P.J. Grundy

Deposition of polycrystalline thin films with controlled grain size

Difficulties in controlling the grain size and size distribution in polycrystalline thin films are a major obstacle in achieving efficient performance of thin film devices. In this paper we describe a sputtering technology that allows the control of the grain size and size distribution in sputtered films without the use of seed layers, substrate heating or additives. This is demonstrated for three different materials (Cr, NiFe and FeMn) via transmission electron microscopy imaging and grain size analysis performed using the cumulative percentage method. The mean grain size was controlled only via the sputtering rate. We show that higher sputtering rates promote the growth of larger grains. Similar trends were obtained in the standard deviation, which showed a clear reduction with the sputtering rate.

Electron microscope study of precipitation in a niobium-containing (Nd, Dy)-Fe-B sintered magnet

Abstract The microstructure of a niobium-containing (Nd, Dy)-Fe-B alloy has been investigated using transmission electron microscopy, STEM and SEM X-ray microanalysis and optical microscopy, Magnetic measurements showed an increase in coercivity when niobium was added to a (Nd, Dy)-Fe-B magnet. The microstructure was found to be similar to that of a ternary Nd-Fe-B magnet but with two additional phases, a Laves Fe2Nb compound and a finely dispersed niobium containing coherent precipitate found in the magnetically hard phase. Lorentz microscopy indicated domain wall interactions with the fine precipitates which may be responsible for the enhanced coercivity of the niobium doped magnet.

Magnetostriction in TbDyFe thin films

Magnetization and magnetostriction in amorphous binary TbFe and DyFe and amorphous and polycrystalline, ternary (TbxDy1−x)yFe100−y thin films have been investigated. The measurements reflect the compositional dependence of the easy direction of magnetization in the films. In plane magnetostrictions of over 300×10−6 were measured for some of the amorphous TbFe and TbDyFe films and values greater than 750×10−6 were obtained in polycrystalline TbDyFe films near to the Terfenol composition.

Preparation of high moment CoFe films with controlled grain size and coercivity

In this paper a preparation method for high moment CoFe thin films with soft magnetic properties is reported. A full control of coercivity in a series of 20-nm-thick CoFe films has been achieved without using seed layers, additives, or thermal annealing. The films were sputtered directly onto Si substrates and the coercivity was varied by changing the mean grain size in the sputtered films. The mean grain size was in turn controlled via the sputtering rate. A reduction in the coercivity has been observed from 120Oe for samples with a mean grain size larger than 17nm down to 12Oe for a sample with a mean grain size of 7.2nm. The results are in good agreement with the “random anisotropy model” relating the coercivity to the mean grain size in polycrystalline ferromagnetic films.

Giant magnetoresistance in sputter deposited Co/Cu multilayer systems

This paper presents some results of magnetoresistance measurements on sputter deposited Co/Cu thin film multilayers. We find that large values of magnetoresistance approaching 40% can be obtained and that these values oscillate in magnitude with the thickness of the non-magnetic spacing layer with a period of about 1.1 nm. It appears that the multilayer must be grown on a particular form of underlayer to realize these large values of magnetoresistance ratio.

Novel sputtering technology for grain-size control

In this paper, we present a description of a novel high-rate plasma sputtering system that allows the control of grain size in sputtered films. Additionally, the system has the advantage of a better utilization of the target material (around 80% to 90%) by eliminating the race track at the target as in conventional plasma magnetron sputtering systems. The potential and capabilities of this novel plasma sputtering device are demonstrated in this paper by the deposition of a number of different Cr thin films suitable for underlayers in thin-film media and for which we have performed a systematic X-ray and TEM analysis to determine the grain-size histograms, mean grain diameters, and their relationship to the sputtering processes.

MAGNETOSTRICTION IN POLYCRYSTALLINE SPUTTER-DEPOSITED TBDYFE FILMS

Magnetic and microstructural investigations of some polycrystalline rare‐earth—transition‐metal (RE‐TM) alloy thin films are reported. Emphasis was placed on pseudobinary alloys in the (TbxDy1−x)Fe2 and (TbxDy1−x)3Fe4 systems. The films were prepared by sputter deposition onto both room‐temperature and high‐temperature substrates. Films prepared on room‐temperature substrates were amorphous and were crystallized by postdeposition annealing. Transmission electron microscopy and x‐ray diffraction showed and indicated a complex microstructure consisting of small grains of free iron, REFe compounds, and some RE oxide phases. Magnetization, coercivity, and magnetostriction measurements showed the films to be essentially magnetized in plane with a trend across the composition range which reflected the different influences of Tb and Dy and also the compensation condition. Magnetostriction values greater than 0.75×10−3 were found near the Terfenol composition Tb0.27Dy0.73Fe2 and for x≳0.3.

The magnetic and microstructural properties of Co-Cr thin films with perpendicular anisotropy

Abstract This paper reports measurements of the magnetic properties of dc sputter deposited Co 100− x Cr x alloy thin films for 0 ⩽ x ⩽ 30 at %. Properties of interest are those obtained from the in-plane and perpendicular hysteresis loops such as magnetization, saturation fields and coercivities. These properties are correlated with the microstructure, crystal structure and, to some extent, the magnetic domain structure of the films. For particular preparation conditions and within a certain composition range the films are found to have some of the properties suitable for perpendicular magnetic recording applications, i.e., perpendicular magnetization and high coercivity.

Microstructure of sputter-deposited Co/Si multilayer thin films

This article presents the results of an investigation by transmission electron microscopy, electron diffraction, x-ray diffraction, and x-ray reflectivity of sputter-deposited Co/Si multilayers. Structures with individual layer thicknesses above about 5 nm retain elemental regions and also some interfacial mixing, but below this thickness very significant intermixing occurs with alloy formation through interdiffusion. Changes in composition in these interfacial regions reveal themselves as a change in atomic arrangement from crystalline to amorphous phases. This can be induced either by increasing the Si or reducing the Co layer thickness, resulting in alloy formation over a limited distance with a variable average composition. A simple model is proposed to explain the observed microstructural changes.

Magnetic and magnetostrictive properties of amorphous rare earth-transition metal alloy films

The magnetic and magnetostrictive properties of amorphous binary TbxFe100-x and DyxFe100-x and amorphous ternary (TbxDy1-x)20Fe80, (TbxDy1-x)33Fe67 and (TbxDy1-x)43Fe57 thin films are presented. The films were prepared by sputter deposition from composite targets onto nominally room temperature substrates. Magnetization, coercivity and magnetostriction measurements reflect the compositional dependence of the easy direction of magnetization in the films. In-plane magnetostrictions of over 300*10-6 were measured for some of the TbxFe100-x and (TbxDy1-x)43Fe57 films.