Non‐Joulian Magnetostriction and Non‐Joulian Magnetism

Abstract

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.

Influence of long- and short-range chemical order on spontaneous magnetization in single-crystalline Fe0.6Al0.4 compound thin films

“…The relationship between the chemical order and the magnetism in Fe 1−x Al x has been intensively studied in terms of both fundamental solid-state physics and applied material science, e.g. magnetostrictive materials [26][27][28] and structural materials with the low density and the high corrosion resistance [14][15][16]29]. Besides, the Fe-Al compounds retrieved the attention in the field of spintronics since the partially ordered or fully disordered Fe 1−x Al x showed the relatively high anomalous Hall angles (∼3%) without using the heavy-metal elements [19,24,25,30].…”

Demagnetization Effect on the Magnetoelectric Response of Composite Multiferroic Cylinders

“…In the direct sense, the geometry changes in the direction of the applied magnetic field in what is referred to as the Joule magnetostriction [1]. However, the application of a magnetic field also induces a change in the state of magnetization, resulting in a change in the volume (i.e., volume magnetostriction) and the elastic modulus (commonly denoted as the ∆E effect) [1,6]. When considering the converse coupling paradigm, there are inversely analogous effects: the Villari effect, the Nagaoka-Honda effect, and magnetically induced changes in the elastic response, respectively [1].…”

“…The outcomes of these research efforts further culminate the justification for describing the concentric ring structure as complex. For example, composite ring structures have been experimentally studied, which consisted of an outer piezoelectric cylinder (PZT, lead zirconate titanate) and an inner piezomagnetic ring (Terfenol-D, an alloy of iron, terbium, and dysprosium) operating under the converse magnetoelectric coupling paradigm [5][6][7][8][9][10][11]. Experimentally, it also has been shown that the direction of polarization of the piezoelectric cylinder, the quality and method of interfacing the cylinders, the direction and magnitude of applied bias magnetic field, the frequency and magnitude of the electric field, and the duration of loading influence the overall response symbiotically [5][6][7][8][9][10][11].…”

Magnetic Domain Structures in Fe-Ga Alloys

“…Chopra also demonstrated in a slow cooled sample of Fe73.9Ga26.1 that the domain structure formed a perfect mirror image across the whole sample with a bisector moving down the centerline [54]. This sample demonstrated volume conserving magnetostriction.…”