Bulk and Interfacial Effects in the Co/NixMn100−x Exchange‐Bias System due to Creation of Defects by Ar+ Sputtering

Abstract

Research on ultrathin magnetic layers and layered materials has reached an enormous impact, both scientifically and economically, with respect to applications in magnetic data storage technology, as sensors, or for future electronics utilizing the spin rather than the charge of electrons, the so-called "spintronics". [1][2][3][4] The physical size of a bit of information in magnetic data storage is already in the nanometer regime and is still shrinking, following the everincreasing demand for higher recording densities. Very soon the dimension of the recording bit will reach the sub-10 nm range. This poses formidable challenges to the read sensors. One ingredient of hard disk read sensors are magnetic layered systems in which ferromagnetic (FM) and antiferromagnetic (AFM) materials are in contact. [5] They show the exchange bias (EB) effect, which has received increased attention during the past decades. [6][7][8][9][10][11] It manifests itself in a shift of the magnetic hysteresis loop of the FM layer along the field axis. [12] Although reported first in 1956, [13] it was only in the mid-1990s that it shifted into the center of interest, triggered by applications of FM/AFM heterostructures for tailoring the magnetic properties of magnetoresistive devices. The past years have seen significant advances toward an explanation of the effect, however, a fundamental microscopic picture of the origin of the unidirectional magnetic anisotropy present in the EB effect is still missing.The occurrence of EB requires two basic ingredients: a magnetic interaction between FM and AFM spins at the interface, and a pinning of magnetic moments against the reversal of the FM-layer magnetization by the external magnetic field inside the AFM layer. As in AFM materials the direction of the spins varies on the length scale of single atomic distances, a thorough characterization of the atomic structure of the films and their interface is mandatory for fundamental investigations into the effect. In the commonly used polycrystalline systems prepared by sputtering techniques this is naturally not the case. A promising approach is the investigation of single-crystalline systems. [14][15][16][17][18][19] In such systems, it is shown, for example, that the magnetic coupling between AFM and FM layers is due to

Growth of MnxAu1−x Films on Cu(001) and Ag(001) Single‐Crystal Substrates

“…While pure Mn does not exhibit MEED oscillations on Cu(001), it does show oscillations on Au(001). [ 39 ] In the case of on Cu(001) with x around 0.85, we have the situation that although there are no LEED patterns, which indicates the absence of long‐range crystallographic order in the films, MEED shows intensity oscillations with monolayer periodicity. One explanation could be that on top of the first, flat monolayer of Cu–Mn–Au alloy, which grows epitaxially with the lateral lattice constant of Cu(001), there is local layer‐by‐layer growth of Mn–Au, which then, due to the large lattice mismatch to Cu(001), exhibits only short‐range lateral crystallographic order.…”

Growth, Structure, and Magnetic Properties of Artificially Layered NiMn in Contact to Ferromagnetic Co on Cu3Au(001)

“…We define as the blocking temperature for exchange bias the temperature below which the exchange–bias field deviates significantly from zero. [ 20 ] The blocking temperatures of the ALF and the disordered alloy samples are indicated by arrows with dotted and solid lines, respectively. The blocking temperatures of the ALF are distinctly higher than the ones of the corresponding disordered alloy films.…”

“…The two metallic elements Ni and Mn were selected in our work because they are well investigated as single‐crystalline AFM systems in the form of disordered alloys (). [ 20–26 ] Tetragonally distorted NiMn‐disordered alloys grow in different directions on two different single crystalline substrates. On Cu(001), they grow along their a axis, while on , the growth is along the c axis, yielding a uniform structural domain.…”

“…[ 25,27 ] shows layer‐by‐layer growth on . [ 25 ] On top of each film 10 ML ferromagnetic (FM) Co is deposited, which grows epitaxially on top of the or the Mn AFM layers [ 20,25,27 ] and exhibits an in‐plane easy axis of magnetization. [] multi‐stacks with n = 1 ML and m between 1 and 3 ML were prepared with total thicknesses of 10, 12, 15, and 20 ML ( Figure 1 ).…”

Modulation of Exchange Bias in La0.35Sr0.65MnO3/La0.7Sr0.3MnO3 through Volatile Polarization of P(VDF‐TrFE) Gate Dielectric

“…Recent studies on epitaxial systems suggested that bulk AF magnetic structures play a crucial role in determining EB. [5][6][7][8][9][10][11][12] For example, the domain state model [13] theorizes that bulk AF domain structures are stabilized by nonmagnetic defects when it is field cooled below the Néel temperature (T N ), and these domains carry pinned uncompensated magnetic spins and result in EB of the FM layer.…”