To provide new alloy nanocrystals which can be easily and efficiently produced while allowing the production cost thereof to be reduced, can be easily dispersed into a solvent stably over a long period, and can be suitably used as a high density magnetic recording medium, a magnetoresistive element, a catalyst for an electrode of a fuel cell, a heat generating element for magnetic thermotherapy or the like when being arranged on a substrate.

The alloy nanocrystal includes: a core part containing at least one kind of transition metal element selected from among Fe and Co and at least one kind of noble metal element selected from among Pt and Pd; and long chain saturated fatty acid stuck to the surface of the core part.

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