Peter Lubitz

Bio: Peter Lubitz is an academic researcher from United States Naval Research Laboratory. The author has contributed to research in topics: Ferromagnetic resonance & Magnetic anisotropy. The author has an hindex of 21, co-authored 65 publications receiving 1299 citations.

CoFe2O4 thin films grown on (100) MgO substrates using pulsed laser deposition

Abstract: Thin films (≊04 μm) of cobalt ferrite (CoFe2O4) have been grown on single‐crystal (100) MgO substrates using pulsed laser deposition (PLD) The phase, orientation, and microstructure of the as‐deposited films were investigated as a function of substrate temperature (ie, 200–800 °C) at a constant oxygen deposition pressure of 30 mTorr The as‐deposited films were found to be single phase, well oriented, and approximately matching the stoichiometry of the target, but the cubic lattice constant of the films depended on the substrate temperature indicating that the films were strained The greatest effect of the substrate temperature was on the magnetic properties of the as‐deposited films At 800 °C, 4πMs was measured to be 5370 G which is approximately the accepted bulk value for cobalt ferrite In addition, PLD cobalt ferrite films grown at substrate temperatures of 600 and 800 °C exhibited a uniaxial magnetic anisotropy with an easy direction normal to the film plane Films grown at 200 and 400 °C also

The magnetic and structural properties of pulsed laser deposited epitaxial MnZn–ferrite films

Abstract: The magnetic and structural properties of pulsed laser deposited MnZn–ferrite films have been examined. The results show that the uniaxial anisotropy, ferromagnetic resonance linewidth and coercive force are strongly influenced by the microstructure of the films, and the saturation magnetization and first‐order magnetocrystalline anisotropy constant depend on intrinsic properties such as composition and cation site occupation. A comparison of bulk and film magnetic properties shows that the magnetic properties of the films are comparable to the bulk, which makes pulsed laser deposition ferrite films a prime candidate for thin film high‐frequency microwave device applications.

Pulsed laser deposition of epitaxial BaFe12O19 thin films

Abstract: Epitaxial thin films of barium hexaferrite (BaFe12O19) have been fabricated by the pulsed laser deposition technique on basal plane sapphire. Structural studies reveal the films to be predominantly single phase and crystalline, with the c axis oriented perpendicular to the film plane. The magnetic parameters deduced from vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are close to the parameters associated with bulk materials. Post annealing of the films reduced the FMR linewidth by more than a factor of 3 so that it compares reasonably well with single‐crystal films. The derivative FMR linewidth was measured to be 66 Oe at 58 GHz and 54 Oe at 86 GHz. Spin‐wave‐like modes have been observed for the first time in barium ferrite films. The deduced exchange stiffness constant of 0.5×10−6 ergs/cm is in reasonable agreement with recent calculations.

Ferromagnetic resonance studies of very thin epitaxial single crystals of iron

Abstract: Ferromagnetic resonance (FMR) has been used to study a wide variety of very thin single crystals of Fe grown on (110) GaAs substrates by molecular beam epitaxy. Data were taken at room and liquid nitrogen temperatures for films with thicknesses L in the range 18–200 A. Due to surface anisotropy, the easy axis of the magnetization switches from [100] to [110] when L≤50 A, independent of whether the the film surface is passivated by an Al‐overcoat or has a thin Fe oxide surface layer. We suggest that this is an effective surface anisotropy arising in part from a depth dependent strain near the film‐substrate interface. The changes in the parameters describing the angular dependence of the FMR spectra upon cooling to 77 K can be explained as due to magnetostriction arising from thermally induced strains plus the temperature dependence of the cubic volume anisotropy. The FMR linewidth is shown to be a linear function of frequency in the range 5–40 GHz.

Observation of magnetic resonance modes of Fe layers coupled via intervening Cr (invited)

Abstract: Multiple‐frequency (2–14 GHz) ferromagnetic resonance (FMR) has been used to directly observe the coupled resonance modes of a large set of single‐crystal Fe/Cr/Fe(001) sandwiches grown by molecular‐beam epitaxy The FMR data reveal two resonance modes which have complicated frequency dependencies for those samples that show antialigned Fe layers in zero applied field Such alignment is only found for samples with 12 A

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Nonlocal magnetization dynamics in ferromagnetic heterostructures

Abstract: Two complementary effects modify the GHz magnetization dynamics of nanoscale heterostructures of ferromagnetic and normal materials relative to those of the isolated magnetic constituents. On the one hand, a time-dependent ferromagnetic magnetization pumps a spin angular-momentum flow into adjacent materials and, on the other hand, spin angular momentum is transferred between ferromagnets by an applied bias, causing mutual torques on the magnetizations. These phenomena are manifestly nonlocal: they are governed by the entire spin-coherent region that is limited in size by spin-flip relaxation processes. This review presents recent progress in understanding the magnetization dynamics in ferromagnetic heterostructures from first principles, focusing on the role of spin pumping in layered structures. The main body of the theory is semiclassical and based on a mean-field Stoner or spin-density-functional picture, but quantum-size effects and the role of electron-electron correlations are also discussed. A growing number of experiments support the theoretical predictions. The formalism should be useful for understanding the physics and for engineering the characteristics of small devices such as magnetic random-access memory elements.

Mechanisms for exchange bias

Abstract: Modern applications for thin film magnets involve unique requirements for the control and design of specific magnetic properties. The exchange bias effect in ferromagnet/antiferromagnet bilayers appears to be a useful feature for controlling one of the most important characteristics of a ferromagnet: coercivity. Prospects for control and enhancement of desirable effects depend upon a clear understanding of mechanisms governing exchange bias. The processes underlying the existence and properties of exchange bias are reviewed, with particular emphasis on the roles of interface structure and temperature. Results from numerical simulations are used to illustrate how exchange bias is modified by geometric structures at the interface and randomly placed defects. A general theoretical formulation of the bias problem is proposed, and an expression for the interface energy is derived. A key result is the existence of higher-order coupling terms when more than one sublattice of the antiferromagnet is present at the interface. Results from calculations of finite temperature effects on bias and coercivity are described, and the concept of viscosity in the antiferromagnet is discussed. A brief discussion is also included of how a dynamic linear response, such as ferromagnetic resonance or light scattering, can be used to determine relevant anisotropy and exchange parameters.