Avoiding the zero-coercivity anomaly in first order reversal curves: FORC+

Abstract

In conventional FORC (First Order Reversal Curve) analysis of a magnetic system, reversible and low-coercivity irreversible materials are treated as being qualitatively different: the FORC distribution shows low-coercivity materials but completely hides reversible (zero-coercivity) ones. This distinction is artificial -as the coercivity approaches zero, the physical properties of an irreversible material change smoothly into those of a reversible material. We have developed a method (called FORC+, implemented in free software at http://MagVis.org) for displaying the reversible properties of a system (a reversible switching-field distribution, R-SFD) together with the irreversible ones (the usual FORC distribution), so that there is no sudden discontinuity in the display when the coercivity becomes zero. We will define a "FORC+ dataset" to include the usual FORC distribution, the R-SFD, the saturation magnetization, and what we will call the "lost hysteron distribution" (LHD) such that no information is lost -the original FORC curves can be exactly recovered from the FORC+ dataset. We also give some examples of the application of FORC+ to real data -it uses a novel complementary-color display that minimizes the need for smoothing. In systems which switch suddenly (thus having sharp structures in the FORC distribution) direct display of un-smoothed raw data allows visualization of sharp structures that would be washed out in a conventional smoothed FORC display. This is an expanded version of paper GG-05, MMM-Intermag 2019, with a discrete derivation of the FORC distribution (Eq. 1) and an additional example (Fig. 7).

Beyond the qualitative description of complex magnetic nanoparticle arrays using FORC measurement

“…To further suppress these limitations, we propose to decompose the irreversible and reversible switching fields (ISF and RSF, respectively) and only investigate the ISF distributions at the H=H r and H=0, figure 1(a). Note the ISF at H=H r (P Hr ) can be calculated by projecting the FORC heat-maps in H r axis [23,43,44] as it is the residual magnetic moment at the reversal field. An equivalent parameter to this is the backfield remanence coercivity (BRC), see figure 1(b), which is the ISF at H=0.…”

Realizing the Principles for Remote and Selective Detection of Cancer Cells Using Magnetic Nanowires

“…As mentioned above, the ISF signature is also a function of the interaction fields between the MNWs. The interaction field effect on ISF signatures is a broadening (increasing full width at half-maximum, FWHM) and a shift of the ISF peak field depending on the relative strength of the coercivity and interaction fields. − Here, the interaction fields were engineered by the MNW composition (determining the saturation magnetization) and the MNW diameter-to-interwire-distance ratio, which is the interpore distance of the biopolymers. For simplicity, we kept the interpore distances constant, 540 nm, for all biopolymers.…”

FeCo Nanowire–Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products

“…On the other hand, as explained above, the presence of ferrite particles may be reducing interwire demagnetizing fields with respect to the pure NW sample. More sophisticated characterization methods are needed to fully unravel this balance and the specific reversal mechanisms and switching events. ,− In any case, the derivatives in Figure d suggest that the internal fields and the particle arrangement created by the hard ferrite particles support the initial single-domain state inside the wires, which is likely responsible for the high squareness and H c of the composite magnet.…”

“…For this reason, shape anisotropy has been often employed as a tool to sustain a certain resistance to demagnetization in high-magnetization systems, for instance, by fabricating high-aspect-ratio transition-metal structures. , A great deal of work has been focused on Co nanowires (NWs) owing to the relatively large magnetocrystalline anisotropy of Co compared to other magnetic transition metals such as Fe and Ni. − Promising results ,, have been obtained in this system, including the fabrication of NW-only dense pellets with improved magnetic properties. , Fe, FeNi, and FeCo nanowires have been investigated as well. − They present larger magnetization and lower coercivity than Co, which makes them suitable for a wide array of application sectors that include biomedical, − environmental (in this case, ferrite NWs), and sensors, among others. In addition, arrays of low-coercivity NWs are excellent systems to study and analyze the complex hysteretic and reversal mechanisms of ferromagnets. ,− …”