Contracting non-Joulian magnets

Saurav, Tanvir M.; Forst, Marcus L.; Boligitz, James A.; Chopra, Harsh Deep

doi:10.1103/physrevb.95.174425

Cited by 6 publications

(19 citation statements)

References 20 publications

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“…The authors believe the non-volume conserving property depends on long range periodicity which they only observed in quenched samples. The same non-volume conserving behavior was observed in Fe-Ge and Fe-Al alloys [55].…”

Section: Domain Structures In Galfenolsupporting

confidence: 75%

Magnetic Domain Structures in Fe-Ga Alloys

Tianen¹

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Section: Domain Structures In Galfenolsupporting

confidence: 75%

Magnetic Domain Structures in Fe-Ga Alloys

Tianen¹

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“…Through accurate placement of gauges, the observed large non‐equivalence of magnetostriction strain for equivalent crystal axes is unambiguously ascertained. The nominal accuracy in aligning a strain gauge along a given axis is ≈1°, which may not fully convey the precision and accuracy of actual experiments, as demonstrated in the recent characterization of non‐Joulian Fe‐Si crystals, to an accuracy of ≈0.1 ppm between equivalent axes …”

Section: Methodsmentioning

confidence: 99%

“…The nominal accuracy in aligning a strain gauge along a given axis is %1 , which may not fully convey the precision and accuracy of actual experiments, as demonstrated in the recent characterization of non-Joulian Fe-Si crystals, to an accuracy of %0.1 ppm between equivalent axes. [11] The high-resolution magnetostriction measurements do not imply probing a small region of the crystal. The measurements described here use large gauge-length strain gauges to ensure maximal coverage of the flat disc surface, and it is these "bulk" measurements that are at the aforesaid resolution.…”

Section: Methodsmentioning

confidence: 99%

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Non‐Joulian Magnetostriction and Non‐Joulian Magnetism

Chopra

Ravishankar

Pacifico

et al. 2018

Physica Status Solidi (b)

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Complementing volume‐conserving Joule magnetostriction (JM), the non‐Joulian magnetostriction (NJM) phenomenon has recently been discovered whose hallmark is change in volume of the crystals in magnetic fields. This article reviews the unique set of non‐Joulian properties that are so non‐conforming relative to conventional magnets that they merit the designation of a distinctly new class of (functional) magnets. This review distils key aspects of non‐Joulian magneto‐elasticity and magnetism, including the sign of volume change (contracting or expanding); the orientation dependence of volume change that is key to realizing large volume changes (remarkably, this volume‐anisotropy coexists with a seemingly isotropic magnetization response for all crystal axes); and a digital coercivity landscape unlike that seen in conventional magnets. NJM lay undiscovered for nearly two decades because prior literature assumed, without experimental foundation, that iron‐based alloys obeyed volume‐conserving JM. Measurements now show that volume change is inherent across wide composition ranges, occurring in both quenched, metastable, and inexorably slow‐cooled, equilibrated crystals. While not essential, quenching promotes long‐range periodicity of magneto‐elastic gradients with enhanced NJM. Another objective is to “frame” Joulian‐to‐non‐Joulian behavior within a single framework of magnetically responsive, wave‐like elastic medium in which approach to homogeneity yields the limiting case of JM; in fact, gradient magnet‐elasticity is indispensable to describing non‐Joulian magnetism. A consequential auxiliary finding is the large differences in intrinsic magneto‐elastic constants for seemingly equivalent crystal axes, consistent with gradient magneto‐elasticity. Consequentially, a sizeable literature that previously characterized these crystals using volume‐conserving assumption and framework of phenomenological magnetostriction theory of homogeneous cubic crystals is rendered moot, and unreliable for high‐fidelity applications.

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“…25,26) Whereas it has been observed that a volume expands in the magnetostriction of the FeGa alloys, volume-contracting NJM has been reported in Fe19.2 at%Ge and Fe33 at%Al alloys. 27) A schematic of the distortion in magnetostriction in these alloys under a field applied along the [010] direction is illustrated in Fig. 3(b); herein, the total volume change by the magnetic field is negative.…”

Section: Magnetostriction Of Bcc Iron-based Alloysmentioning

confidence: 99%

Anisotropy of Magnetostriction of Functional BCC Iron-Based Alloys

et al. 2019

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This paper provides an overview of recent studies on the anisotropy of magnetostriction of functional iron-based alloys with the bodycentered cubic (bcc) structure; these are potential ferromagnetic materials for use in actuators and sensors at ambient temperature. The magnetostrictive properties of these functional iron-based alloys (such as FeGa, FeAl, and FeGe alloys) are known to strongly depend on the crystallographic orientation. In these functional iron-based alloys, non-Joulian magnetostriction, in which volume is not conserved, was observed; generally, the Joulian magnetostriction in a volume is not altered by magnetic fields. As the magnetostrictive properties of these ironbased alloys are correlated to their elastic properties through the magnetoelastic effect, their elastic properties have also been investigated using single crystals of iron-based alloys. In the present paper, we discuss the characteristic features of the anisotropy of magnetostriction and inverse magnetostriction, which occur when magnetic fields and external stresses, respectively, are applied. In order to clarify the microscopic processes underlying the magnetostriction and inverse magnetostriction, the alterations in the magnetic domains by magnetic fields and external stresses were observed. The results revealed that the magnetic domain structure in the functional iron-based alloys is altered in a complex manner when applied with external fields. For example, it was demonstrated that unique motions of different types of Bloch domain walls are observed with the application of magnetic fields or external stresses along specific directions of single crystals of FeGa alloys. The characteristic features of the motion of the domain walls are likely to correspond to the occurrence of magnetostriction and inverse magnetostriction, in which magnetic fluxes are induced during alternative vibration.

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Contracting non-Joulian magnets

Cited by 6 publications

References 20 publications

Magnetic Domain Structures in Fe-Ga Alloys

Magnetic Domain Structures in Fe-Ga Alloys

Non‐Joulian Magnetostriction and Non‐Joulian Magnetism

Anisotropy of Magnetostriction of Functional BCC Iron-Based Alloys

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