Search

Ultrathin CoFeB/MgO/CoFeB system with perpendicular magnetic anisotropy is a promising candidate for the high density magnetic random access memory. However, a dipolar interaction between the CoFeB layers may introduce a minor loop shift (Hs) and causes uncertainty during the operation. In this report, we systematically studied the dipolar effect in these structures and found that the coupling may be either ferromagnetic or antiferromagnetic (15 Oe>Hs> - 15 Oe) depending upon the CoFeB thickness (0.9-1.4 nm). A modified Fabry-Perot model, which accounts the Bloch wave interference, may explain the present observations of the dipolar effect in the perpendicular junctions of CoFeB/MgO/CoFeB. [ABSTRACT FROM AUTHOR]

Mn2.5Co0.5O4 films are grown on MgO(001) and (011) substrate by molecular beam epitaxy. Detailed structural and magnetic analyses are carried out by x-ray diffraction and magnetization measurements. The reduction of the lattice parameter c/a* ratio and the enhancement of the Curie temperature (from 43 to 66 K), due to the weakening of the Jahn-Teller effect, are observed. In addition, thermomagnetic reversibility is observed at lower temperature and low external filed indicating the existence of local canting states. The randomness of Co cation and uniaxial anisotropy further enhance the local canting effect. An H-T phase diagram is mapped out, which indicates a short rang order state in the temperature 66-85 K separating the ferrimagentic and paramagnetic phases. [ABSTRACT FROM AUTHOR]

MgO-based CoFeB structure is one of the typical layered structures with strong perpendicular magnetic anisotropy (PMA). However, the physical properties depend critically upon the sequence of the metal protection layer, and the top structure is especially sensitive to the thickness of the metal layer. In this paper, the cap layer effect on PMA in top structures of Si(substrate)/MgO/CoFeB (1–1.7 nm)/Ta (1–5 nm) is systematically investigated. An inverse correlation between the interface anisotropy constant (Ki) and the thickness of the magnetic dead layer (MDL) is identified. Ki decreases from 2.2 to 1.4 erg/cm2 while MDL increases from 0.1 to 0.6 nm, both showing a nonlinear dependence upon the Ta thickness with an abrupt change at Ta ~ 1.5 nm. These observations indicate that the cap layer effect on both PMA and MDL originates from the chemical deterioration at MgO/CoFeB and CoFeB/Ta interfaces by Ta diffusion. [ABSTRACT FROM AUTHOR]

The present study grows a series of Fe3-xMgxO4 (0≤x≤1.5) films and systematically measure both structure and magnetization of these films. These films are grown on MgO and SrTiO3 (STO), which have small (∼-0.3%) and large (∼7.5%) lattice mismatch in order to have either strained or relaxed films, by plasma-oxygen-assisted molecular beam epitaxy, respectively. X-ray diffraction (XRD) is carried out to analyze the crystalline structure. Saturation magnetization (Ms) of pure Fe3O4 (x=0) on both substrates is ∼500 emu/cm3, which is consistent with the bulk value. However, Ms has a fast decrease with increasing x for the films grown on MgO(001), from 340 to ∼100 emu/cm3 in the region of 0.33 for x>1.35. On the other hand, Ms remains unchanged with x increasing from 0.3 to 1 for the film grown on STO. With x>1, Ms drops abruptly to ∼100 emu/cm3, which is comparable to Ms of the film grown on MgO. The discrepancy in Ms of Fe3-xMgxO4 film grown on MgO and STO may imply that the cation distribution of these films may be fundamentally different. Possible cation distribution and the substrate strain effect will be discussed. [ABSTRACT FROM AUTHOR]

A series of ferrimagnetic/ferrimagnetic Fe[SUB3]O[SUB4]/Mn[SUB3]O[SUB4] superlattices are grown on MgO(001) and (011) substrates by plasma-oxygen-assisted molecular beam epitaxy. The thickness of the Fe[SUB3}O[SUB4] layer is 4 nm and the thickness of Mn[SUB3]O[SUB4] is varied from 1 to 16 nm and the total thickness of these films is between 100 and 200 nm. The magnetization as a function of temperature and external field (parallel to the film surface) is measured in the range of 4 -300 K and -50-50 kOe. The main magnetic response of the superlattices with thicker Mn[SUB3]O[SUB4] layers show compensation points ∼39K) and spin-flop phases at a high external field (>15 kOe) indicating the net moments in Fe[SUB3]O[SUB4] and [Mn[SUB3]O[SUB4] are antiparallel at the interface. The magnetic response of the superlattices with thinner Mn[SUB3]O[SUB4]layers show regular ferromagnetic hysteresis and temperature curves indicating the net moments in Fe[SUB3]O[SUB4] and Mn[SUB3]O[SUB4] are parallel at the interface. A transition of the magnetic coupling between Fe[SUB3]O[SUB4] and Mn[SUB3]O[SUB4] from antiparallel to parallel is clearly observed when the Mn{SUB3]O{SUB4] layer thickness is less than 4 nm. A domain-wall-like configuration is believed to form at the interface to maintain the antiparallel state of Fe[SUB3]O[SUB4]/Mn[SUB3]O[SUB4]. When the layer thickness reduces below certain thickness the domain-wall-like configuration no longer exists and a parallel state is preferred. A model of the domain-wall-like configuration between Fe[SUB3]O[SUB4] and Mn[SUB3]O[SUB4] is discussed. [ABSTRACT FROM AUTHOR]

[Fe[sub 3]O[sub 4](40&Aaring;)/Mn[sub 3]O[sub 4](160 Å)][sub × 10] superlattice is grown on MgO(110), and its in-plane angular-dependent magnetic response is studied. Magnetic compensation and spin-flop state are observed at ∼42 K and external field > 15 kOe when the magnetic measurement is along the [1-10] direction. These features disappear when the measurement is along the [001] direction. This strong anisotropic effect may originate from the tetragonal structure of Mn[sub 3]O[sub 4] whose magnetic easy axis is in the a-b plane and hard axis is perpendicular to the a-b plane. This study demonstrates that the compensation point and spin-flop phase transition both are orientationally dependent in an antiparallel-coupled magnetic layer system if there is at least one constituent component with strong magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the growth mode and structural characterization of nickel oxide and iron[sub3] oxide[sub4] superlattices. Preparation of the study samples; Analysis of the interplay between magnetic coupling and structural strain in superlattices of oxide ferrites; Magnetic characteristics of the superlattices.