Ceria (CeO₂) is a promising dilute magnetic semiconductor. The ferromagnetic order has proven to be an surface effect.

An effective method to probe local magnetostatic properties in a nanometric FePd antidot array F

First-order reversal curve diagrams have been used to investigate magnetostatic interactions and average coercivity of individual wires in soft ferromagnetic uniform length nanowire arrays. We present a method for identifying these physical parameters on the out-of-plane first-order reversal curve diagrams: the position of the irreversible part on the critical axis is a good approximation to the average value of the nanowire coercivity and the maximum interaction field is equal to the interaction field at saturation. Their dependence upon material (CoFeB and Ni) and nanowire length are presented. The magnetostatic interactions increase linearly with length, in agreement with a model developed previously. The global array coercivity, obtained from magnetization curves, is generally lower than the apparent average coercivity for individual nanowires. This coercivity reduction increases linearly with the magnetostatic interactions. The general shape of the out-of-plane first-order reversal curve diagrams is compared with those obtained from a theoretical moving Preisach model.

A new approach to the quantitative and physical analysis of first-order reversal curve (FORC) diagrams is presented. Each hysteron in the FORC method represents a magnetic cluster. Starting with a model for a ferromagnetic, isotropic, and monodomain sphere, and adding anisotropy and domain structure, three different types of “basic hysterons” are obtained: vertical reversible and irreversible, and linear. The FORC diagrams of basic hysterons with a mean interaction field were obtained by simulation. From them, the relationships between the characteristics of the hysterons and the FORC distribution function were extracted. Different sets of hysterons can lead to the same FORC distribution function. A positive mean interaction field tends to merge the hysterons on the FORC diagram, while a negative mean interaction field introduces repulsion between them.

Arrays of Ni/Cu multilayer nanowires were fabricated by electrodeposition into alumina templates (pore diameter = 175 nm, interpore distance = 300 nm), with an Ni disc thickness between 20 and 50 nm, and a Cu thickness between 10 and 35 nm. Vector major hysteresis loops were measured with an out-of-plane (along the nanowire axis) and inplane (perpendicular to the nanowire axis) applied field. During the magnetization reversal, we did not observe any net component of transverse magnetization (M_y) , perpendicular to the applied field H_x. Extrapolated first-order reversal curve (FORC) diagrams were measured, out-of-plane and inplane. While the major hysteresis loops of all arrays have similar shapes, their FORC diagrams reveal distinct patterns, suggesting different magnetic behavior. The magnetic anisotropy can be controlled by the ratio of Cu to Ni thickness, the nanowire axis becoming harder as the ratio increases. In the out-of-plane direction, the maximum interaction field is proportional to the Ni thickness. The FORCs show evidence of a large coercive field distribution, which we attribute to the smaller interaction fields in the nanodiscs along the edges of the samples. In the inplane direction, depending upon the easy axis direction, there can be a mixture of nanodiscs reversed by coherent and incoherent rotation, or by incoherent rotation only.