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A primary method of characterizing the magnetic properties of a sample is to measure its magnetization while gradually varying an applied ambient magnetic field between large positive values and large negative values. The change in magnetization with field can be used to map the magnetic hysteresis loop of the sample, which defines some of its bulk magnetic properties (Figure 1).

Each sample, however, is actually composed of a population of magnetic grains and domains, which may vary in their magnetic properties and which may interact with their neighbors. The micromagnetic properties of these populations, such as the distribution of micro-coercivities and the magnetic interactions or biases, can be mapped by probing the interior of a hysteresis loop with a series of partial hysteresis curves referred to as first-order reversal curves (FORCs) [Mayergoyz, 1986; Pike et al., 1999] (Figures 1 and 2). These properties can then be used in various ways ranging from characterization of the magnetic composition, grain size, and concentration of samples to understanding the mechanisms of magnetic acquisition [e.g., Pike et al., 1999,2001; Roberts et al., 2006; Carvallo et al., 2006; Muxworthy et al., 2005].