Direct ferromagnetic antiferromagnetic exchange biasing energy is determined by small reversible rotations of the magnetization away from the unidirectional easy axis using an externally applied magnetic field. The angle the magnetization makes relative to the easy direction is determined by measuring the anisotropic magnetoresistance. This technique gives energies larger by a factor of 2 than the traditional measurements of the shift in the hysteresis loop (an irreversible process) of the ferromagnetic layer in bilayer samples of Co/CoO. An apparent Co thickness variation of the experimentally determined exchange biasing interface energy indicates the Co magnetization is not uniform but probably spirals through the thickness of the film.

In the emerging field of spin-electronics ideal ferromagnetic electron sources would not only possess a high degree of spin polarization, but would also offer control over the magnitude of this polarization. We demonstrate here that a simple scheme can be utilized to control both the magnitude and the sign of the spin polarization of ferromagnetic CoS2, which we probe with a variety of techniques. The position of the Fermi level is fine-tuned by solid solution alloying with the isostructural diamagnetic semiconductor FeS2, leading to tunable spin polarization of up to 85%.

A magnetic force microscope �MFM� was used to image topography and magnetic forces from a chain of submicron single magnetic domain particles produced by and contained in isolated magnetotactic bacteria. The noncontact magnetic force microscope data were used to determine a value for the magnetic moment of an individual bacterial cell, of order 10 �13 emu, consistent with the average magnetic moment of bacteria from the same sample, obtained by superconducting quantum interference device magnetometry. The results represent the most sensitive quantification of a magnetic force microscope image to date. © 1995 American Institute of Physics.Magnetic force microscopes have been used for high magnetotactic bacterial strain MV-1 were grown and har resolution imaging of a variety of samples of interest in mivested as previously described. 3 Cells were fixed with 1% cromagnetism. However, the potential of MFMs has yet to be gluteraldehyde and freeze dried. The freeze drying process realized because of the difficulty of quantifying the magnetic insured the magnetosomes were close to the surface of the field the MFM measures. Some progress towards quantificacell, simplifying the magnetic imaging. The freeze-dried tion has occurred, 1 but has been limited primarily by the cells had a coercivity of 385 Oe at room temperature. Indi uncertainties in the micromagnetics of the specimens. As a vidual magnetite particles in strain MV1 are truncated hexa step towards overcoming this limitation, we have quantified hedral prisms with average dimensions of 53�35�35 nm the response of a MFM to a simple micromagnetic system and organized in a single linear chain of 10-25 particles. 4 consisting of a linear chain of single magnetic domain parUsing a SQUID magnetometer, 5 the average moment per ticles within a magnetotactic bacterium. The geometrical bacterium was determined to be 1.6�10 �13 emu at 300 K simplicity of the particle chain facilitates the quantification agreeing with previous measurements of the moments of process because it was possible to estimate the total magnetic magnetotactic bacteria. 1,6 dipole moment of the chain assembly by simply measuring To correlate the magnetic field measurement with an inthe chain length. This estimate provided the starting point for dividual cell, it was necessary to obtain the topographic and a nonlinear model of the MFM image. The fitted moment associated magnetic images of the magnetotactic bacterium resulting from the nonlinear model agreed well with the av with the same cantilever. A Nanoscope III from Digital In erage moment estimated from magnetic measurements on a struments was used in the ''tapping mode'' 7 to get a topo bulk sample of the bacteria.graphic image of the cell. The cantilever was then retracted Magnetotactic bacteria mineralize intracellular magnetofrom the surface and a noncontact magnetic force mode im somes, which are membrane-enclosed, single-magnetic 2 age was taken over the same area of the sample. This process domain particles of magnetite, Fe 3 O 4 , or greigi...

Oscillations in the exchange coupling between ferromagnetic La 2/3 Ba 1/3 M nO3 layers with paramagnetic LaN iO3 spacer layer thickness has been observed in epitaxial heterostructures of the two oxides. This behavior is explained within the RKKY model employing an ab initio calculated band structure of LaN iO3, taking into account strong electron scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a positive current-in-plane magnetoresistance. 75.70.Cn, 75.30.Vn, 71.18.+y, 75.70.Pa Since the discovery of giant magnetoresistance [1] and oscillatory interlayer coupling [2], metallic magnetic multilayers have been the subject of intensive research [3]. A physical picture of the coupling is provided in terms of quantum interference due to confinement of electrons in the nonmagnetic spacers [4,5]. Ruderman-KittelKasuya-Yosida (RKKY) theory [6], successfully used to describe the effect, appears to be a limiting case of a more general approach [5]. The prediction that oscillations periods are determined by the extremal spanning vectors of the Fermi surface of the nonmagnetic spacer is now supported by a wealth of experimental data [7]. The phase and magnitude of the coupling oscillations apparently are sensitive to the interface matching of the electron bands for a particular magnetic configuration of the layers [3][4][5].While these effects have been studied in many simple metal and alloy systems, little progress has been achieved in investigating them in multilayers consisting entirely of compounds [8]. In this Letter we report the first observation of oscillatory coupling in heterostructures fabricated entirely of oxides, thus extending the field to a novel class of materials. The ferromagnetic layer material, barium-doped lanthanum manganese oxide La 2/3 Ba 1/3 M nO 3 belongs to the family of metallic manganese oxides that exhibit very large (colossal) magnetoresistance [9]. Double exchange ferromagnetism [10] predicts half-metallicity in these compounds, which has been justified by ab initio band structure calculations [11] as well as confirmed (to a certain degree) experimentally [12]. As a spacer layer material, we have employed LaN iO 3 , which is lattice-matched to La 2/3 Ba 1/3 M nO 3 , and is the only rare earth nickelate that is a paramagnetic metal [13]. Its susceptibility is strongly enhanced by electron-electron exchange interactions [14]. In thin film form, it is a better conductor (resistivity of 50 − 100 µΩ · cm) than the manganites (resistivity of 300 − 500 µΩ · cm). Although advances in oxide film growth permit the fabrication of atomically defined layered structures with nanometer scale periodicity [15], the very strict control over stoichiometry and deposition conditions required to produce multilayers remains a significant experimental challenge.In our previous paper [16] we presented the evidence for antiferromagnetic (AFM) interlayer coupling in this system. Here we demonstrate that the initially AFM coupling becomes ferromagnetic (FM) at larger spacer thicknesses a...

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