Magnetic moment distribution in nanosized antiferromagnetic NiO

Abstract

Nanosized antiferromagnets show anomalously large magnetization and superparamagnetism, having complicated magnetic properties due to a competition between core and surface spins in addition to the surface-induced effect, the finite size effect, and the magnetic moment distribution. A significant distribution of magnetic moments, which are responsible for the superparamagnetism, can also exist in real ensembles of nanoparticles, making the analysis of magnetization difficult. It has been a key issue for the understanding of the complicated magnetic property to correctly separate a superparamagnetic component from an antiferromagnetic component that linearly depends on magnetic fields in the observed magnetization. Here, we report the separation of these two components observed in the magnetization of antiferromagnetic NiO nanoparticles by applying the scaling law in the magnetization of superparamagnets. The distribution of the magnetic moment was taken into account without a priori assumption of the distribution function. The magnetic moments causing superparamagnetism had a bimodal distribution with different mean values. The contribution of the two different superparamagnetic components could thus be newly clarified and was ascribed to the uncompensated spins in the core and on the surface. The magnetic structure that leads to the bimodal distribution is discussed in light of the inhomogeneity of the surface structure.

Features of the quasi-static and dynamic magnetization switching in NiO nanoparticles: Manifestation of the interaction between magnetic subsystems in antiferromagnetic nanoparticles

“…This is reflected in a drastic difference between the magnetic properties of bulk antiferromagnets and AFM nanoparticles. The main feature of AFM nanoparticles is the occurrence of an uncompensated magnetic moment; in these materials, in fact, a ferromagnetic (FM) subsystem forms [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], which becomes especially important in particles 10-20 nm in size and smaller. This significantly broadens the range of possible applications of AFM nanoparticles, which, in contrast to the bulk analog or submicron AFM particles, are already «magnetic».…”

Unveiling the correlation between structural and magnetic ordering in nano Co1−xNixTeO4

“…4(a, d and g), a linear M – H is due to paramagnetic behavior. A weak FM behavior at low temperatures and paramagnetic behavior at high temperatures in these nano-sized pristine compounds can be understood in terms of blocked spins (in the superparamagnetic state) overcoming the energy barrier using the thermal energy at high temperatures (NiO, 21 CuO 22 and MnO 23 ). In contrast, the calcinated crystalline nanoparticles of MTO show AFM order under H = 0.…”

Magnetic Properties of Two‐Line Ferrihydrite Nanoparticles

“…If a particle consists of spins then there will be approximately uncompensated spins. [ 43–48 ] Total spins in a particle are proportional to particle volume V . So for spherical particles , where C is a material‐dependent constant.…”

“…If a particle consists of N s spins then there will be approximately ffiffiffiffiffiffi N s p uncompensated spins. [43][44][45][46][47][48] Total spins in a particle are proportional to particle volume V. So for spherical particles μðDÞ ¼ CD 3=2 , where C is a material-dependent constant. Value of this constant can be calculated with the help of the crystal structure of the material.…”