arXiv subjects

Oliver Gutfleisch

Publications and source records attributed to Oliver Gutfleisch.

At least 19 recordsLinked to original sources

arXiv2026

Muscle-inspired magnetic actuators that push, pull, crawl, and grasp

Functional magnetic composites capable of large deformation, load bearing, and multifunctional motion are essential for next-generation adaptive soft robots. Here, we present muscle-inspired magnetic actuators (MMA), additively manufactured from a thermoplastic/permanent magnet polyurethane/Nd2Fe14B (TPU/MQP-S) composite using laser powder bed fusion (LPBF). By tuning the laser-energy scale between 1.0 and 3.0, both mechanical stiffness and magnetic response are precisely controlled: the tensile strength increases from 0.28 to 0.99 MPa while maintaining 30-45% elongation at break. This process enables the creation of 0.5 mm-thick flexural hinges, which reversibly bend and fold under moderate magnetic fields without damage. Two actuator types are reported showing the system versatility. The elongated actuator with self-weight of 1.57 g, magnetized in its contracted state, achieves linear contraction under a 500 mT field, lifting 50 g (32x its own weight) and sustaining performance over at least 50 cycles. Equipped with anisotropic frictional feet, it supports movement of a magnetic crawling robot that achieves up to 100% locomotion success on textured substrates. The expandable actuator exhibits reversible opening and closing under a 300 mT field, reliably grasping and releasing different objects, including soft berries and rigid 3D printed geometries. It can also anchor in a tube while holding suspended 50 g loads. This work demonstrates a LPBF-based strategy to program both stiffness and magnetization within a single material system, enabling remotely driven, reconfigurable, and fatigue-resistant soft actuators. The approach opens new possibilities for force controlled, multifunctional magnetic soft robots for adaptive gripping, locomotion, and minimally invasive manipulation of biomedical tools.

cs.RO↗

arXiv2026

Influence of Ni substitution on the phase transitions and magnetocaloric effect of NdCo2 at cryogenic temperatures

We have investigated NdCo2-xNix cubic Laves compounds with 0 <= x <= 1 using neutron diffraction and bulk magnetization measurements to study the influence of partial Ni substitutions of Co on the phase transitions and the magnetocaloric effect. Upon cooling, NdCo2 undergoes a cubic to tetragonal transition at 100 K, and a tetragonal to orthorhombic transition at 42 K. The transitions are associated with long-range ferromagnetic ordering of the magnetic moments along the c axis and spin reorientation into the ab plane, respectively. Both transitions shift to lower temperatures as the Ni content x increases. For x >= 0.5, the orthorhombic phase is suppressed. Additionally, there was a reduction in the magnetic moment upon increasing the Ni substitution of Co. The magnetocaloric effect was determined both indirectly and directly, with good agreement between the methods. NdCo2 exhibits an adiabatic temperature change of 6.3 K for a field of 20 T, which is decreased to 4.9 K for NdCoNi for the same field strength due to the reduced magnetic moment upon Ni substitution.

cond-mat.mtrl-sci↗

arXiv2026

Defect Detection in Magnetic Systems Using U-Net and Statistical Measures

Local material inhomogeneities can strongly influence magnetization dynamics and macroscopic magnetic properties, yet detecting such defects from magnetic imaging data remains challenging when thermal fluctuations and experimental noise obscure static contrast. Here, we investigate defect detection in strongly fluctuating magnetization regimes where signatures of inhomogeneities largely average out in time-resolved measurements. Using finite-temperature micromagnetic simulations with randomly distributed defects and material parameters representative of \ce{Ni80Fe20}, we compute per-pixel temporal mean, temporal standard deviation, and latent entropy and use them as inputs for U-Net-based semantic segmentation models. We find that the most effective descriptor depends on the noise level and, importantly, that robust detection requires training data that reflect the expected noise statistics. These results provide practical guidance for designing noise-robust defect-detection workflows in magnetic imaging.

cond-mat.mtrl-sci↗

arXiv2025

A voltage-responsive strongly dipolar-coupled macrospin network with emergent dynamics for computing

Emergent behavior, which arises from local interactions between simple elements, is pervasive in nature. It underlies the energy-efficient computing in our brains. However, realizing such dynamics in artificial materials, particularly under low-energy stimuli, remains a fundamental challenge. While dipole-dipole interactions are typically suppressed in magnetic storage, here we harness and amplify them to construct a strongly dipolar-coupled network of SmCo5 macrospins at wafer scale, which can exhibit intrinsic interaction-driven collective dynamics in response to voltage pulses. The network combines three essential ingredients: strong dipolar coupling by large single-domain macrospin, giant voltage control of coercivity over nearly 1000-fold, and disordered network topology with frustrated Ising-like energy landscape. When stimulated by 1 V pulses, the network enters a regime where interaction-driven magnetic behaviors emerge, including spontaneous demagnetization, greatly enhanced magnetization modulation, reversible freeze and resume evolution and stochastic convergence toward low-energy magnetic configurations. All these behaviors are completely absent at the single-nanomagnet level. Furthermore, by constructing micromagnetic models of the strongly dipolar-coupled macrospin networks, we show that the resulting nonlinear, high-dimensional collective dynamics, intrinsic to strongly-interacting systems, can enable accurate chaotic Mackey-Glass prediction and multiclass drone-signal classification. Our work establishes the voltage-responsive strongly-coupled SmCo5 network as a mesoscopic platform for probing emergent magnetic dynamics previously inaccessible under ambient conditions. It also suggests a fundamental distinct route towards scalable, low-voltage computing, one rooted in native physical interaction-driven collective dynamics at the network level.

cond-mat.mtrl-sci↗

arXiv2025

New insights into the magnetism of DyCo$_{5}$

In this work, we present the first magnetization measurements of DyCo$_5$ single crystals in magnetic fields up to 14 T, spanning a temperature range up to 600 K. Our investigation reveals several unique features, including a significant magnetization anisotropy and an observed minimum in spontaneous magnetization near the compensation point, phenomena not previously reported. This work also uncovers the complex magnetic behavior of DyCo$_5$, with a pronounced interplay between the Dy and Co sublattices, each exhibiting distinct temperature-dependent magnetic properties. The combination of dynamical mean-field theory (DMFT), atomistic spin-dynamics (ASD) simulations, and the Effective Spin Model (ESM) for rare-earth compounds successfully explains the experimental data across both low and high temperatures. Our theoretical approach not only explains the observed magnetic anisotropy and the behavior near the compensation temperature but also successfully reproduces key experimental features such as the saturation behavior at high fields and the evolution of the magnetic moment at different temperatures.

cond-mat.mtrl-sci↗

arXiv2025

Ultralow-Cost magnetocaloric compound for Cryogenic Cooling

Cost-effective materials are essential for large-scale deployment. The emerging magnetocaloric hydrogen liquefaction technology could transform the liquid hydrogen industry due to its potential in achieving higher efficiency. Most studies of the cryogenic magnetocaloric effect (MCE) have focused on resource-critical rare-earth-based compounds. Here we report on an ionic magnetocaloric compound FeCl$_2$ which is based on ultralow-cost elements, as a candidate working material for hydrogen liquefaction. FeCl$_2$ shows both inverse and conventional MCE. From 0 to 1.5 T, the inverse effect yields a positive magnetic entropy change ($\Delta S_T$) of about 5 J/kg/K near 20 K, then declines toward zero at higher fields. In contrast, the conventional (negative) response strengthens with field. The $\Delta S_T$ reaches 18.6 J/kg/K near 20 K in magnetic fields of 5 T. This value exceeds most light rare-earth-based compounds and approaches that of heavy rare-earth-based compounds. In magnetic fields of 5 T, the adiabatic temperature change reaches about 3.6 K. The large $\Delta S_T$, along with the low cost of the elements in FeCl$_2$, are prerequisites for inexpensive industrial-scale production, giving the prospect of a practical magnetocaloric candidate for hydrogen liquefaction in the 20 $\sim$ 77 K temperature window.

cond-mat.mtrl-sci↗

arXiv2025

Direct observation of nanoscale pinning centers in Ce(Co0.8Cu0.2)5.4 permanent magnets

Permanent magnets containing rare earth elements are essential components for the electrification of society. Ce(Co1-xCux)5 permanent magnets are a model system known for their substantial coercivity, yet the underlying mechanism remains unclear. Here, we investigate Ce(Co0.8Cu0.2)5.4 magnets with a coercivity of ~1 T. Using transmission electron microscopy (TEM) and atom probe tomography (APT), we identify a nanoscale cellular structure formed by spinodal decomposition. Cu-poor cylindrical cells (~5-10 nm in diameter, ~20 nm long) have a disordered CeCo5-type structure and a composition Ce(Co0.9Cu0.1)5.3. Cu-rich cell boundaries are ~ 5 nm thick and exhibit a modified CeCo5 structure, with Cu ordered on the Co sites and a composition Ce(Co0.7Cu0.3)5.0. Micromagnetic simulations demonstrate that the intrinsic Cu concentration gradients up to 12 at.% Cu/nm lead to a spatial variation in magnetocrystalline anisotropy and domain wall energy, resulting in effective pinning and high coercivity. Compared to Sm2Co17-type magnets, Ce(Co0.8Cu0.2)5.4 displays a finer-scale variation of conventional pinning with lower structural and chemical contrast in its underlying nanostructure. The identification of nanoscale chemical segregation in nearly single-phase Ce(Co0.8Cu0.2)5.4 magnets provides a microstructural basis for the long-standing phenomenon of "giant intrinsic magnetic hardness" in systems such as SmCo5-xMx, highlighting avenues for designing rare-earth-lean permanent magnets via controlled nanoscale segregation.

cond-mat.mtrl-sci↗

arXiv2025

Control of Covalent Bond Enables Efficient Magnetic Cooling

Magnetic cooling, harnessing the temperature change in matter when exposed to a magnetic field, presents an energy-efficient and climate-friendly alternative to traditional vapor-compression refrigeration systems, with a significantly lower global warming potential. The advancement of this technology would be accelerated if irreversible losses arising from hysteresis in magnetocaloric materials were minimized. Despite extensive efforts to manipulate crystal lattice constants at the unit-cell level, mitigating hysteresis often compromises cooling performance. Herein, we address this persistent challenge by forming Sn(Ge)3/Sn(Ge)3 bonds within the unit cell of the Gd5Ge4 compound. Our approach enables an energetically favorable phase transition, leading to the elimination of thermal hysteresis. Consequently, we achieve a synergistic improvement of two key magnetocaloric figures of merit: a larger magnetic entropy change and a twofold increase in the reversible adiabatic temperature change (from 3.8 to 8 K) in the Gd5Sn2Ge2 compound. Such synergies can be extended over a wide temperature range. This study demonstrates a paradigm shift in mastering hysteresis toward simultaneously achieving exceptional magnetocaloric metrics and opens up promising avenues for gas liquefaction applications in the longstanding pursuit of sustainable energy solutions.

cond-mat.mtrl-sci↗

arXiv2025

An Open-Source User-Friendly Interface for Simulating Magnetic Soft Robots using Simulation Open Framework Architecture (SOFA)

Soft robots, particularly magnetic soft robots, require specialized simulation tools to accurately model their deformation under external magnetic fields. However, existing platforms often lack dedicated support for magnetic materials, making them difficult to use for researchers at different expertise levels. This work introduces an open-source, user-friendly simulation interface using the Simulation Open Framework Architecture (SOFA), specifically designed to model magnetic soft robots. The tool enables users to define material properties, apply magnetic fields, and observe resulting deformations in real time. By integrating intuitive controls and stress analysis capabilities, it aims to bridge the gap between theoretical modeling and practical design. Four benchmark models -- a beam, three- and four-finger grippers, and a butterfly -- demonstrate its functionality. The software's ease of use makes it accessible to both beginners and advanced researchers. Future improvements will refine accuracy through experimental validation and comparison with industry-standard finite element solvers, ensuring realistic and predictive simulations of magnetic soft robots.

cs.RO↗

arXiv2025

Optimizing $\alpha''$-Fe$_{16}$N$_2$ as permanent magnet via alloying

Based on systematic first-principles calculations, we investigate the effects of 27 alloying elements on the intrinsic magnetic properties of Fe$_{16}$N$_2$, in order to further optimize its properties for permanent magnet applications. Analysis on the thermodynamic stabilities based on formation energy and distance to the convex hull reveals that 20 elements can be substituted into Fe$_{16}$N$_2$, where there is no strong site-preference upon doping. It is observed that all alloying elements can essentially reduce the saturation magnetization, whereas the magnetic anisotropy can be significantly modified. In terms of the Boltzmann-average intrinsic properties, we identify 8 elements as interesting candidates, with Co, Mo, and W as the most promising cases for further experimental validations.

cond-mat.mtrl-sci↗

arXiv2025

Effect of Ag nano-additivation on microstructure formation in Nd-Fe-B magnets built by laser powder bed fusion

Laser powder bed fusion (PBF-LB/M) enables the near-net shape production of permanent magnets with complex geometry while reducing material waste. However, controlling the microstructure and optimizing magnetic properties remain challenging due to rapid solidification and intrinsic heat treatment effects occurring during both inter-layer and intra-layer processing. Surface additivation of the feedstock powder with Ag nanoparticles (NPs) is a concept that has been shown to increase the coercivity of PBF-LB/M-produced Nd-Fe-B magnets. Using atom probe tomography (APT) and transmission electron microscopy (TEM), we reveal that Ag nano-additivation promotes heterogeneous nucleation of the Nd2Fe14B phase, leading to refined, equiaxed grains and increased stability of the Ti-Zr-B-rich intergranular phase. The intrinsic heat treatment, influenced by layer-wise processing, further affects the distribution of Ag-rich regions, impacting grain growth and intergranular phase composition across different regions of the melt pool. Compared to the unadditivated sample, the Ag-additivated sample exhibits a significantly finer grain structure and a changed intergranular phase, which contribute to enhanced domain wall pinning and coercivity. These microstructural changes directly modify the magnetic domain structure, as evidenced by Lorentz transmission electron microscopy (TEM). Our results highlight that the interplay between nano-additivation and in-process heat treatment provides a novel pathway for tailoring the microstructure and enhancing the magnetic performance of permanent magnets.

cond-mat.mtrl-sci↗

arXiv2024

Formation of cellular/lamellar nanostructure in Sm$_2$Co$_{17}$-type binary and ternary Sm-Co-Zr magnets

2:17 SmCo magnets with a quinary composition of Sm(Co,Cu,Fe,Zr)$_{7+{\delta}}$ are industrially relevant hard magnets used in high temperature and corrosive environments. Their complex cellular/lamellar nanostructure, consisting of ordered 2:17 phase cells, 1:5 phase cell boundaries and Z-phase (Zr-rich) lamellae, is essential for their high coercivity. However, the system's complexity makes it challenging to determine the contribution of each element or microstructural feature to coercivity. To disentangle the microstructure-property relationships, we simplified the system to binary and ternary SmCo$_{7.7-x}$Zr$_x$ (with $x = 0$ and 0.1) magnets and conducted detailed micro- to atomic-scale analyses. Only Zr-containing magnets formed a cellular/lamellar nanostructure akin to industrial magnets, in Zr-rich regions with at least 1 at.% Zr, but without achieving high coercivity due to low elemental gradients in absence of Cu across cell boundaries. Data from Zr-poor areas of SmCo$_{7.6}$Zr$_{0.1}$ suggests that 2:17 phase twin boundaries facilitate cellular nanostructure formation by providing inhomogeneities for heterogeneous nucleation.

cond-mat.mtrl-sci↗

arXiv2024

Understanding High Coercivity in ThMn12-Type Sm-Zr-Fe-Co-Ti Permanent Magnet Powders through Nanoscale Analysis

ThMn12-type (Sm,Zr)1(Fe,Co,Ti)12 compounds show great potential for permanent magnets. Magnetically hard anisotropic powders prepared via reduction-diffusion exhibit a significant increase in coercivity from 0.45 T to 1.26 T as the processing temperature is raised from 990{\deg}C to 1220{\deg}C. Structural and microchemical analyses at high-resolution reveal that high-temperature processing annihilates grain boundaries (GBs) and reduces the density of twin boundaries (TBs), which are defects acting as weak links limiting the coercivity in the 1:12 system. Ostwald ripening is proposed as the mechanism behind the reduction of GB and TB densities at higher temperature, driven by the reduction in interfacial energy and enhancing atomic structural uniformity.

cond-mat.mtrl-sci↗

arXiv2024

Design of thermal hysteresis in nonstoichiometric alloys with giant magnetocaloric effect

The non-stoichiometric Fe$_2$P-type (FeMnP$_{0.5}$Si$_{0.5}$)$_{1-x}$(FeV)$_{x}$ alloys ( $x=0, 0.01$, $0.02$, and $0.03$) have been investigated as potential candidates for magnetic refrigeration near room temperature. The magnetic ordering temperature decreases with increasing FeV concentration, $x$, which can be ascribed to decreased ferromagnetic coupling strength between the magnetic atoms. The strong magnetoelastic coupling in these alloys results in large values of the isothermal entropy change ($\Delta S_M$); $15.7$ J/kgK, at $2$ T magnetic field for the $x = 0$ alloy. $\Delta S_M$ decreases with increasing $x$. Results from M{\"o}ssbauer spectroscopy reveal that the average hyperfine field (in the ferromagnetic state) and average center shift (in the paramagnetic state) have the same decreasing trend as $\Delta S_M$. The thermal hysteresis ($\Delta T_{hyst}$) of the magnetic phase transition decreases with increasing $x$, while the mechanical stability of the alloys improves due to the reduced lattice volume change across the magnetoelastic phase transition. The adiabatic temperature change $\Delta T_{ad}$, which highly depends on $\Delta T_{hyst}$, is $1.7$ K at $1.9$ T applied field for the $x = 0.02$ alloy.

cond-mat.mtrl-sci↗

arXiv2024

Coercivity influence of nanostructure in SmCo-1:7 magnets: Machine learning of high-throughput micromagnetic data

As a pinning-controlled permanent magnet, tailoring the cellular nanostructure of samarium-cobalt-based 1:7-type (SmCo-1:7) magnets remains crucial for improving magnetic performance. Jointing forward and inverse machine learning models with the high-throughput micromagnetic simulations (42,300 runs), we identify the nanostructural and magnetic features that are most effective for coercivity, combining both nucleation and pinning mechanisms. Sensitivity analyses reveal that the 1:5-phase enhances coercivity by providing high anisotropy, and the Z-phase strengthens pinning through fluctuations in domain wall energy. Cu additions in the 1:5-phase significantly reduce coercivity, while Fe substitutions in the 2:17-phase modestly reduce coercivity but improve pinning locally and increase saturation magnetization. Among all examined features, magnetocrystalline misorientation emerges as the dominant factor. Finally, the framework enables the inverse design of nanostructures with prescribed coercivity, demonstrating a computationally cost-effective toolkit for guiding the performance tailoring of SmCo-1:7 magnets.

cond-mat.mtrl-sci↗

arXiv2024

The role of Debye temperature in achieving large adiabatic temperature changes at cryogenic temperatures: a case study on $Pr_2In$

The excellent magnetic entropy change ($ΔS_T$) in the temperature range of 20 $\sim$ 77 K due to the first-order phase transition makes $Pr_2In$ an intriguing candidate for magnetocaloric hydrogen liquefaction. As an equally important magnetocaloric parameter, the adiabatic temperature change ($ΔT_{ad}$) of $Pr_2In$ associated with the first-order phase transition has not yet been reported. In this work, the $ΔT_{ad}$ of $Pr_2In$ is obtained from heat capacity measurements: 2 K in fields of 2 T and 4.3 K in fields of 5 T. While demonstrating a $ΔT_{ad}$ that is not as impressive as its remarkable $ΔS_T$, $Pr_2In$ exhibits an unusual low Debye temperature ($T_D$) of around 110 K. Based on these two observations, an approach that combines the mean-field and Debye models is developed to study the correlation between $ΔT_{ad}$ and $T_D$. The role of $T_D$ in achieving large $ΔT_{ad}$ is revealed: materials with higher $T_D$ tend to exhibit larger $ΔT_{ad}$, particularly in the cryogenic temperature range. This discovery explains the absence of an outstanding $ΔT_{ad}$ in $Pr_2In$ and can serve as a tool for designing or searching materials with both a large $ΔS_T$ and a $ΔT_{ad}$.

cond-mat.mtrl-sci↗

arXiv2023

Magneto-active composites with locally tailored stiffness produced by laser powder bed fusion

Additive manufacturing technologies enable the production of complex and bioinspired shapes using magneto-responsive materials, which find diverse applications in soft robotics. Particularly, the development of composites with controlled gradients in mechanical properties offers new prospects for advancements in magneto-active materials. However, achieving such composites with gradients typically involves complex multi-material printing procedures. In this study, a single-step laser powder bed fusion (LPBF) process is proposed that enables precise local adjustments of the mechanical stiffness within magneto-active composites. By utilizing distinct laser parameters in specific regions of a composite containing thermoplastic polyurethane and atomized magnetic powder derived from hard magnetic Nd-Fe-B, the stiffness of the composite can be modified within the range of 2 to 22 MPa. Various magneto-responsive actuators with locally tailored stiffness are fabricated and their magnetic performance is investigated. The enhanced response exhibited by actuators with locally adjusted mechanical properties in comparison to their homogeneous counterparts with identical geometries is shown. As a demonstration of a biomedical application, a magnetically responsive stent with localized adjustment is presented with the ability to meet specific requirements in terms of geometry and local stiffness based on an individual's anatomy and disease condition. The proposed method presents an approach for creating functionally graded materials using LPBF, not only for magneto-active materials but also for several other structural and functional materials.

physics.app-ph↗

arXiv2023

Voltage-driven 90 switching of bulk perpendicular magnetic anisotropy in ferrimagnets

Unravelling the mechanism behind bulk perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal films has proven challenging. This is largely due to the inherent complexity of amorphous structure and the entangled potential origins arising from microstructure and atomic structure factors. Here, we present an approach wherein the magneto-electric effect is harnessed to induce 90{\deg} switching of bulk PMA in Tb-Co films to in-plane directions by applying voltages of only -1.2 V. This manipulation is achieved by voltage-driven insertion of hydrogen atoms into interstitial sites between Tb and Co atoms, which serves as a perturbation to local atomic structure. Using angle-dependent X-ray magnetic circular dichroism, we find that the anisotropy switching originates from the distortion of crystal field around Tb which reorients the alignment of Tb orbital moments. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90{\deg}, as substantiated by ab-initio calculations. Our study not only concludes the atomic origin of Tb-Co atom bonding configuration in shaping bulk PMA, but also establishes the groundwork for electrically programmable ferrimagnetic spintronics, such as controlling domain wall motion and programming artificial spin textures.

cond-mat.mtrl-sci↗