摘要:

Ferromagnetic domains of a single crystal of neodymium‐iron‐boron, Nd2Fe14B (one of the strongest permanent magnetic materials known) are imaged by focusing a beam of photoelectrons with electrostatic optics in a photoelectron emission microscope. Photoelectrons emitted from the surface are deflected laterally into two opposite directions by stray magnetic fields that exist above the domains. The photoelectron beam is partially split into two. Magnetic contrast is produced by blocking part of the beam and imaging with an edge of the beam. The magnetic contrast mechanism appears to be similar to the type I magnetic contrast mechanism known from scanning electron microscopy, in which stray magnetic fields above the ferromagnetic domains deflect secondary electrons either towards or away from the electron detector. Upon heating the sample above the Curie temperature, the ferromagnetic domains gradually disappear, as expected for a second order phase transition. They reappear upon cooling.

ISSN:0734-211X    

DOI:10.1116/1.589074

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The primary objective of this study is to determine the effect of silicon wafer processing parameters on giant magnetoresistance (GMR). Thermally oxidized silicon wafers serve as substrates for alternating layers of NiFeCo and Cu (2.0–2.5 nm). SiO2films prepared in the laboratory are loaded into the sputtering chamber along with commercially oxidized wafers for comparison purposes. Four process parameters are systematically varied—oxidation method, postoxidation anneal (POA), oxide thickness, and oxidation temperature. Preliminary results indicate the two most influential processing parameters are the method of oxidation (dry oxygen or wet steam) and a POA. In contrast, GMR values do not seem to vary greatly for various oxidation or POA temperatures in the range 800–1000 °C. We present GMR results of NiFeCo/Cu multilayers on oxidized silicon substrates formed by various processing methods. GMR is observed for all films, with the magnitude of the effect increasing for substrates oxidized by ‘‘wet’’ methods and oxidized substrates that include a POA (1000 °C, nitrogen atmosphere, 20 min) previous to sputter deposition of the multilayers. Our data suggest that the GMR of the multilayer stack is sensitive to changes at the Si–SiO2interface.

ISSN:0734-211X    

DOI:10.1116/1.589075

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The local spin density approximation (LSDA) is used to investigate the interrelationships between electronic properties, magnetism, structure, and transport in La1−xCaxMnO3. The LSDA is shown to provide a realistic description of the endpoint compounds, including magnetic and structural symmetry. Mn–O hybridization is strong and spin dependent. Supercell calculations forx=1/4 andx=1/3 yield ferromagnetic configurations. Strong local La–Ca cation effects are found, which lead to localization of the low density of minority spin carriers in this regime. Implications of this effectively half‐metallic electronic structure are discussed.

ISSN:0734-211X    

DOI:10.1116/1.589076

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

We evaluate the possibility of using dichroic electron energy loss spectroscopy (DEELS) as an alternative to x‐ray magnetic circular dichroism (XMCD). It is well known that electron energy loss spectroscopy and x‐ray absorption spectroscopy provide similar information. A simple semiclassical model suggests that reflection DEELS might have a magnetic sensitivity similar to that of XMCD. This sensitivity will be reduced, however, by multiple scattering of the probe electron before and after the energy loss event. Thus, it is difficult to predict the magnitude of the DEELS effect. Experiments were performed at theLedges of polycrystalline Fe, Co, and Ni thin‐film samples preparedinsituwith a uniaxial magnetic bias. Even in these most favorable cases, the DEELS effect is limited to less than one‐tenth of related effects in XMCD.

ISSN:0734-211X    

DOI:10.1116/1.589078

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

A new group of techniques predicated on the availability of a tunable source of circularly polarized soft x‐rays show tremendous potential for advancing the understanding of magnetic nanostructures. These techniques involve use of circularly polarized radiation as probes in x‐ray absorption and x‐ray photoemission and photoelectron diffraction studies, and provide unique information about the element specific magnetic moments and magnetic structure of thin films, interfaces, and surfaces. Examples of each technique will be discussed with emphasis given to the recently demonstrated first observation of spin‐dependent photoelectron diffraction using circularly polarized x‐rays. This technique promises the direct, element specific determination of local magnetic structure on an atomic scale, and will be of tremendous utility in the effort to establish structure‐property relationships in magnetic nanostructures. Circularly polarized x‐rays are used to produce spin‐polarized photoelectrons from the Fe 2pspin‐orbit doublet. Intensity asymmetries of up to ∼3% are observed for the 2p3/2sublevel. These asymmetries depend on the relative orientation of the x‐ray polarization vector and the sample magnetization as well as upon the photoelectron kinetic energy and emission direction. Multiple scattering calculations are found to reproduce both the observed energy and angular asymmetry variations. Strategies to increase the measured effect are also discussed.

ISSN:0734-211X    

DOI:10.1116/1.588799

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Calculations of structural stabilities for thin iron layers as grown on Cu(001) are reported. It is found that a free‐standing fcc(001) monolayer is unstable with respect to 3×1 and 4×1 distortions. The former instability is directly related to the Pitsch transformation from fcc(001) to bcc(110), and calculations along the path find bcc(110) as the stable structure. Inclusion of the Cu substrate in the calculation tends to stabilize fcc(001). The calculated instabilities are of similar form to the superstructures observed for Fe grown on Cu(001). The relation to the experimental situation is discussed.

ISSN:0734-211X    

DOI:10.1116/1.588800

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The structural and magnetic properties of metastable face‐centered‐cubic (fcc) Fe thin films on fcc Co(100) substrate were studied using wedged samples. fcc Co(100) was chosen for the substrate because it is structurally very similar to Cu(100) but is ferromagnetic at room temperature. Reflection high energy electron diffraction and low energy electron diffraction characterizations confirm that epitaxially grown (MBE) Fe on Co(100) is structurally very similar to Fe on Cu(100): face‐centered‐tetragonal (fct) fordFe<6 ML, fcc for 6 ML

ISSN:0734-211X    

DOI:10.1116/1.588801

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The magnetic structure of nanoscale alloy films has been probed using the magnetic x‐ray linear dichroism in photoelectron spectroscopy and magnetic x‐ray circular dichroism in x‐ray absorption spectroscopy. FeNi and CoFe epitaxial films were grown on Cu(001),insituand using MBE techniques. Because soft x‐rays were used to probe the 2pand 3pcore levels, both elemental selectivity and magnetic sensitivity were achieved simultaneously. Correlation of these magnetic techniques with compositional and structural information will be done. Ultimately, from studies such as this a complete determination of the structure‐property relationships will be achievable.

ISSN:0734-211X    

DOI:10.1116/1.588802

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

The polar ellipticity spectra of the interfaces of epitaxial Fe/Au(001) wedges have been measured. The interface spectra resemble neither the reflection Faraday spectrum of Au nor the thin‐film spectra of thin Au sandwiched Fe. The existence of low and high energy peaks suggest that magneto‐optical transitions occur from and to the interface states.

ISSN:0734-211X    

DOI:10.1116/1.588803

出版商:American Vacuum Society    

年代:1996

数据来源: AIP

摘要:

Ultrathin Co films were epitaxially grown on a Cu(001) surface with different initial roughness created by Ar ion sputtering. The roughness of the Cu substrate and the Co film were characterized by high resolution low energy electron diffraction. The measured angular profiles were compared with a diffraction theory for rough surfaces and the roughness parameters were extracted quantitatively. Magnetic hysteresis loops of these characterized films were measured by surface magneto‐optic Kerr effect. The hysteresis loop shape and loop area can be related to the nanoscale roughness in the Co films. For the roughest film with interface width ≊1.2t, wheretis the single atomic step height, the magnetization is reduced several fold compared with that of smooth films with interface width ≊0.5t. Also, the coercivity in the roughest film is the highest and there exists a wide range of nucleation centers and coercive fields for magnetic domain reversals. These are related to the high step density in the rough substrate as the pinning centers. The hysteresis loop changes its shape and area under a sinusoidal external magnetic field as functions of frequency and field amplitude for all films. For the smooth films in the low frequency and low field regimes the loop area shows a 2/3 power law scaling behavior. The 2/3 value of scaling exponents are consistent with the prediction of a dynamic mean field theory with a double‐well energy barrier. For a film with the same interface width but different step density and lateral correlation length the scaling exponents deviate from 2/3 value drastically.

ISSN:0734-211X    

DOI:10.1116/1.588804

出版商:American Vacuum Society    

年代:1996

数据来源: AIP