Obtaining an estimate of the relative proportion of superparamagnetic (SP) to stable single-domain (SSD) particle sizes in a material can be useful in evaluating environmental conditions in natural materials, or in understanding the homogeneity of particle size and the degree of agglomeration in synthesized particles. Frequency dependent magnetic susceptibility is one of the most common methods used to identify SP particles in a material. The ability to detect SP particles, however, will be dependent on the field frequencies that can be applied. This study is concerned with evaluating three methods to estimate the SP content in a mixture of SSD and SP magnetite. We examine the use of the Day-Dunlop plot, first-order reversal curves (FORC) and principal component analysis (PCA), and the relationship between the reversible and irreversible magnetization as methods to evaluate qualitatively the relative contributions of SSD and SP magnetite in a material. Two series of mixtures of coated nanoparticles with a mean diameter of 20 and 11 nm are used as the SP end member and magnetosomes or intact magnetotactic bacterium of Magnetospirillum gryphiswaldense as the SSD end member. The Day-Dunlop plot tracks the progressive change in hysteresis properties with growing SP concentration. PCA of FORC data is sensitive in detecting differences in the SP component, when the SP particle size are not too small; otherwise the ratio between the reversible and irreversible magnetization can better assess differences. The results from the series are used to evaluate the relative SP content in three further sets of samples: biological tissue, synthetic nanoparticles, and samples from natural environments, to assess the strengths and weaknesses in each approach.

获得材料中超顺磁性（SP）与稳定单畴（SSD）粒径的相对比例的估计值可用于评估天然材料的环境条件，或有助于理解粒径的均一性和团聚程度。合成粒子。频率相关的磁化率是用于识别材料中SP粒子的最常见方法之一。但是，检测SP粒子的能力将取决于可以应用的场频。这项研究涉及评估三种方法来估算SSD和SP磁铁矿混合物中的SP含量。我们研究了Day-Dunlop图，一阶反转曲线（FORC）和主成分分析（PCA）的使用，以及可逆和不可逆磁化之间的关系，作为定性评估材料中SSD和SP磁铁矿相对贡献的方法。将平均直径为20和11 nm的两种涂覆纳米颗粒的混合物系列用作SP末端成员和磁小体或完整的趋磁细菌灰质螺旋体作为SSD的最终成员。Day-Dunlop图跟踪随着SP浓度的增加，磁滞特性的逐步变化。当SP粒度不太小时，FORC数据的PCA对检测SP成分的差异很敏感；否则，可逆和不可逆磁化强度之比可以更好地评估差异。该系列的结果用于评估另外三组样品中的相对SP含量：生物组织，合成纳米颗粒和自然环境中的样品，以评估每种方法的优缺点。