Article
Engineering, Electrical & Electronic
Stephanie Hernandez, Zengyuan Liu, Peiran Jin, Steven D. Granz, Pavol Krivosik, Raman Venkataramani, William Radich, Tim Rausch, John Dykes, Edward C. Gage
Summary: This article presents the system-level requirements for heat-assisted magnetic recording at high areal density, highlighting the importance of spatial SNR, media SNR, reader SNR, and CBD. It discusses the tradeoffs needed to maintain BER as areal density increases, and points out the extremely aggressive geometrical requirements for very high areal density, which may require significant invention in head and drive architecture design.
IEEE TRANSACTIONS ON MAGNETICS
(2021)
Article
Physics, Condensed Matter
F. Magnus, U. B. Arnalds, H. Palonen, G. K. Palsson, H. Ali, K. Leifer, B. Hjorvarsson
Summary: The passage describes the investigation of the magnetic properties of amorphous exchange-spring magnet trilayers, where the coupling between magnetically soft and hard layers can be controlled through temperature. The experiment shows that a magnetic state can be achieved with perpendicular magnetization of the soft layer in the strong coupling regime.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2021)
Article
Engineering, Electrical & Electronic
Pierre-Olivier Jubert, Tiffany Santos, Thanh Le, Burak Ozdol, Cristian Papusoi
Summary: The study explores the relevance of anisotropic heatsinks for HAMR, finding that their performance is determined by in-plane thermal conductivity. TDTR measurements extracted the thermal conductivities of a (Cu/Ta) multilayer heatsink, demonstrating its potential as a candidate for HAMR with high in-plane thermal conductivity.
IEEE TRANSACTIONS ON MAGNETICS
(2021)
Article
Physics, Applied
Wei-Heng Hsu, R. H. Victora
Summary: In heat-assisted shingled magnetic recording, rotating the read head to match the curvature of asymmetrically curved transitions can significantly improve user density. With optimized rotation angle, the user areal density reaches 6.2 Tb/in(2), exceeding previous projections by more than 30%.
APPLIED PHYSICS LETTERS
(2021)
Article
Engineering, Mechanical
Qilong Cheng, David B. Bogy
Summary: This study experimentally investigated the effect of disk temperature and laser exposure time on smear formation in HAMR hard disk drives, and studied the removal of smear through frictional interactions between the head and the disk. The results showed that the smear is mostly removed by friction during head-disk contact, providing a mechanical approach to mitigate smear without damaging the head.
TRIBOLOGY INTERNATIONAL
(2022)
Article
Engineering, Electrical & Electronic
Ali Ghoreyshi, Douglas A. Saunders, Chris J. Rea
Summary: Finite-size scaling is used to study the erasure mechanism in heat-assisted magnetic recording (HAMR) by numerically and experimentally evaluating predicted scaling equations with the write current-assist percentage (WCAP) method. Results show the scaling behavior of erasure temperature with different applied field values and provide estimates for the anisotropy field and critical exponent. The Stoner-Wohlfarth model is found to be an accurate approximation for the erasing process in FePt media.
IEEE TRANSACTIONS ON MAGNETICS
(2021)
Review
Materials Science, Multidisciplinary
Wei-Heng Hsu, R. H. Victora
Summary: Hard disk drives are widely used for mass storage due to their low cost and high capacity. However, current perpendicular magnetic recording technology is reaching its physical limit in terms of areal density capability. To overcome this, heat-assisted magnetic recording (HAMR) has been introduced, which utilizes laser heating to reduce coercivity and record information during the cooling process. Computational micromagnetics is a useful tool for studying the high-temperature magnetization dynamics in HAMR.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Engineering, Electrical & Electronic
Lei Xu, Richard M. Brockie, Niranjan A. Natekar, Eric Roddick
Summary: In this study, we analyze the scaling potential of HAMR and the factors that hinder scaling. We conduct a numerical investigation on various factors, including grain density, thermal spot size, reader dimensions, media velocity, and evaluate their relative importance. The results highlight the criticality of reader, grain density, and thermal spot scaling in realistic HAMR systems, and emphasize the importance of improving the reader by varying its width and head electronic signal-to-noise ratio.
IEEE TRANSACTIONS ON MAGNETICS
(2023)
Article
Engineering, Electrical & Electronic
Hikaru Yamane, Simon John Greaves, Yoichiro Tanaka
Summary: Modeling heat-assisted magnetic recording on bit patterned media dots with two magnetic structures showed that storing two bits of information in each dot is possible. The areal density capability of the dual structure media was calculated to exceed 7 Tbit/in(2) despite dot position distributions and magnetostatic fields from surrounding dots.
IEEE TRANSACTIONS ON MAGNETICS
(2021)
Article
Materials Science, Multidisciplinary
A. Bolyachkin, H. Sepehri-Amin, I. Suzuki, H. Tajiri, Y. K. Takahashi, K. Srinivasan, H. Ho, H. Yuan, T. Seki, A. Ajan, K. Hono
Summary: This study investigates the effects of structural defects on the magnetic properties of FePt-X nanogranular media using transmission electron microscopy (TEM) images and micromagnetic simulations. A new method for evaluating structural defects is developed and validated. The study directly links the nanostructure to the magnetic properties, enabling optimization of heat-assisted magnetic recording (HAMR) media and design of magnetic nanomaterials in general.
Article
Chemistry, Physical
I. Suzuki, H. Sepehri-Amin, K. Hono, Y. K. Takahashi
Summary: In this study, the dependence of grain density and microstructure of FePt-based granular films on the lattice mismatch between the films and various substrates was investigated. It was found that the grain density increased and grain size decreased with increasing lattice mismatch. The optimum lattice mismatch was 8%, while films grown on TiO2 substrate with the largest lattice mismatch of 16% exhibited poor morphology and low grain density.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Engineering, Chemical
Qilong Cheng, Roshan Mathew Tom, David B. Bogy
Summary: Heat-assisted magnetic recording (HAMR) technology uses a laser to assist data writing, but it causes material transfer problem due to temperature difference. This study presents two strategies, mechanical and thermal, to mitigate the material buildup issue. The results are important for the commercialization of HAMR technology.
Article
Forestry
Mariah Casmey, Andreas Hamann, Uwe G. Hacke
Summary: This study examines the differences in heat sum and chilling requirements among different geographic populations of white spruce. The results show significant variations in heat sum requirements among regions and populations within regions, while no geographic differentiation is found for chilling requirements. The study suggests that white spruce can synchronize its phenology with the growing season under climate warming and northward migration can result in higher growth rates.
FOREST ECOLOGY AND MANAGEMENT
(2022)
Article
Energy & Fuels
J. Goertz, J. Juergensen, D. Stolz, S. Wieprecht, K. Terheiden
Summary: Understanding and quantifying the heat fluxes between a civil structure and the environment is crucial for estimating cooling and heating requirements and inhibiting strains. Knowledge about incoming and outgoing heat fluxes is also important in low-energy and passive house design. However, accurately defining heat fluxes is complex. This study aims to improve the understanding and quantification of heat fluxes.
Article
Materials Science, Multidisciplinary
N. Kulesh, A. Bolyachkin, I. Suzuki, Y. K. Takahashi, H. Sepehri-Amin, K. Hono
Summary: The main challenge for HAMR to achieve a potential areal density of 4 Tb/in2 is the difficulty in obtaining FePt-X nanogranular media with an ideal stacking structure. In this study, a fully automated routine combining convolutional neural network and machine vision was developed to mine data from transmission electron microscopy images of FePt-C nanogranular media. This allowed the generation of a dataset and implementation of a machine learning optimization model to guide process parameters, resulting in the desired nanostructure successfully validated experimentally. This work demonstrates the potential of data-driven design for high-density HAMR media.
Article
Nanoscience & Nanotechnology
Claire Donnelly, Aurelio Hierro-Rodriguez, Claas Abert, Katharina Witte, Luka Skoric, Dedalo Sanz-Hernandez, Simone Finizio, Fanfan Meng, Stephen McVitie, Jorg Raabe, Dieter Suess, Russell Cowburn, Amalio Fernandez-Pacheco
Summary: The design of complex magnetic systems through nonlinear interactions or three-dimensional geometries can achieve new functionalities by controlling intrastructure properties and magnetostatic coupling of neighboring magnetic structures. This can lead to new physics and functionalities, such as three-dimensional chiral spin states and spin textures with new spin topologies.
NATURE NANOTECHNOLOGY
(2022)
Article
Multidisciplinary Sciences
Gregor Wautischer, Claas Abert, Florian Bruckner, Florian Slanovc, Dieter Suess
Summary: This paper presents a method for optimizing the topology of hard and soft magnetic structures using the density approach for topology optimization. The stray field is calculated using a hybrid finite element-boundary element method, and the necessary gradients for optimization are efficiently calculated using the adjoint approach. The method's capabilities are showcased by optimizing the topology of hard and soft magnetic thin film structures and the results are verified by comparison with an analytical solution.
SCIENTIFIC REPORTS
(2022)
Article
Chemistry, Multidisciplinary
Luka Skoric, Claire Donnelly, Aurelio Hierro-Rodriguez, Miguel A. Cascales Sandoval, Sandra Ruiz-Gomez, Michael Foerster, Miguel A. Nino, Rachid Belkhou, Claas Abert, Dieter Suess, Amalio Fernandez-Pacheco
Summary: This study proposes a three-dimensional magnetic interconnector that utilizes geometry-driven automotion of domain walls for magnetic information transfer between functional magnetic planes. Through experiments and simulations, it is found that large thickness gradients in the structure are the main mechanism for the automotion of domain walls. This work demonstrates a possible mechanism for efficient transfer of magnetic information in three dimensions.
Article
Materials Science, Multidisciplinary
F. Slanovc, M. Ortner, M. Moridi, C. Abert, D. Suess
Summary: This paper presents an analytical solution for the magnetic field of a homogeneously magnetized cylinder tile and extends it to solutions for full cylinders, rings, cylinder sectors, and ring segments. The solution is derived by direct integration in the magnetic surface charge picture, resulting in closed-form expressions and elliptic integrals. All special cases are treated individually, allowing the computation of the magnetic field for all possible position arguments r ∈ R-3. A Python implementation and performance analysis are provided, and the implementation is tested against numerical solutions and applied to compute the magnetic field in a discrete Halbach cylinder and a rotation sensor system.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Materials Science, Multidisciplinary
Paul Heistracher, Claas Abert, Florian Bruckner, Thomas Schrefl, Dieter Suess
Summary: In this paper, we propose a novel micromagnetic standard problem for calculating the coercive field required to unpin a domain wall at the interface of a multiphase magnet. This problem is sensitive to discontinuities in material parameters such as the exchange interaction, uniaxial anisotropy, and spontaneous magnetization. We derive an explicit treatment of the jump conditions at material interfaces for the exchange interaction in the finite-difference discretization. The micromagnetic simulation results are compared with analytical solutions, showing good agreement. The proposed standard problem is suitable for testing the implementation of both finite-difference and finite-element simulation codes.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Multidisciplinary Sciences
M. Suppan, C. Huber, K. Mathauer, C. Abert, F. Brucker, J. Gonzalez-Gutierrez, S. Schuschnigg, M. Groenefeld, I Teliban, S. Kobe, B. Saje, D. Suess
Summary: In this work, the in-situ alignment of single-crystal magnetic particles inside a polymer matrix using fused filament fabrication is demonstrated. The strontium hexaferrite particles can be well aligned, while the samarium iron nitride particles cannot.
SCIENTIFIC REPORTS
(2022)
Article
Physics, Applied
Zachary R. Nunn, Juliana Besler, Pavlo Omelchenko, Sabri Koraltan, Claas Abert, Dieter Suess, Erol Girt
Summary: We demonstrate that a noncollinear alignment between magnetizations of adjacent ferromagnetic layers can be achieved by coupling two ferromagnetic layers across a magnetic spacer layer consisting of a nonmagnetic material, Ru, alloyed with a ferromagnetic element, Co. The relative angle between the magnetizations of the ferromagnetic layers can be controlled by changing the composition and thickness of the spacer layer between 0 degrees and 180 degrees.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Materials Science, Multidisciplinary
D. Suess, S. Koraltan, F. Slanovc, F. Bruckner, C. Abert
Summary: Within this paper, we demonstrate the significance of accurate implementations of RKKY interactions for antiferromagnetically coupled ferromagnetic layers with thicknesses larger than the exchange length. We develop a benchmark problem to evaluate different implementations of RKKY interaction by deriving an analytical formula for the saturation field of two infinitely thick antiparallelly coupled magnetic layers. Our benchmark problem reveals that current implementations in commonly used finite-difference codes lead to errors in the saturation field, exceeding 20% for mesh sizes of 2 nm, which is below the material's exchange length. To enhance accuracy, we introduce higher order cell-based and nodal-based finite-difference codes that significantly reduce errors compared to existing implementations. With a mesh size of 2 nm, the second-order cell-based approach and the first-order nodal-based approach reduce the error in the saturation field by a factor of 10 (2% error).
Article
Materials Science, Multidisciplinary
Santiago Helbig, Claas Abert, Pedro A. Sanchez, Sofia S. Kantorovich, Dieter Suess
Summary: We propose a simple simulation model to study magnetic and frictional losses of magnetic nanoparticles in viscous fluids under alternating magnetic fields. The model is based on a macrospin approach and solves the Landau-Lifshitz-Gilbert equation coupled with the mechanical torque equation. Despite its simplicity, the model reveals rich physics and allows for a detailed analysis of different loss processes depending on field parameters and initial particle-field arrangement. The model demonstrates the emergence of different steady states depending on these parameters, with regions dominated by magnetic relaxation and high losses or high frictional losses at low fields or frequencies. The energy continuously increases even across regime boundaries, surpassing the viscous relaxation limit. At higher frequencies, the steady state can also depend on the initial particle orientation in the external field. We compare and discuss the general behavior and specific absorption rates for different cases.
Article
Materials Science, Multidisciplinary
A. Troster, J. Pils, F. Bruckner, W. Schranz, I. Rychetsky, C. Verdi
Summary: This study investigates the emergence of polarity in so-called hard antiphase boundaries in strontium titanate using atomistic simulations and numerical solutions. Traditional numerical solutions fail to reproduce the shape and pressure behavior of the domain wall polarization, but adding rotopolar couplings and considering nuclear quantum fluctuations can restore semiquantitative agreement.
Article
Materials Science, Multidisciplinary
Sabri Koraltan, Claas Abert, Florian Bruckner, Michael Heigl, Manfred Albrecht, Dieter Suess
Summary: In this study, we demonstrate the controlled generation and annihilation of (anti)skyrmions with tunable chirality in magnetic heterostructures through micromagnetic simulations. The stability of the (anti)skyrmion depends on the polarization of the (anti)vortex, while their chirality is determined by the (anti)vortices. We also predict that the same coupling mechanism works for chiral skyrmions by introducing the interlayer Dzyaloshinskii-Moriya interaction. Furthermore, we show that the core coupling between the (anti)vortices and (anti)skyrmions allows controlled deletion and writing of spin objects.