Many times this affects the physical properties of the materials, and there are often many discrepancies in the results described in the literature (Gasgnier, 1980). In the case of binary or ternary rare earth systems as thin films, which are either amorphous (alloys) or crystalline (composites), the problems of preparation, characterization, crystallization (and/or recrystallization) and above all of determination. of basic physico-chemical laws, are acute.
Rare earth-transition metal systems
Ternary amorphous alloys
For GdxNil_x alloys, it is concluded that the sign of the Hall resistivity for Ni is negative (McGuire et al., 1977). They conclude that the inhomogeneities are randomly distributed throughout the film volume.
Crystalline compounds
1975a) observed a faster decrease in magnetization for GdNi than for SmNi—it reaches zero at ~ 16 at% Gd; the magnetostriction of GdNi is lower than that of GdFe and GdCo and rapidly decreases to zero by 32 at%. 1974), with simultaneous thermal evaporation (tungsten crucibles), studied the formation of various compounds in GdNi films deposited at 470 K and heated at 720 K. They observed, depending on the Gd content, the presence of several phases, such as Gd2Ni17, GdNi4, Gd2NiT, GdNi3, GdNi2 and GdNi. Compared to additions of Cu or Au, for which increases were found (see Sections 3.1 and 3.3), they suggest that the differences are due to chemical bonding: Cu and Au are insoluble in Co, while Mo forms many compounds with Co. 1978) showed changes in Ms and Ku with annealing time at a temperature of 500 K and for different Mo contents.
Ternary alloys
- Gadolinium-cobalt-molydenum films
- Gadolinium-cobalt-gold films
Heiman and Kazama (1978), regarding terbium, noted a reduction of the magnetization of DyCu and HoCu samples. In the later paper, the authors conclude that alloys with Nd, Gd, Tb, Dy and Ho are ferromagnetic at 4.2 K, with a Curie temperature below 25 K, except for Gd, for which it is close to 77 K . The magnetization is one-third to one-half of the expected saturation, except again for Gd. However, their results are interesting because they observe a very high coercive force of 30,000 Oe (12,000 for the bulk) for a thin film (4000 A) deposited on glass substrates heated to 770 K. They attribute this large value to the magnetic anisotropy and to the fine-grained structure. 1976), for (Sm, Gd)Cos_xCux films prepared by flash evaporation on substrates heated to 470 K, observed large magnetic aftereffects.
The authors believe that E P R is promising for studying the electric field gradients (or crystal fields) in amorphous rare earth alloys (see next section for transport properties). 1980) have observed in (Gd, Dy or Er)50Ags0 an increase in the resistivity at low temperature and a negative magnetoresistance. They discuss their results in terms of the sticking effect, the nature of the substrates (quartz or NaCl) inducing deformation, and cracking or sliding effects.
In the vicinity of Tcomp (285 K), the dependence of He was determined. 1978) studied the dependence of the domain wall velocity on the presence of an interlayered permaloy film, temperature and driving field.
Rare earth-bismuth and tin systems
The authors conclude that a strong reduction o3 the exchange constants and a stronger localization of the Fe spin occurs. Upon aging at ambient atmosphere, or annealing in air at 370 K, the formation of a compound identified as Sm(OH)a is observed (see fig. 10). This compound is identified by comparison with the known patterns of the light rare earth hydroxides (Gasgnier, 1980).
RE-ALLOY AND COMPOUNDS AS THIN FILMS 75 microscope, in the first stage of heating the SmBi films while forming a C-Sm2 O3 film, the bismuth is simultaneously volatilized as it coalesces into droplets. Annealing in air at 470 to 720 K produces C-Gd203, and at the same time there is the appearance and disappearance of different phases. During annealing of the thinner Bi films with the electron beam, the formation of C- and B-Gd203 takes place.
These droplets are believed to be Bi, as there is no formation of GdBi compounds or Bi oxides.
Rare earth-aluminum systems 1. Amorphous state
By slowly changing the condenser opening, it is possible to gradually heat the sample. The indexing of the electron diffraction patterns shows that the small and large crystals are DyA13. The difference between the two values leads to a slight distortion of the ideal stacking sequence.
The small crystallites obtained after annealing the thin amorphous films have a primitive cubic lattice. They take the form of thin lamellae, for which the c-axis of the stacking planes is parallel to the electron beam. Briefly, the crystals generally have either a hexagonal compact cell (denoted as nlH) or a rhombohedral cell (denoted as n2R, where n2 is an integer of 3). The stacking sequence notation is abbreviated with Ramsdell notation.) Each is characterized by the presence (hexagonal structures) or absence (rhombohedral structures) of the (10.0) reflection.
They are characterized either by small crystallites in the first stage of heating or by large crystals in the last stage.
Superconducting systems
Some spot systems are characterized as row spots but cannot be indexed according to the polytype structures of the RAI3 compounds. From their resistivity and magnetic susceptibility measurements, they discuss the formation of ErA1 compounds at 300 K. They observed the total dissociation of A1203 and the appearance of the following compounds: ERA1, ErA12, ERA13 and ErEA13. and high frequency electromagnetic experiments. The samples show changes in the transition temperature and the Kondo resistance upon annealing at 77 and 20 K, respectively.
The critical current and clamping force density curves show the highest critical current density achieved for B = 0 a n d T = l. During annealing, several diffraction peaks appear and disappear, which could not be attributed to any of the known SmMg or MgH2 compounds. At the same time, new crystals appear, which cannot be indexed as any of the known compounds SmMg, SmH2, MgH: or C-Sm2O3.
He reported the dependence of the spontaneous Hall effect and the magnetoresistance on the applied field.
Rare earth-chalcogenide systems
They found that the optical absorption can be explained by the characteristics of the electronic structure of Sm 2+ ions and. RE ALLOYS AND COMPOUNDS AS THIN LAYERS 93 interaction of the 4f and 5d states with the crystal field environment. Such parameters can cause strong changes in the optical, magnetic and electrical properties of the film.
1979) have studied the dependence of the absorption spectra on the nature and temperature of the substrate, impurities and lattice effects. Ahn and Shafer (1971) noted low electrical resistance in Eu excess films. 1979) showed that the nature of the substrate can change the resistivity, e.g. Ahn and Shafer (1971) have observed that the switching properties in their films are similar to those of the stoichiometric samples.
Vasilkovskii et al (1977) studied Er2Te3 thin films deposited by thermal evaporation on a hot substrate (up to 370 K).
Rare earth-pnictide systems
They have shown by electron microscopy the influence of yttrium concentration on the formation of A-, B- and C-type Nd203, and the epitaxy between them. The composition of the deposited film varies with HES pressure, e.g. in the case of the La-S system the following phases were identified:. After electron microscope electron beam heating, the thinnest films of lanthanum of the two sequences show the formation of C- and B-Sm203 and A-La203.
The two points near the central point do not correspond to the B-Gd203 structure. RE ALLOYS AND COMPOUNDS AS THIN FILMS 105 sequences show, without annealing, the coexistence of C - 8 m 2 0 3 and LaH2 structures. With further annealing, new crystals appear, but the electron diffraction patterns do not match the known structures. Therefore, some physical, chemical and crystallographic properties and other phenomena are difficult to explain.
This naturally leads to the problem of the reproducibility of the samples, and also has a great influence on the industrial applications.
GRATZ
Transport properties of non-magnetic rare earth intermetallic compounds 1. Theoretical introduction
- Electrical resistivity
However, in some metals, the introduction of impurities causes an increase in the magnitude of the thermopower at low temperature. The electronic component can be written as follows in terms of the thermal resistance W of the electronic system. Allen (1980) points out that the maximum resistivity for d-band compounds and alloys is on the order of 150 ixl~ cm.
2 shows the temperature dependence of resistivity for some transition metal compounds ce- (Van Daal and Buschow, 1970). The discrepancy can be understood in terms of the theory proposed by Kelly and McDonald (1952). Therefore, the anomalies in the resistance behavior can be understood by a dramatic change of the phonon spectrum at this transition.
As discussed in Section 2.1.3, the thermal conductivity of a metal consists of two contributions, namely an electronic part and a lattice part. )re is usually assumed to make a small contribution to the total conductivity for pure metals (Ziman, 1960).
Transport properties of rare earth-non-transition-metal compounds exhibiting long-range magnetic order
This contribution, Pmag, describes scattering processes of conduction electrons due to disorder in the arrangement of the magnetic moments. An increase in the magnitude of the magnetic moment will result in an increase in Sin. The thermopower of the following RI compounds was compared: YA12 and GdA12 (MgCu2 structure), YCu2 and GdCt12 (CeCu2 structure), and LaNi and GdNi (orthorhombic CrB structure).
The temperature dependence of the resistance of heavy compounds RAlz (R = Gd, Tb, Dy, Ho, Er, Tm) is shown in fig. Inset shows resistivity behavior near the Jahn-Teller transition temperature in PrCu2 (Sassik and Gratz, 1981). The T curve of HoCu2 in the vicinity of the Ne61 temperature TN and ordering to order the transition temperature Ts (6.5 K).
No sharp kink at TN is observable in the resistivity of the antiferromagnetically ordered samples of the Tb(Ni, Cu)2 system.
GRATZ AND M.J. ZUCKERMANN
Transport properties of rare earth-transition metal compounds exhibiting itinerant magnetism
The SCR theory was then used to analyze the temperature dependence of the resistivity o(T) for weak ferromagnets. The temperature variation of the resistivity due to magnetic cattering (pm) in Y(Col-xFex)2 (Ikeda, 1977b). The cause of the minimum in the resistance curves in the intermediate concentration range is unknown.
Susceptibility and NMR measurements show that only some of the Co atoms are magnetic (Figiel et al., 1980). The field dependence of the magnetization of Y4Co3 near the superconducting transition temperature (Gratz et al., 1981b). This instability can be detected by having a discontinuity in the residual resistivity as a function of Co co co n c e n t r a t i o n (Fig. 72).
The temperature dependence of the resistance of two pseudobinary series R6(Fe, Mn)23 is shown in fig.
