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Anomalous low-field magnetoresistance in Fe$_3$Ga$_4$ single crystals
Authors:
Michelle E. Jamer,
Gregory M. Stephen,
Brandon Wilfong,
Radhika Barua,
Frank M. Abel,
Steven P. Bennett,
Joseph C. Prestigiacomo,
Don Heiman,
Dave Graf
Abstract:
Fe$_3$Ga$_4$ possesses a helical spin spiral with a complex competition between ferromagnetic and antiferromagnetic ground states. This competition generates multiple metamagnetic transitions that are governed by both applied magnetic field and temperature. At intermediate temperatures between T$_1$ (68 K) and T$_2$ (360 K), the ferromagnetically aligned spins transition to an antiferromagnetic sp…
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Fe$_3$Ga$_4$ possesses a helical spin spiral with a complex competition between ferromagnetic and antiferromagnetic ground states. This competition generates multiple metamagnetic transitions that are governed by both applied magnetic field and temperature. At intermediate temperatures between T$_1$ (68 K) and T$_2$ (360 K), the ferromagnetically aligned spins transition to an antiferromagnetic spin spiral. In this study, magnetoresistance (MR) measurements are performed on an aligned single crystal and compared to magnetization properties in order to gain insight on the unique alignment of the spins. The high-field MR is positive at low temperatures indicating cyclotronic behavior and negative at high temperature from electron-magnon scattering. Of particular significance is a large anomalous positive MR at low fields, possibly due to emergent spin fluctuations thus prompting further exploration of this multifaceted material.
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Submitted 30 September, 2025;
originally announced October 2025.
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Interplay between Exchange Interaction and Magnetic Shape Anisotropy of ferromagnetic nanoparticles in a non-magnetic matrix for rare-earth-free permanent magnets
Authors:
Shouvik Sarker,
Md Mahadi Rajib,
Radhika Barua,
Jayasimha Atulasimha
Abstract:
Developing permanent magnets with fewer critical elements requires understanding hysteresis effects and coercivity through visualizing magnetization reversal. Here, we numerically investigate the effect of the geometry of nanoscale ferromagnetic inclusions in a paramagnetic/non-magnetic matrix to understand the key factors that maximize the magnetic energy product of such nanocomposite systems. Sp…
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Developing permanent magnets with fewer critical elements requires understanding hysteresis effects and coercivity through visualizing magnetization reversal. Here, we numerically investigate the effect of the geometry of nanoscale ferromagnetic inclusions in a paramagnetic/non-magnetic matrix to understand the key factors that maximize the magnetic energy product of such nanocomposite systems. Specifically, we have considered a matrix of 3 micron x 3 micron x40 nanometer dimension, which is a sufficiently large volume, two-dimensional representation considering that the ferromagnetic inclusions thickness is less than 3.33% of the lateral dimensions simulated. Using this approach that is representative of bulk behavior while being computationally tractable for simulation, we systematically studied the effect of the thickness of ferromagnetic strips, the separation between the ferromagnetic strips due to the nonmagnetic matrix material, and the length of these ferromagnetic strips on magnetic coercivity and remanence by simulating the hysteresis loop plots for each geometry. Furthermore, we study the underlying micromagnetic mechanism for magnetic reversal to understand the factors that could help attain the maximum magnetic energy densities for ferromagnetic nanocomposite systems in a paramagnetic/non-magnetic material matrix. In this study, we have used material parameters of an exemplary Alnico alloy system, a rare-earth-free, thermally stable nanocomposite, which could potentially replace high-strength NdFeB magnets in applications that don't require large energy products. This can stimulate further experimental work on the fabrication and large-scale manufacturing of RE-free PMs with such nanocomposite systems.
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Submitted 2 August, 2024;
originally announced August 2024.
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Effect of X-Ray Irradiation on Magnetocaloric Material, (MnNiSi)1-x(Fe2Ge)x
Authors:
John Peter J. Nunez,
Vaibhav Sharma,
Jessika V. Rojas,
Radhika Barua,
Ravi L. Hadimani
Abstract:
(MnNiSi)1-(Fe2Ge)x composition (x=0.34) alloy was prepared by arc melting, crushed, and sieved to approximately <32 microns. They were utilized in examining the possible magnetic and structural changes when exposed to a dosage of a continuous sweeping rate of ~>120 Gy/min and an absorbed dose of 35 kGy of X-ray radiation. This study reports observable trends in X-ray diffraction and magnetic measu…
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(MnNiSi)1-(Fe2Ge)x composition (x=0.34) alloy was prepared by arc melting, crushed, and sieved to approximately <32 microns. They were utilized in examining the possible magnetic and structural changes when exposed to a dosage of a continuous sweeping rate of ~>120 Gy/min and an absorbed dose of 35 kGy of X-ray radiation. This study reports observable trends in X-ray diffraction and magnetic measurements. Magnetization in the magnetization vs. temperature (both heating and cooling) measurements showed an increase from 2.72 emu/g to 4.01 emu/g in the irradiated sample. The Magnetization vs. magnetic field loops exhibited irradiation-induced magnetic hysteresis. The irradiated sample also exhibited an observable change in its coercivity of ΔHc = 14.7% at 200 K. A maximum entropy change ΔSmag of ~ 11.139 J/kg*K and a Tave peak of 317.5 K was achieved for the pristine sample in comparison to ΔSmag of ~ 11.349 J/kg*K and a Tave peak of 312.5 K for the irradiated sample. These presented results provided deeper insights into tuning the effect of irradiation to the magnetic properties of (MnNiSi)1-(Fe2Ge)x for composition (x=0.34) that can be utilized in a wide range of magnetocaloric applications in high-energy radiation environments. The irradiation applied to the sample did not induce any structural or magnetic phase changes in the selected composition but modified the magnetic properties marginally.
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Submitted 15 March, 2023;
originally announced March 2023.
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The effect of vanadium substitution on the structural and magnetic properties of (Fe$_{1-x}$V$_{x}$)$_{3}$Ga$_{4}$
Authors:
Brandon Wilfong,
Vaibhav Sharma,
Omar Bishop,
Adrian Fedorko,
Don Heiman,
Radhika Barua,
Michelle E. Jamer
Abstract:
Fe$_{3}$Ga$_{4}$ displays a complex magnetic phase diagram that is sensitive and tunable with both electronic and crystallographic structure changes. In order to explore this tunability, vanadium-doped (Fe$_{1-x}$V$_{x}$)$_{3}$Ga$_{4}$ has been synthesized and characterized. High-resolution synchrotron X-ray diffraction and Rietveld refinement show that samples up to 20\% V-doping remain isostruct…
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Fe$_{3}$Ga$_{4}$ displays a complex magnetic phase diagram that is sensitive and tunable with both electronic and crystallographic structure changes. In order to explore this tunability, vanadium-doped (Fe$_{1-x}$V$_{x}$)$_{3}$Ga$_{4}$ has been synthesized and characterized. High-resolution synchrotron X-ray diffraction and Rietveld refinement show that samples up to 20\% V-doping remain isostructural to Fe$_{3}$Ga$_{4}$ and display a linear increase in unit cell volume as doping is increased. Magnetic measurements reveal a suppression of the antiferromagnetic helical spin-density wave (SDW) with V-doping, revealed by changes in both the low-temperature ferromagnetic-antiferromagentic (FM-AFM) transition (T$_{1}$) and high-temperature AFM-FM transition (T$_{2}$). At 7.5\% V-doping, the metamagnetic behavior of the helical AFM SDW phase is no longer observed. These results offer an avenue to effective tuning of the magnetic order in Fe$_{3}$Ga$_{4}$ for devices, as well as increased understanding of the magnetism in this system.
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Submitted 3 October, 2022;
originally announced October 2022.
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Altering the magnetic ordering of Fe$_{3}$Ga$_{4}$ via thermal annealing and hydrostatic pressure
Authors:
Brandon Wilfong,
Vaibhav Sharma,
Jared Naphy,
Omar Bishop,
Steven P. Bennett,
Joseph Prestigiacomo,
Radhika Barua,
Michelle E. Jamer
Abstract:
The effects of post-synthesis annealing temperature on arc-melted samples of Fe$_{3}$Ga$_{4}$ has been studied to investigate changes in crystallographic and magnetic properties induced by annealing. Results show a significant trend in the evolution of the (incommensurate spin density wave) ISDW-FM (ferromagnetic) transition temperature as a function of the refined unit cell volume in annealed sam…
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The effects of post-synthesis annealing temperature on arc-melted samples of Fe$_{3}$Ga$_{4}$ has been studied to investigate changes in crystallographic and magnetic properties induced by annealing. Results show a significant trend in the evolution of the (incommensurate spin density wave) ISDW-FM (ferromagnetic) transition temperature as a function of the refined unit cell volume in annealed samples. Strikingly, this trend allowed for the tuning of the transition temperature down to room-temperature (300 K) whilst maintaining a sharp transition in temperature, opening the door to the use of Fe$_{3}$Ga$_{4}$ in functional devices. Crystallographic analysis through Rietveld refinement of high-resolution x-ray diffraction data has showed that arc-melted stoichiometric Fe$_{3}$Ga$_{4}$ is multi-phase regardless of annealing temperature with a minor phase of FeGa$_{3}$ decreasing in phase fraction at higher annealing temperature. In order to validate the trend in ISDW-FM transition temperature with regard to unit cell volume, high pressure magnetometry was performed. This showed that the FM-ISDW ($\sim$ 68 K) and ISDW-FM ($\sim$ 360 K) transition temperatures could be tuned, increased and decreased respectively, linearly with external pressure. Thus, external pressure and the ensuing crystallographic changes minimize the temperature range of the stability of the ISDW pointing toward the importance of structural properties on the mechanism for the formation of the intermediate ISDW phase. These results show how this model system can be tuned as well as highlighting the need for future high-pressure crystallography and related single crystal measurements to understand the mechanism and nature of the intermediate ISDW phase to be exploited in future devices.
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Submitted 20 October, 2021;
originally announced October 2021.
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Universal Properties of Linear Magnetoresistance in Strongly Disordered Semiconductors
Authors:
H. G. Johnson,
S. P. Bennett,
R. Barua,
L. H Lewis,
D. Heiman
Abstract:
Linear magnetoresistance occurs in semiconductors as a consequence of strong electrical disorder and is characterized by nonsaturating magnetoresistance that is proportional to the applied magnetic field. By investigating a disordered MnAs-GaAs composite material, it is found that the magnitude of the linear magnetoresistance (LMR) is numerically equal to the carrier mobility over a wide range and…
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Linear magnetoresistance occurs in semiconductors as a consequence of strong electrical disorder and is characterized by nonsaturating magnetoresistance that is proportional to the applied magnetic field. By investigating a disordered MnAs-GaAs composite material, it is found that the magnitude of the linear magnetoresistance (LMR) is numerically equal to the carrier mobility over a wide range and is independent of carrier density. This behavior is complementary to the Hall effect that is independent of the mobility and dependent on the carrier density. Moreover, the LMR appears to be insensitive to the details of the disorder and points to a universal explanation of classical LMR that can be applied to other material systems.
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Submitted 9 July, 2010;
originally announced July 2010.