. We investigated the coercivity and the exchange bias fields as a function of AF-layer thickness and layers deposition sequence in structures Si/Ta/NiFe/IrMn/Ta, Si/Ta/IrMn/NiFe/Ta and Si/Ta/NiFe/ IrMn/NiFe/Ta. It was obtained the critical thickness of IrMn layer for the appearance of the exchange bias. Also it was shown the separation of loops of trilayered films for top and bottom parts, that we can correspond for remagnetization of two interfaces. The dependences of the exchange bias and coercive force on the antiferromagnetic layers thickness in all samples were obtained.

[1] Mishra S. K., Radu F., Durr H. A. and Eberhardt W., 2009, PHYSICAL REVIEW LETTERS, 102, 177208

[2] Ledue D., Maitre A., Barbe F., Lechevallier L., 2014, Journal of Magnetism and Magnetic Materials 324

[3] Zhang T. and Dressel M., 2009, PHYSICAL REVIEW B80, 014435

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Ch. Gritsenko^1,2, I. Dzhun³, G. Babaytsev³, N. Chechenin³, V. Rodionova^1,2

1) Laboratory of Novel Mgnetic Materials, STP “Fabrika”, Immanuel Kant Baltic Federal University, Kaliningrad, Russia, 236022

2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia, 236022

3) Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia, 119991

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Correspondence to: christina.byrka@gmail.com

Laboratory of Novel Magnetic Materials, STP “Fabrika”, IKBFU,

Gaidara, 6, Kaliningrad, Russia, 236022

  Ferrofluids are using worldwide in different application, thus investigation of magnetic properties of ferrofluids is an important task of modern science. One of the ways of using the ferrofluids is biomedicine. In this case, ferrofluids can be used both for diagnosis and treatment in different ways: as a contrast agent in MRI, magnetic hyperthermia, drug delivery and others [1]. In this work, a series of procedure for the preparation of liquid samples for SQUID measurements will be presented. In particular, plastic capsules of ferrofluids of magnetite nanoparticles dispersed in water have been prepared and tested in different temperature environments in order to check their stability after thermal stress. Then, the basic magnetic characterization of their magnetic properties in terms of Zero Field Cooling (ZFC) – Field Cooling (FC), Isothermal Remanent Magnetization (IRM) and Direct Current Demagnetization (DCD) [2] has been carried for ferrofluids with different pH-level [3].

[1] J. Estelrich et al. Int. J. Mol. Sci. 16 (2015) 8070

[2] D. Peddis et al. Nanomagnetism: Fundamentals and Applications Vol. 6. (2014) 138

[3] E. Illés, E. Tombácz, Journal of Colloid and Interface Science 295 (2006) 115–123

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Alexander Omelyanchik^1,2, Erzsébet Illés⁴, Sara Laureti³, Gaspare Varvaro³, Valeria Rodionova^1,2, Ana Mrakovic⁴, Vladan Kusigerski⁴, Vojislav Spasojevic⁴, Sanja Vranjes-Djuric⁴, Nikola Knezevic⁴ and Davide Peddis^3,4

1) Laboratory of novel magnetic materials, STP “Fabrika” Immanuel Kant Baltic Federal University, Kaliningrad, Russia

2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

3) Istituto di Struttura della Materia– CNR, 00016 Monterotondo Stazione, Roma, Italy

4) Dept. of Theoretical and Condensed Matter Physics, Vinča Institute of Nuclear Sciences, Belgrade, 11001, Serbia

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Correspondence to: 9azazel@gmail.com

Immanuel Kant Baltic Federal University,

Nevskogo 14a, Kaliningrad, 236004, Russia.

Magnetic shape memory alloys (MSMA) receiving big attention due to their unique properties related with martensitic transformation [1]. This transformation described as temperature-induced first order phase transition from high-temperature high-ordered austenitic phase (L21 cubic) to a lowtemperature martensitic phase with lower symmetry (modulated orthorhombic, tetragonal). For thin film MSMA structures, one of the crucial parameter is the substrate. Since, the martensitic transition is followed by drastic change in lattice parameters, the transition can be interrupted by kinetic arrest [2]. So, the substrate impact on transformation should be clarified. Ni-Mn-Ga Heusler alloy thin films were grown on Al₂O₃ substrate using magnetron sputtering method. Thin films with 100, 200, 400 nm and 1, 2 um thicknesses have been prepared from Ni₅₄Mn₂₀Ga₂₆ ingot. Chemical concentration varies a little bit with film thickness. To form the crystallographic structure samples were annealed in vacuum furnace at 1073 K for 1 hour. Fm-3m phase were detected at room temperature using XRD analysis for all annealed samples. We should notice that no Ni-Mn-Ga phase have been obtained for as-prepared samples. Thermomagnetic curves M(T) were measured using SQUID magnetometer in magnetic field of 10 Oe and 10 kOe in temperature range of 100-400 K for annealed samples and for as-prepared samples with thicknesses of 100 nm and 1 um to comparison. In addition, to match the results we also conducted DSC measurement for samples with 100 nm and 1um thicknesses at the same temperature range. To complete the research resistance vs temperature curves were collected in temperature range of 100-400 K in magnetic field of 10 Oe and 10 kOe for both as-prepared and annealed samples. Based on the obtained data the influence of the Al₂O₃ substrate were clarified.

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S. Shevyrtalov^1,2, V. Khovaylo^3,4, Eijiro Abe⁵, Hiroyuki Miki⁶, V. Rodionova^1,2

1) Laboratory of novel magnetic materials, STP “Fabrika”, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia

3) National University of Science and Technology MISiS, Moscow, Russia

4) ITMO University, St. Petersburg, Russia

5) Graduate School of Engineering, Tohoku University, Sendai, Japan

6) Frontier Research Institute for Interdisciplinary Sciences (FRIS), Tohoku University, Sendai, Japan

Surface Plasmon Resonance (SPR) sensors are widely used for different applications [1] and the main task in this sphere is increasing of the sensitivity. One of the ways – is adding an additional type of modulation, for example, by magnetic field. Typical SPR sensors consists of noble metal/dielectric materials and appreciable modulation can be reached in magnetic fields up to several tesla. The other way is using magneto-optical (MO) effects. It is possible to combine both of these ways by using the magnetoplasmonic crystals (MPlCs) – multilayer structures fabricated of noble and ferromagnetic layers on substrate with certain spatial profile [2-3]. This way can demonstrate that it is possible both to enhance the MO activity of the system by surface plasmon excitation, and to modulate the surface plasmon properties by application the external magnetic field [4]. Possibility of fabrication of AC and DC magnetic fields sensor based on MPlCs and the way of tuning sensitivity and working fields range are demonstrated.

[1] Grunin A., Zhdanov. A., Fedyanin A., Appl. Phys. Lett. 97, 261908, (2010)

[2] Belotelov V., Akimov. I, Bayer M., Nat. Nanotechnol 6, 370, (2011)

[3] Belyaev V., Grunin A., Fedyanin A., Rodionova V, SSP, Vols 233-234, pp. 599-602, (2015)

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V.K. Belyaev^1,2, A.A. Grunin³, A.A. Fedyanin³, V.V. Rodionova^1,2

1) Laboratory of novel magnetic materials, STP “Fabrika” Immanuel Kant Baltic Federal University, Kaliningrad, Russia
2) FunMagMa, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
3) Lomonosov Moscow State University, Moscow, Russia

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Correspondence to: belyaev@lnmm.ru

Immanuel Kant Baltic Federal University,

Gaidara 6, Kaliningrad, 236022, Russia