What is VARIFORC? VARIFORC is the first software package dedicated to advanced processing of first-order reversal curves (FORC). It offers state-of-the-art processing tools, such as weighted polynomial regression, heteroscedastic error calculations, variable smoothing for optimal noise suppression, manual/automatic handling of problems related to high-resolution features (ridges, rectangular hysteresis loops with very steep flanks), as well as special tools for coercivity analysis and central ridge processing. VARIFORC supports standard processing tasks (e.g., import single/multiple measurement sets, correct drift and outliers, calculate the FORC diagram), customized plotting (contour lines, significance tests), and modeling (e.g., linear combination of FORC datasets/diagrams, ridge extraction). The new interactive user interface enables inexperienced users to obtain their first results within minutes without previous FORC processing knowledge.
Applications. VARIFORC offers unique features suited for general-purpose and special applications. Special applications include, but are not limited to: • processing noisy measurements obtained from weak specimens (e.g., sediments and thin films) • processing measurements containing non-regular features such as first- and second-derivative discontinuities (e.g., collective nucleation/denucleation processes, magnetic viscosity, and non-interacting particles) • seamless combination of measurements (e.g., stacking and differences) • calculation of coercivity distributions • isolation of specific signatures (e.g., the central ridge) • quantitative analyses (i.e., magnetizations corresponding to specific FORC signatures).
Requirements. VARIFORC runs with Mathematica (student license: 140 € or 150 US$) and Mathematica CDF PlayerPro (general license: 205 € or 205 US$) on Windows, Linux, and Mac. Previous knowledge of Mathematica software is not required. See the user manual about installation and further details.
Documentation. VARIFORC comes with a very detailed user Manual, a general FORC tutorial, and several downloadable application examples. Each example focuses on materials with specific processing requirements (e.g., magnetofossil-bearing sediments and volcanic rocks with pseudo-single-domain signatures). Examples are also dedicated to specific processing problems (e.g., first- and second-derivative discontinuities, and correction of first measurement points). Each application example provides sets of VARIFORC processing parameters that can be used to analyze FORC measurements of similar materials.
The following VARIFORC modules are currently available:
ImportFORC: import and correct single/multiple FORC measurements
• Supports FORC data formats generated by PMC MicroMag magnetometers, including legacy ones • Correct measurement drift, transient instabilities, and outliers • Checks and optionally corrects problems with first and last measurement points • Manage field/magnetization units and normalize measurements by mass, volume, and area • Average multiple measurements for noise reduction • Calculate hysteresis parameters with manual or automatic paramagnetic corrections • Plot and export corrected FORC measurements and measurement differences for further processing.
CalculateFORC: calculate and plot FORC diagrams
• Free choice of the FORC region to be calculated, including measurement points located outside the standard rectangular FORC space • Automatic/manual choice of the output grid on which the FORC function is computed (for seamless combination with other FORC data) • Weighted and unweighted polynomial regression • Conventional FORC processing with constant smoothing factors • Advanced FORC processing based on variable smoothing for optimal noise suppression • Processing options for challenging datasets (e.g. vertical ridge, central ridge, very squared hysteresis) • Mean field correction (new in version 2.0) • Heteroscedastic error calculation and significance estimates • Automatic calculation of FORC-derived magnetizations and coercivity distributions • Export FORC matrices and coercivity distributions with metadata for further processing with VARIFORC or third-party software.
PlotFORC: plot publishing-quality FORC diagrams with post-processing flexibility
• Choose the FORC region to be plotted and zoom on details such as the central ridge region • Use specially developed color scales for optimal representation of high- and low amplitude details • Draw contour lines automatically or manually at any specified level and exclude small contour loops generated by measurement noise • Draw contours enclosing significant regions of the FORC diagram • Plot FORC diagrams with normalized vertical profiles for estimating the vertical width (useful for interaction field reconstruction and a selection tool for absolute paleointensity determinations) • Export publishing-quality FORC diagram images (vector and raster formats) • Enter plotting parameters (e.g. contour levels) as percentace of the maximum FORC amplitude for better comparison between diagrams (new in Version 2.04).
IsolateCR: process central ridges
• Isolate central ridges from other FORC contributions • Plot the central ridge and other FORC contributions individually with corresponding heteroscedastic error estimates • Calculate the central ridge coercivity distribution and plot it together with other FORC-derived coercivity distributions • Export FORC components and coercivity distributions for further processing with VARIFORC or third-party software.
LinearCombineFORC: calculate linear combinations of FORC data
• Calculate any linear combination of an arbitrary number of FORC datasets (corrected measurements or FORC matrices) • Average measurements obtained with different FORC protocols • Subtract a background (e.g. sample holder) • Isolate the contribution of specific minerals by calculating measurement differences upon selective magnetic/chemical extraction.
Current version: 4.00 (released 25.08.2017). An interactive user interface has been introduced, which enables inexperienced users to obtain their first results without previous FORC processing knowledge. The user interface can handle complex cases, enabling the identification of problems such as measurement and processing artifacts, and supporting the choice of best processing options. The new VARIFORC sotfware will be presented at the IASPO-IAMAS-IAGA joint assebly in Cape Town (27 August - 1 September 2017).
Version: 3.02 (released 17.04.2017). Improved importing capabilities (files without calibration measurements) and improved handling of extremely constricted hysteresis. A bug that prevented the upload of source code files when using the CDF Player has been removed.
Use the full VARIFORC functionality without any previous knowledge: version 4 with interactive step-by-step assistant is on the way. Stay tuned with the VARIOFORC-RSS-Feed .