Dynamic magnetization of ε-Fe2O3 in pulse field: Evidence of surface effect

Abstract

The magnetization dynamics of ε-Fe2O3 nanoparticles with an average size of about 9 nm is investigated. From comparison of the hysteresis loops obtained in quasi-static conditions and under pulse fields with amplitudes up to 200 kOe and pulse lengths 8–32 ms, it follows that the effective coercivity increases considerably with the variation rate of the imposed magnetic field. A theoretical explanation of this behavior is proposed. The model takes into account the superparamagnetic effects as well as the fact that magnetic anisotropy of the nanoparticles, along with the bulk term, includes a surface contribution. The latter, being of minor importance for the observed magnetic behavior of 25–100 nm particles, becomes essential when the particle size is below 10 nm. From the experimental data, a reference value of the surface anisotropy of nanodisperse ε-Fe2O3 is established, and evidence is presented to the effect that below 300 K this contribution does not significantly depend on temperature.

Crystal Structure and Magnetic Properties of ϵ‐RuxFe2‐xO3 Nanosize Hard Ferrite

“…Recently, e-iron oxide (e-Fe 2 O 3 )has drawn attention because it exhibits ah uge coercive field (H c ). [2][3][4][5][6][7] e-Fe 2 O 3 is ap olymorph of ferric oxide Fe 2 O 3 (a-phase, [8][9][10] b-phase, [11,12] g-phase, [13,14] e-phase, [2][3][4][5][6][7][15][16][17][18][19] and z-phase). [20] Due to its strong magnetic anisotropy, e-Fe 2 O 3 exhibits ferromagnetic ordering even in the single nanometer size (superparamagnetic limit = 7.5 nm), which is the smallest value among ferrites.…”

Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect

“…In addition, development of an optically transparent magnet is highly desirable for new applications, such as transparent electromagnetic wave-absorbing windows or magnetic color pigments for printers. In light of the above requirements, epsilon iron oxide ε-Fe 2 O 3 is an attractive material because it exhibits a large H c value at room temperature71819202122232425. In the present work, we develop a synthetic method for the preparation of single-nanosize ε-Fe 2 O 3 spherical particles.…”

Температурное поведение антиферромагнитной восприимчивости нано-ферригидрита из измерений кривых намагничивания в полях до 250 kOe

“…Для квазистатиче-ских магнитных измерений обычно используется зна-чение τ ∼ 10 1−2 s [1], что приводит к соотношению T B ≈ KV /25k B . При измерениях в импульсном поле знаменатель выражения (3) изменяется, что проявля-лось, например, в росте коэрцитивной силы наночастиц ε-Fe 2 O 3 при уменьшении периода импульса [38]. При τ ∼ 8 · 10 −3 s (время возрастания поля до 250 kOe) T B увеличится в ∼ 1.3 раза по сравнению с квазистатиче-скими магнитными измерениями.…”