Seminar Festkörper- und Grenzflächenphysik

Programm für das Wintersemester 2019/2020

Tuesdays, 12:00 Uhr s.t.

Prof. Dr. H. J. Elmers

Ort: Institut für Physik, Newton-Raum, Staudingerweg 9, 1. Stock, Raum 122 (Nebengebäude)

06.12.19Akashdeep Ghalayan, Indian Institute of Technology Delhi, India
Heusler Alloys have been widely studied due to their potential applications in spintronic devices. Understanding the material's magnetic properties is crucial for deciding its device-based applications. Heusler alloys with high spin polarization (~100 %) and high Curie temperature (~1000 K) are one of the most preferred materials in this regard. The cobalt-based Co2MnAl (CMA) Heusler alloys exhibit more than 50% spin polarization even in the disordered phase with high Curie temperature (Tc ~ 697 K) which is beneficial for device applications. Thin films of CMA with different Co-Mn concentrations have been grown using DC magnetron sputtering at constant growth temperature (Ts ~ 400°C) and film thickness (~ 50 nm) to investigate the effect of Co/Mn concentrations on their electrical transport behavior. X-ray diffraction studies revealed that films possess the A2 disordered phase at room temperature. Magnetic anisotropy, which is vital for magnetic switching device applications, has been investigated using the Longitudinal Magneto-Optic Kerr Effect technique. LMOKE studies revealed the presence of uniaxial magnetic anisotropy in these films. The origin of the uniaxial anisotropy in our films is attributed to obliquely directed material flux onto the substrates during the film-growth.

Sonderseminar

10.12.19Alexander Tries, Inst. f. Physik
tba

17.12.19Mariia Filianina, Inst. f. Physik
Electric field-induced strain control of magnetism in in-plane and out-of-plane magnetized thin films

13.01.20Abhishek Erram , Indian Institute of Technology Kharagpur
In this work, we have made a polycrystalline sample of Dy2BaNiO5 by a standard solid-state reaction route. The formation of the compound was ascertained by x-ray powder diffraction pattern. The dc χ measurements were carried out in the temperature interval 5–300 K in the presence of magnetic fields of 100 Oe and 5 kOe for zero-field-cooled (zfc) and field-cooled (fc) conditions using (SQUID) and isothermal magnetization (M) behavior was studied at a certain selected low temperature. Then, Thin film of Dy2BaNiO5 certain thickness were deposited on Mgo , Al203 ,STO and LAO substrate by Pulsed Layer Deposition method these films were annealed at temperature 650 oC. Some of the samples were Characterized by X-ray diffraction (XRD). Magnetic behavior was also studied. Results show that of formation of thin film. Signs of magnetic behavior was also evident.

Sonderseminar

21.01.20Olga Lozhkina, Inst. f. Physik
tba

24.01.20Mona Minakshee Manjaree Bhukta , National Institute of science education and research, Bhubaneswar, India
1.Thermal diffusion of nπ Skyrmion and Skyrmion bags Skyrmionics have recently emerged as active field of research because of their potential applications in high density data storage technology and logic gate computing. Magnetic skyrmions correspond to localized whirling spin configurations, which are characterized by a topological charger (Q). Recent atomistic simulations and experimental finding ensure the diffusive behaviour of skyrmion at finite temperatures in ultrathin model, which open up the possibility of application thermal induced skyrmion dynamics in probabilistic computing. In this work we studied the thermal diffusion of nπ skyrmion up to n= 5 and N skyrmion bag (N (= 1-6) skyrmion surrounded by a bigger skyrmion with opposite chirality) using atomistic spin simulation on Pt_{0.95}/Ir_{0.05} on Pd (111) bilayer by statistically averaging out 100s of these spin texture. Further the SkHE of all these structures has been calculated using both simulation and analytics. 2.Frustrated Skyrmionic States in synthetic Antiferromagnet The spherical topology of a skyrmion leads to an extra force, that acts on moving skyrmion, pointing perpendicular to its velocity. This deviates the path of the skyrmion towards the edge of the nanotrack and this phenomenon is referred as the Skyrmion Hall effect (SkHE). In an antiferromagnetically exchange-coupled bi-layer nanotrack, this SkHE could be suppressed without affecting the topological protection of the skyrmion. Recently it is shown that skyrmion in frustrated ferromagnets have more helicity and vorticity degrees of freedom in compared with the skyrmion stabilized by Dzyaloshinskii-Moriya Interaction (DMI). In this work, we attempted to model a system using micromagnetic simulation to induce frustration by taking RKKY interaction as perturbation in a Synthetic antiferromagnet (SAF). The frustration in the system could be due to the equivocation of DMI between two antiferromagnetically coupled layer. We not only found the existence of Q = 0 skyrmion, but also able to stabilize the skyrmion and antiskyrmion in the same layer. Later we deposited Ta/(Pt/Co)_2/Ir(x)/Co/Pt (x= 0.5 and 1.0 nm) on Silicon substrate using DC magnetron sputtering to optimize the SAF nature of the thin films and to observe the domain images using Kerr Microscope.

28.01.20Stanislav Bodnar, Inst. f. Physik
Manipulation of Néel vector in antiferromagnetic Mn2Au by current and magnetic field pulses

04.02.20Amrit R. Pokharel, Inst. f. Physik
Carrier relaxation dynamics in Kondo insulator YbB12

06.02.20Kelvin van Hoorn, Technical University of Eindhoven, The Netherlands
Magnetic field sensors based on deflection of membranes

Sonderseminar

07.02.20Chi Fang, University of Chinese Academy of Sciences, Beijing, China
The application potential of spin-orbit-torques in magnetic random access memory attracts great attention and research interest in spin-orbit coupling in heavy metals like Platinum and Tantalum. Thus the spin relaxation time τ_s, as a crucial parameter to investigate spin relaxation mechanism in the heavy metals, requires accurate and effective estimation. A traditional three-terminal method is also widely utilized to estimating τ_s of semiconductors and light metals. Its reliability, however, has recently been challenged by some experiments in which tunneling anisotropic magnetoresistance (MR) or spin blockage MR rather than the MR induced by spin injection and subsequent Hanle effect is more appropriate to explain the data. In this talk, I will introduce the spin-injection-induced magnetoresistance of which the magnitude is comparable with other MR phenomena originating from the tunnel barrier is observable at room temperature as well as low temperatures in the second harmonic signals. Three-terminal and second harmonic method are combined in our measurement in Pt and Ta systems. Furthermore, we could estimate τ_s of heavy metals through fitting the signal with Lorentz function. This experimental approach make it possible to directly acquire τ_s of heavy metals with electrical method.

Sonderseminar

19.02.20Dr. Kunie Ishioka, National Institute for Materials Science, Tsukuba, Japan
Mittwoch, den 19. Februar 2020 um 14:30 im MEDIEN-Raum, Staudinger Weg 7, 03-431 Ultrafast Carrier and Phonon Dynamics of Hybrid Lead Halide Perovskite Kunie Ishioka National Institute for Materials Science, Tsukuba, Japan Inorganic-organic hybrid lead halide perovskites, consisting of the soft lead halide octahedral framework and the organic molecular cations, are among the key materials for the next generation photovoltaics. In the first half of my talk I present on the charge separation dynamics at the interfaces of methylammonium lead iodide MAPbI3 with three different hole transport materials (HTMs) [1]. Here, the differential transmission signals revealed the hole injection from the perovskite to organic HTMs to occur on the time scale of 1 ps, whereas that to inorganic NiOx on an order of magnitude longer timescale. The anti-correlation with the fill factor of the solar cells suggests that the interfacial quality was responsible. In the second half I present our recent results on the coherent phonons of MAPbI3 [2]. We observe periodic modulations in the transient transmissivity due to the photoinduced libration and torsion of the methylammonium cations and the deformation of the PbI6 octahedral framework. The frequencies of the cation torsion and the octahedral deformations exhibited downchirps, in agreement with theoretically predicted strong anharmonicities of their vibrational potentials.

Sonderseminar

Sondertermin

13.03.20Jonas Knobel, Universität Würzburg
New directions in spintronics heading towards devices based on antiferromagnetic materials require a fundamental understanding of the underlying physics. CuMnSb grown by molecular beam epitaxy (MBE) on GaSb substrates can provide a model system of a thin film antiferromagnet. I will report on the growth of virtually unstrained pseudomorphic single crystals showing clear antiferromagnetic behavior. The ordering temperature of CuMnSb between 50K and 62K lies well within the reach of standard cryostats. This allows to diff erentiate thermal from magnetic properties in transport devices. I will first discuss the epitaxial growth of a GaSb buff er layer needed for a sharp interface. Subsequent CuMnSb growth is highly dependent on the flux ratios of the respective elements. I will explain their influence on crystal properties and how reflection high-energy electron di ffraction (RHEED) is used to control the growth process.

Sonderseminar

13.03.20Kanji Furuta, Department of Materials Science and Engineering, Nagoya University, Japan.
MAX phase compounds have recently attracted much attention due to their possible application to the production of a new class of two-dimensional systems called MXenes [1]. Mo4Ce4Al7C3 is affiliated with the MAX phase and in a family of RE-based nanolaminates with a chemical formula of Mo4RE4Al7C3. From magnetization measurements, x-ray absorption near-edge structure (XANES), and x-ray magnetic circular dichroism (XMCD), a ferromagnetism below a Curie temperature of TC ~ 10.5 K and a mixed-valence states of the Ce 4f electrons have been reported [2]. To understand the origin of electronic/magnetic properties of Mo4Ce4Al7C3, we have performed angle-resolved photoemission spectroscopy (ARPES) on Mo4Ce4Al7C3 single-crystals. As a result, we have succeeded to obtain the electronic band structure as well as Fermi surface of this system. From the comparison between Ce 4d-4f on and off resonant ARPES, strong Ce 4f character at the electron pocket around the G point has been elucidated. Furthermore, we have found a clear increase of the Ce 4f spectral weight below TC. The results suggest that itinerant Ce 4f electrons may play an important role in the magnetic properties of Mo4Ce4Al7C3. REFERENCES [1] M. Barsoum, MAX phases (Wiley, Weinheim, 2013). [2] Q. Tao et al., Phys. Rev. Mat. 2, 114401 (2018).

Sonderseminar

Koordination: Kontakt:

Prof. Dr. Hans-Joachim Elmers
Institut für Physik, KOMET 335
elmers@mail.uni-mainz.de

Daniela Reibel-ElBatanony
reibel@uni-mainz.de