Switching a magnetic vortex by interlayer coupling in epitaxially grown Co/Cu/Py/Cu(001) trilayer disks

Epitaxial Py/Cu/Co/Cu(001) trilayers were patterned into micron sized disks and imaged using element-specific photoemission electron microscopy. By varying the Cu spacer layer thickness, we study how the coupling between the two magnetic layers influences the formation of magnetic vortex states. We find that while the Py and Co disks form magnetic vortex domains when the interlayer coupling is ferromagnetic, the magnetic vortex domains of the Py and Co disks break into anti-parallel aligned multidomains when the interlayer coupling is antiferromagnetic. We explain this result in terms of magnetic flux closure between the Py and Co layers for the antiferromagnetic coupling case.

Direct measurement of rotatable and frozen CoO spins in exchange bias system of CoO/Fe/Ag(001)

The exchange bias of epitaxially grown CoO/Fe/Ag(001) was investigated using x-ray magnetic circular dichroism and x-ray magnetic linear dichroism (XMLD) techniques. A direct XMLD measurement on the CoO layer during the Fe magnetization reversal shows that the CoO compensated spins are rotatable at thinner thickness and frozen at larger thickness. By a quantitative determination of the rotatable and frozen CoO spins as a function of the CoO film thickness, we find the remarkable result that the exchange bias is well established before frozen spins are detectable in the CoO film. We further show that the rotatable and frozen CoO spins are uniformly distributed in the CoO film.

Symmetry-breaking induced exchange bias in ferromagnetic Ni-Cu-Co and Ni-Fe-Co sandwiches grown on a vicinal Cu(001) surface

Ferromagnetic Ni-Cu-Co and Ni-Fe-Co sandwiches were grown epitaxially onto a vicinal Cu(001) substrate and investigated using magneto-optical Kerr effect and x-ray magnetic circular dichroism techniques. We find that the atomic steps of the vicinal surface break the magnetic reversal symmetry to induce an exchange bias in the Ni perpendicular magnetic hysteresis loop. The Ni exchange bias direction can be switched by changing the direction of the in-plane Co magnetization. In addition, the exchange bias can be tailored by changing the Cu or Fe spacer layer thickness.

Magnetic bubble domain phase at the spin reorientation transition of ultrathin Fe/Ni/Cu(001) film

Magnetic domain phases of ultrathin Fe/Ni/Cu(001) are studied using photoemission electron microscopy at the spin reorientation transition (SRT). We observe a new magnetic phase of bubble domains within a narrow SRT region after applying a nearly in-plane magnetic field pulse to the sample. By applying the magnetic field pulse along different directions, we find that the bubble domain phase exists only if the magnetic field direction is less than approximately 10 degrees relative to the sample surface. A temperature dependent measurement shows that the bubble domain phase becomes unstable above 370 K.

Spin-dependent quantum interference from epitaxial MgO thin films on Fe(001)

Spin-dependent electron reflection from MgO thin films grown on Fe(001) was measured using spin-polarized low energy electron microscopy. The electron reflectivity exhibits quantum interference from which two MgO energy bands with Delta1 symmetry were determined in experiment. We found that a bulklike MgO energy gap is fully established for MgO film thicker than 3 atomic monolayers and that the electron reflectivity from the MgO/Fe interface exhibits a spin-dependent amplitude and a spin-independent phase change.

Band structure and oscillatory electron-phonon coupling of Pb thin films determined by atomic-layer-resolved quantum-well states

Using a low temperature growth method, we have prepared atomically flat Pb thin films over a wide range of film thickness on a Si-(111)-7 x 7 surface. The Pb film morphology and electronic structure are investigated in situ by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. Well-defined and atomic-layer-resolved quantum-well states of the Pb films are used to determine the band structure and the electron-phonon coupling constant (lambda) of the films. We found an oscillatory behavior of lambda with an oscillation periodicity of two atomic layers. Almost all essential features in the Pb/Si(111) system, such as the growth mode, the oscillatory film stability, and the 9 monolayer envelope beating pattern, can be explained by our results in terms of the electron confinement in Pb films.

Body-centered-cubic Ni and its magnetic properties

The body-centered-cubic (bcc) phase of Ni, which does not exist in nature, has been achieved as a thin film on GaAs(001) at 170 K via molecular beam epitaxy. The bcc Ni is ferromagnetic with a Curie temperature of 456 K and possesses a magnetic moment of 0.52+/-0.08 micro(B)/atom. The cubic magnetocrystalline anisotropy of bcc Ni is determined to be +4.0x10(5) ergs x cm(-3), as opposed to -5.7x10(4) ergs x cm(-3) for the naturally occurring face-centered-cubic (fcc) Ni. This sharp contrast in the magnetic anisotropy is attributed to the different electronic band structures between bcc Ni and fcc Ni, which are determined using angle-resolved photoemission with synchrotron radiation.

Spin-dependent Fabry-Pérot interference from a Cu thin film grown on fcc Co(001)

Spin-dependent electron reflection from a Cu thin film grown on Co/Cu(001) was investigated using spin-polarized low-energy electron microscopy (SPLEEM). Fabry-Pe rot type interference was observed and is explained using the phase accumulation model. SPLEEM images of the Cu overlayer reveal magnetic domains in the Co underlayer, with the domain contrast oscillating with electron energy and Cu film thickness. This behavior is attributed to the spin-dependent electron reflectivity at the Cu/Co interface which leads to spin-dependent Fabry-Pe rot electron interference in the Cu film.

Superconductivity Modulated by Quantum Size Effects

We have fabricated ultrathin lead films on silicon substrates with atomic-scale control of the thickness over a macroscopic area. We observed oscillatory behavior of the superconducting transition temperature when the film thickness was increased by one atomic layer at a time. This oscillating behavior was shown to be a manifestation of the Fabry-Perot interference modes of electron de Broglie waves (quantum well states) in the films, which modulate the electron density of states near the Fermi level and the electron-phonon coupling, which are the two factors that control superconductivity transitions. This result suggests the possibility of modifying superconductivity and other physical properties of a thin film by exploiting well-controlled and thickness-dependent quantum size effects.

Kinetic limitations in electronic growth of Ag films on Fe(100)

Quantum well (QW) resonances are identified in Ag films on an Fe(100) surface and are used in low energy electron microscopy to monitor film morphology during annealing and growth. We find that Ag films thermally decompose to thicknesses that are stabilized by QW states at the Gamma point. Novel growth morphologies are also observed that highlight the competition between kinetic limitations and the QW state energetics that promote electronic growth. These combined observations help to explain the unusual bifurcation mode of thermal decomposition that was reported previously for this system.

Magnetic stripe domains in coupled magnetic sandwiches

Magnetic stripe domains in the spin reorientation transition region are investigated in (Fe/Ni)/Cu(001) and Co/Cu/(Fe/Ni)/Cu(001) using photoemission electron microscopy. For (Fe/Ni)/Cu(001), the stripe domain width decreases exponentially as the Fe/Ni film approaches the spin reorientation transition point. For Co/Cu/(Fe/Ni)/Cu(001), the Fe/Ni stripe orientation is aligned with the Co in-plane magnetization, and the stripe domain width decreases exponentially with increasing the interlayer coupling between the Fe/Ni and Co films. By considering magnetic stripes within an in-plane magnetic field, we reveal a universal dependence of the stripe domain width on the magnetic anisotropy and on the interlayer coupling.

Effect of gene dose and parental origin on bone histomorphometry in X-linked Hyp mice

X-linked hypophosphatemia (XLH) is characterized by rickets and osteomalacia and arises from mutations in the Phex and PHEX genes in mice (Hyp) and humans, respectively. The present study was undertaken to examine the effect of gene dose on the skeletal phenotype using a histomorphometric approach. Metrical traits (vertebral length, growth plate thickness, cancellous osteoid volume per bone volume, and cancellous, endocortical, and periosteal osteoid thickness) were compared in caudal vertebrae of mutant female (Hyp/+, Hyp/Hyp) and male (Hyp/Y) mice and their normal female (+/+) and male (+/Y) littermates. Mutant animals had trait values that differed significantly from those of normal animals. However, with the exception of vertebral length and cancellous osteoid thickness, values were not significantly different between the three mutant genotypes. We also examined the effect of gamete-of-origin on histomorphometric parameters in obligate Hyp/+ females derived from male or female transmitting parents. The metrical trait values in both groups of Hyp/+ mice were similar, with the exception of vertebral length and cancellous osteoid volume per bone volume. In summary, we demonstrate that the amount of osteoid per bone volume is similar in the three mutant genotypes and conclude that the extent and magnitude of the mineralization defect is fully dominant and likely not affected by gene dose. The differences in vertebral length in the mutants suggest that rickets and osteomalacia are not the only causes of decreased vertebral growth in Hyp mice and that Phex protein may influence bone growth and mineralization by distinct pathways.

Magnetic phase transition in Co/Cu/Ni/Cu(100) and Co/Fe/Ni/Cu(100)

Magnetic phase transitions in coupled magnetic sandwiches of Cu/Co/Cu/Ni/Cu(100) and Cu/Co/Fe/Ni/Cu(100) are investigated by photoemission electron microscopy. Element-specific magnetic domains are taken at room temperature to reveal the critical thickness at which the magnetic phase transition occurs. The results show that a coupled magnetic sandwich undergoes three types of magnetic phase transitions depending on the two ferromagnetic films' thickness. A phase diagram is constructed and explained in the process of constructing Monte Carlo simulations, which corroborate the experimental results.

Parental origin of mutant allele does not explain absence of gene dose in X-linked Hyp mice

The expectation for a gene dose effect in an X-linked phenotype is that the corresponding metrical trait in heterozygous females will lie between values for affected hemizygous males and unaffected males and females. We made sequential measurements (at 30, 60, 90, 120 and 150 days) of serum phosphate concentration and tail length in mice with X-linked hypophosphatemia (genotypes: Hyp/Y, Hyp/+ and Hyp/Hyp) and in their normal litter-mates (genotypes: +/Y, +/+). We also measured renal mitochondrial 25-hydroxyvitamin D3-24-hydroxylase (24-hydroxylase) activity in 5 to 7-month-old mice fed control and low phosphate diets and representing all five genotypes. The animals were obtained by controlled breeding under uniform environmental conditions. The mutant animals all had uniformly and significantly lower serum phosphate levels, shorter tail length and higher 24-hydroxylase activity relative to unaffected litter-mates. There was no evidence of a gene dose effect because values were not significantly different among the three mutant genotypes. We also studied the influence of gamete of origin on serum phosphate, tail length and renal mitochondrial 24-hydroxylase activity in the Hyp/+ offspring of affected males (Hyp/Y) or affected females (Hyp/+ or Hyp/Hyp). We found no effect on the distribution of trait values. We conclude that parental origin of mutant allele does not explain the absence of a gene dose effect in Hyp mice.