High Gd Concentrations Research Articles

Evaluating the role of zinc in the occurrence of fibrosis of the skin: A preclinical study

To investigate the possible role of Zn as a trigger for NSF we were using a previously established preclinical model. The depletion of endogenous Zinc ions (Zn) caused by the administration of gadolinium-based contrast agents (GBCAs) has been suggested as a possible pathomechanism for nephrogenic systemic fibrosis (NSF). In the Zn supplementation study, rats were injected with Gadodiamide, Omniscan, and Magnevist with or without Zn supplementation. In the Zn depletion study, animals were kept on a Zn-deficient diet or a special control diet and received injections of Omniscan, OptiMARK, Magnevist, Gadovist, and Gd-EDTA. Gd, Zn, and Cu concentrations in tissue were measured and histology of the skin was performed. As seen in earlier studies, a difference in Gd concentration in the skin was observed following treatment with the different GBCAs. High Gd concentration in the skin correlated with the occurrence of NSF-like skin lesions. We observed no differences in the occurrence of skin lesions between the Zn supplementation and the Zn-deficient groups compared to their respective control groups. We found no significant effect of Zn on the initiation of NSF-like skin lesions. The results further support data from previous studies highlighting the importance of complex stability of the investigated GBCAs.

Impact of Renal Impairment on Long-Term Retention of Gadolinium in the Rodent Skin Following the Administration of Gadolinium-Based Contrast Agents

Several publications have suggested a possible association between Gd-based contrast agents (GBCAs) and the development of nephrogenic systemic fibrosis, a rare but serious disease. To date, nephrogenic systemic fibrosis has been observed only in patients with severe renal insufficiency.The aim of this study was to determine the impact of a prolonged circulation time of GBCAs caused by reduced renal clearance on the long-term retention of Gd in the skin of rats after administration of different GBCAs. Renally impaired Han Wistar Rats (5/6-nephrectomized rats) were injected with Omniscan, OptiMARK, Magnevist, or Gadovist. The contrast agents were administered once daily for 5 consecutive days into the tail vein at a dose of 2.5 mmol Gd/kg b.w. Skin biopsies were taken at various time points, and the gadolinium (Gd) concentration was determined by inductive coupled plasma mass spectrometry (ICP-MS) over an observation period of 168 days post injection (p.i.). Differences in the skin Gd concentrations were observed between the 4 investigated GBCAs. For the nonionic linear compounds, Omniscan and OptiMARK, high Gd concentrations were maintained in the skin over the observation period of up to 168 days p.i. For the ionic linear compound, Magnevist, comparatively lower Gd retention in the skin was observed over time. For the macrocyclic compound, Gadovist, the Gd values in the skin were even lower, and significantly lower than Gd values in the skin in Omniscan and OptiMARK treated animals. The results of this preclinical study support the use of 5/6-nephrectomized rats as a model for prolonged circulation time of GBCAs as seen in patients with severe renal impairment. Surgically induced severe renal impairment resulted in delayed clearance of the administered GBCAs in the study animals. The highest amount of Gd was observed in the skin after treatment with the nonionic linear GBCAs, whereas the lowest Gd values were observed after treatment with the macrocyclic agent. This suggests that the difference in the Gd values observed in rat skin tissue after treatment with the different GBCAs is caused of a different propensity of the different GBCAs to release Gd in vivo. However, the analytical method used does not distinguish between chelated and unchelated Gd.

Preclinical investigation to compare different gadolinium-based contrast agents regarding their propensity to release gadolinium in vivo and to trigger nephrogenic systemic fibrosis-like lesions

Recent reports suggest that nephrogenic systemic fibrosis (NSF) is associated with the administration of gadolinium (Gd)-based contrast agents (GBCAs) and in particular with the stability of the Gd-complex. The aim of this investigation was to compare GBCAs and their potential to trigger NSF. Forty-two healthy male rats received repeated intravenous injections of six different GBCAs at high doses to simulate the exposure seen in patients with severe renal dysfunction. Histopathological and immunohistochemical analysis of the skin was performed, and the concentrations of Gd, zinc and copper were measured in several tissues by inductive coupled plasma atomic emission spectroscopy. Macroscopic and histological skin changes similar to those seen in NSF patients were only observed in rats receiving Omniscan. In addition, very high concentrations of Gd were observed in the animals treated with Omniscan, and, to a lesser extent, in animals treated with OptiMARK. Significantly lower levels of Gd were found after the treatment with ionic linear agents and even less after the treatment with macrocyclic agents. The data in this investigation strongly suggest that the stability of the Gd-complex is a key factor for the development of NSF-like symptoms in this experimental setting.

Magnetism in Gd–W films

Vapor condensation techniques are useful to prepare magnetic alloys whose components have low or even negligible equilibrium mutual solubility. In this work, one of these techniques—sputtering—was used to obtain GdxW1−x alloys whose magnetic properties were investigated as a function of the Gd atomic concentration x. Gadolinium and various Gd-based alloys are promising materials for magnetic refrigeration and this was one of the motivations for this study. The Gdx–W1−x films were sputter deposited from Gd and W targets with x ranging from 0 to 1 as determined by x-ray energy-dispersive spectroscopic analyses. X-ray diffraction patterns indicate that crystalline structures were formed at low and high Gd concentrations, while at intermediate concentrations, the films were amorphous. Magnetization measurements, performed as a function of temperature and with static and alternating applied fields, reveal a spin glasslike behavior in all the W-containing samples for temperatures below the freezing temperature Tf. For low and intermediate Gd concentrations, and for T>Tf, the films were paramagnetic, while a ferromagnetic phase was observed in the Gd–W alloy of the highest Gd content. The magnetocaloric effect was investigated from the magnetization isotherms M versus H, from which the isothermal magnetic entropy variation ΔSM as a function of T, for the removal of an applied field of 50kOe, was determined. It was observed that the maximum value of ΔSM for each ΔSM versus T curve and the temperature at which these maxima occur, are strongly dependent on x.

Large magnetization in high Gd concentration GaGdN and Si-doped GaGdN grown at low temperatures

GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular-beam epitaxy on sapphire substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained. X-ray diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth at low temperatures. Local structure around the Gd atom was investigated by extended x-ray absorption fine structure measurement using GdLIII edge. It was shown that Gd atoms were mainly incorporated into the Ga sites in the GaGdN layers. All the samples grown at low temperatures exhibited ferromagnetic characteristics. It is considerable that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism occurs in the low-temperature-grown GaGdN. Furthermore, Si was doped into GaGdN layers during growth in order to increase carrier density, and larger magnetization was observed.

On the magnetic properties of Gd implanted GaN

The wurzite type gallium nitride doped by gadolinium, Ga1−xGdxN (x∼0.01–0.07), was prepared by Gd ion implantation of the parent GaN thin films deposited on sapphire substrates. The material obtained exhibits a weak ferromagnetism (FM) persisting up to 700K. At higher Gd concentrations, the minute FM component coexists with much more pronounced Curie-type paramagnetism. In a dilute limit (x⩽0.01), the latter part is substantially reduced and the saturated FM moment reaches the value M∼2μB∕Gd atom.

A Preclinical Study to Investigate the Development of Nephrogenic Systemic Fibrosis: A Possible Role for Gadolinium-Based Contrast Media

Several recent publications have suggested an association between the administration of gadolinium (Gd)-based contrast agents and the occurrence of Nephrogenic Systemic Fibrosis (NSF), an acquired disorder marked by skin thickening and fibrosis occurring in patients with severe renal dysfunction. The aim of this study was to establish a preclinical experimental setting to investigate the possible link between NSF and Gd-based contrast agents, and specifically the role of Gd and/or depletion of endogenous metal ions as possible triggers for NSF. Thirty-five healthy male rats received repeated intravenous injections of Magnevist (gadopentetate dimeglumine; Gd-DTPA), Omniscan (gadodiamide; Gd-DTPA-BMA), or gadodiamide without caldiamide at a dose of 2.5 mmol Gd/kg body weight over at least 20 days to simulate the exposure to Gd-containing contrast agents in patients with severe renal dysfunction. In addition, caldiamide (the excess ligand in Omniscan) and Gd-ethylenediamine tetraacetic acid (Gd-EDTA) as a positive control, and saline as a negative control were studied. Histopathologic and immunohistochemical analysis of the skin was performed. Gd and zinc concentrations were measured in skin, femur, and liver tissue by atomic emission spectrometry. Rats receiving Gd-EDTA, gadodiamide without caldiamide, and Omniscan developed epidermal ulceration and acanthosis, dermo-epidermal clefts, minimal-to-slight dermal fibrosis, and increased dermal infiltration of different cells, partly positive for CD34 fibrocytes. No such NSF-like macroscopic lesions were observed in the saline, caldiamide, and Magnevist groups. High Gd concentrations in the skin were found in the Gd-EDTA, gadodiamide without caldiamide, and Omniscan groups. In the Magnevist group, Gd levels in the skin were 10-times lower than in the Omniscan-treated animals but elevated compared with saline. A preclinical experimental setting has been established where NSF-like lesions could be observed. The link between the application of Gd-based contrast media and the induction of NSF-like lesions was established. The data indicate that the observed skin lesions are related to the release of Gd and not to the depletion of endogenous ions. The investigations further suggest potential importance of the stability of Gd-based contrast agents.

Variable echo time imaging: Signal characteristics of 1‐M gadobutrol contrast agent at 1.5 and 3T

Gadobutrol (Gd-Bt; Gadovist(R), Schering AG) is a 1-M Gadolinium (Gd)-based contrast agent. Its higher Gd concentration allows for reduction of injection volumes in first pass contrast-enhanced MR angiography (CE-MRA) and should increase bolus sharpness and image quality. However, ambivalent results were reported. In order to explore the performance of 1-M contrast agents such as Gd-Bt and its dependence on molecular environment and temperature, signal characteristics were analyzed for a series of increasing Gd-Bt concentrations for different temperature-controlled samples in water and human blood plasma. Relaxation times, relaxivities, and signal-concentration curves were assessed for several Gd-Bt concentrations in water at 20 degrees C and 37 degrees C and in plasma at 37 degrees C for 1.5T and 3T. Gd-Bt concentration influence on signal intensity (SI) could be effectively simulated and compared with experimental measurements as well as simulations with other contrast agents at realistic in vivo concentrations. Particular attention was given to T(2)- and T(*) (2)-induced losses at high concentrations, which annihilate benefits from T(1) shortening. Based on these findings, variable echo time (VTE) approaches with readout bandwidth varying with k-space position were explored in order to enhance the signal to noise performance of gradient echo imaging at high contrast agent concentrations. Results indicate the potential of VTE for imaging with increased SNR at high contrast agent concentrations.

High Gd Concentration GaGdN Grown at Low Temperatures

GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism occurs in the low-temperature-growth GaGdN.

Molecular MR Imaging of Human Thrombi in a Swine Model of Pulmonary Embolism Using a Fibrin-Specific Contrast Agent

Molecular targeted MR imaging of human clots material in a model of pulmonary embolism using a fibrin-specific magnetic resonance imaging contrast agent (EP-2104R, EPIX Pharmaceuticals, Cambridge, MA). Fresh ex vivo engineered thrombi (human blood) and human clots removed from patients were delivered in 11 swine. Molecular MR imaging with a 3D gradient-echo [3D fast field echo (3DFFE)] sequence and a navigator-gated and cardiac-triggered 3D inversion-recovery black-blood gradient-echo sequence (IR) was performed before thrombus delivery, after thrombus delivery but before contrast media application, and 2 hours after i.v. administration of 4 micromol/kg EP-2104R. MR images were analyzed by 2 investigators and contrast-to-noise ratio (CNR) was assessed. Thrombi were removed for assessment of gadolinium (Gd) concentration. Only after contrast media application were pulmonary emboli [freshly engineered thrombi (n = 23) and human clot material removed from patients (n = 25)] visualized as white foci on MR images. CNR was 13 +/- 3 (ex vivo engineered clot) and 22 +/- 9 (patient clot material) for the fast field echo (FFE)-sequence and 29 +/- 9 (ex vivo engineered clot) and 43 +/- 18 (patient clot material) for the IR-sequence, respectively. A high Gd concentration in the clots was found (82 +/- 43 microM for the freshly engineered and 247 +/- 44 microM for the clots removed from patients, respectively). EP-2104R allows for molecular MR imaging of human clot material in the pulmonary vessels of a swine model.

Long‐term retention of gadolinium in tissues from nephrogenic systemic fibrosis patient after multiple gadolinium‐enhanced MRI scans: case report and implications

Nephrogenic systemic fibrosis (NSF) is a painful and debilitating fibrosing disorder of the skin and systemic tissues. It is associated with exposure to Gd, used in MRIs and MRAs, in patients with renal insufficiency. We here present an illustrative example of a young patient who underwent multiple Gd-enhanced scans, both before and after developing severe NSF. We examined biopsy tissues for quantification of detectable insoluble Gd deposits using automated scanning electron microscopy/energy dispersive X-ray spectroscopy. High concentrations of Gd associated with calcium and phosphorus in skin persisted even 3 years after the last exposure to Gd. Such long-term retention of Gd raises further concerns about the utility and safety of Gd-based contrast agents. Residual Gd chelates, after initial and rapid renal clearance, can dissociate into insoluble, toxic Gd(3+) that precipitates with tissue anions. Bone serves as a site for Gd storage. Subsequent clearance and mobilization from such stores may explain the variable latency of onset of NSF. We hypothesize that long-term persistence and slow release of Gd(3+) from bone stores can be a cause for concern of Gd-associated toxicity with long latency.

Folate-poly-L-lysine-Gd-DTPA as MR contrast agent for tumor imaging via folate receptor-targeted delivery

To study folate-conjugated Gd-DTPA-Poly-L-Lysine (folate-PL-Gd-DTPA) as MR targeting agent to tumor cells via folate receptor, to evaluate feasibility and effectiveness by observing MR signal variations and imaging feature of pulmonary tumor xenografts in nude mice using this contrast material. (1) Using Poly-L-Lysine (PL) as linker, after PL was tethered with caDTPA, GdCl(3) was added to label DTPA-PL, then PL-Gd-DTPA was conjugated to folate, a specific MR contrast agent, was thus prepared. (2) Using high performance liquid chromatography (HPLC) to evaluate the conjugate purity, and the ICP-AES to test Gd(3+) concentration, while the activity evaluated by competitive folate receptor binding with folic acid. (3) Folate-PL-Gd-DTPA as specific contrast agents (study group, n = 6) and Gd-DTPA as non-specific contrast agents (control group, n = 4) was injected respectively into caudal vein of the nude mice which was pulmonary tumor xenografts as experimental model in the study. MRI was performed with plain scans, enhanced scans at 30 minutes, 3 hours, 6 hours, 14 hours, 24 hours, 38 hours, 48 hours, 62 hours and 72 hours after the success of injection. Signal intensities of tumors and muscles were measured. (1) folate-PL-Gd-DTPA was successfully synthesized with high affinity to folate receptor and high concentration of Gd(3+) (56 Gd(3+)/folate). (2) folate-PL-Gd-DTPA had an excellent tumor selectivity in pulmonary tumor xenografts in the animal model. After injection, the tumor signal intensity in the study group was significantly higher than that observed before injection; An average intensity increase of 125.4% was observed from pre-contrast to post-contrast images of the tumor, which was observed at 24 - 48 hours after injection; The muscle signal intensity at any time-point after injection showed no statistically difference with that observed before injection. In control group, the tumor signal intensity showed statistically difference with that observed before injection at 0.5 hour and 3 hours, the biggest difference appeared at 0.5 hour; The muscle signal intensity at 0.5 hour time-point showed statistically difference with that observed before injection. Folate-PL-Gd-DTPA could be combined to tumor cells appetencially via folate receptor and significantly targeted to tumor cells with rich folate receptors for MR imaging.

Gd nanoparticulates: from magnetic resonance imaging to neutron capture therapy

Abstract —Gadolinium (Gd) chelates have been extensively applied to enhance the imagery of anatomical tissues via magnetic resonance imaging (MRI). These molecular complexes have become some of the most common clinically applied contrast agents in modern medicine. The expansive development and clinical application of Gd chelates for MRI applications has led to are birth of interest in the use of Gd as a radiosensitizer in neutron capture therapy (NCT). However, the poor selective tissue labeling and localization provided by conventional molecular Gd chelates has limited success in both MRI and NCT applications. Methods for encapsulating Gd into nanoparticulate materials have been developed to overcome these limitations. Incorporating Gd chelates into nanoparticulate materials affordsadditional flexibility in engineering targeting and also providesa meansto apply high tissue-centric concentrations of Gd — often critical for both imaging and therapeutic applications. The focus of this review is to summarize the evolution of engineered Gd nanoparticles, from self-assembled macromolecular structures to rigid particulate systems for enhanced MRI contrast and, separately, Gd NCT therapy.

Electroluminescence properties of the Gd3+ ultraviolet luminescent centers in SiO2 gate oxide layers

Electroluminescence (EL) properties in the ultraviolet (UV) range were studied on Gd-implanted indium tin oxide/SiO2:Gd∕Si metal-oxide-semiconductor light emitting devices. The efficient UV line at 316nm from Gd3+ centers shows a maximum power density of 2mW∕cm2 and a quantum efficiency above 5%. The Gd3+ luminescent center has an excitation cross section above 7.4×10−15cm2 with an EL decay time around 1.6ms at a Gd concentration of 3%. A decrease of the EL efficiency is observed by a cross relaxation at a high Gd concentration and by clustering of Gd atoms at an annealing temperature of 1000°C. A strong quenching of the UV EL due to electron trapping around optically active Gd3+ centers is observed during the injection of hot electrons.

Dual signaling is differentially activated by different active states of the metabotropic glutamate receptor 1alpha.

The metabotropic glutamate receptor 1alpha (mGluR1alpha) is crucial for some forms of synaptic plasticity, by inducing various cell responses via coupling to various types of G proteins. Upon glutamate binding, an active conformation, closed-open/active, of the extracellular domain is stabilized, which induces dimeric rearrangement in the intracellular domains, resulting in the initiation of downstream signals. We have confirmed that mGluR1alpha functionally interacts with both Gq and Gs pathways; a combination of fluorescent indicators showed that glutamate increased intracellular Ca(2+) and cAMP concentration ([Ca(2+)](i) and [cAMP](i)). By contrast, Gd(3+), a different type of ligand whose recognition site on mGluR1alpha is distinct from the glutamate site, increased only [Ca(2+)](i) and the concentration-activation curve was bell-shaped. FRET analysis revealed that a low concentration of Gd(3+) induced dimeric rearrangement of the intracellular domains of mGluR1alpha as does glutamate, whereas a high concentration of Gd(3+) reversed the FRET efficiency, which was consistent with a bell-shaped relationship between concentration and Gq activation. These results suggest that Gd(3+) induces an active and a sort of "inactivated" conformation in mGluR1alpha. The Gd(3+)-induced active state is considered to correspond to the closed-closed/active conformation, revealed by previous x-ray crystallographic studies. In conclusion, the glutamate-induced closed-open/active state coupled both to Gs and Gq proteins whereas the Gd(3+)-induced closed-closed/active conformation state preferred Gq to Gs, suggesting that mGluR1alpha serves not only as a simple on/off switch but also as a multiple signaling path regulator.

Liquid Crystal Dispersions of DNA Complexes with Gadolinium As a Possible Basis for Neutron-Trapping Therapy

Neutron-trapping therapy (NTT) is a method for treating malignant tumors based on neutron trapping by nonradioactive elements exposed to thermal neutrons [1]. Gadolinium (Gd) is one of these nonradioactive elements. In the case of Gd NTT, a 157 Gd preparation administered in vivo is used for the neutron-trapping reaction. The neutron-trapping nuclear reaction ( 157 Gd ( n , γ ) 158 Gd ) is accompanied by the appearance of γ quanta and Auger electrons destroying the tumor tissue [1] and damaging the DNA of neoplastic cells [2]. The key factor of the success of Gd NTT is to obtain nontoxic [3, 4] molecular constructions [5–8] capable of maintaining a high concentration of Gd 3+ after the substance has been administered into the tumor. Special attention is paid to various nanoparticles containing Gd 3+ [4, 9, 10].

Engineering tumor-targeted gadolinium hexanedione nanoparticles for potential application in neutron capture therapy.

Microemulsions (oil-in-water) have been employed as templates to engineer nanoparticles containing high concentrations of gadolinium for potential application in neutron capture therapy of tumors. Gadolinium hexanedione (GdH), synthesized by complexation of Gd(3+) with 2,4-hexanedione, was used as the nanoparticle matrix alone or in combination with either emulsifying wax or PEG-400 monostearate. Solid nanoparticles (<125 nm size) were obtained by simple cooling of the microemulsions prepared at 60 degrees C to room temperature in one vessel. The feasibility of tumor targeting via folate receptors was studied. A folate ligand was synthesized by chemically linking folic acid to distearoylphosphatidylethanolamine (DSPE) via a poly(ethylene glycol) (PEG; MW 3350) spacer. To obtain folate-coated nanoparticles, the folate ligand (0.75% w/w to 15% w/w) was added to either the microemulsion templates at 60 degrees C or nanoparticle suspensions at 25 degrees C. Efficiencies of folate ligand attachment/adsorption to nanoparticle formulations were monitored by gel permeation chromatography. Cell uptake studies were carried out in KB cells (human nasopharyngeal epidermal carcinoma cell line), known to overexpress folate receptors. The uptake of folate-coated nanoparticles was about 10-fold higher than uncoated nanoparticles after 30 min at 37 degrees C. The uptake of folate-coated nanoparticles at 4 degrees C was 20-fold lower than the uptake at 37 degrees C and comparable to the uptake of uncoated nanoparticles at 37 degrees C. Folate-mediated endocytosis was further verified by the inhibition of folate-coated nanoparticles uptake by free folic acid. It was observed that folate-coated nanoparticles uptake decreased to approximately 2% of its initial value with the coincubation of 0.001 mM of free folic acid. The results suggested that these tumor-targeted nanoparticles containing high concentrations of Gd may have potential for neutron capture therapy.

Stretch-independent activation of the mechanosensitive cation channel in oocytes of Xenopus laevis

Oocytes of the South African clawed toad Xenopus laevis possess in their plasma membrane a so-called stretch-activated cation channel (SAC) which is activated by gently applying positive or negative pressure (stretch) to the membrane patch containing the channels. We show here that this mechanosensitive channel acted as a spontaneously opening, stretch-independent non-selective cation channel (NSCC) in more than half of the oocytes that we investigated. In 55% of cell-attached patches (total number of patches, 58) on 30 oocytes from several different donors, we found NSCC opening events. These currents were increased by elevating the membrane voltage or raising the temperature. NSCC and SAC currents shared some properties regarding the relative conductances of Na +>Li +>Ca 2+, gating behaviour and amiloride sensitivity. Stretch-independent currents could be clearly distinguished from stretch induced SAC currents by their voltage and temperature dependence. Open events of NSCC increased strongly when temperature was raised from 21 to 27°C. NSCC currents could be partly inhibited by high concentrations of extracellular Gd 3+ and amiloride (100 and 500 μM, respectively). We further show exemplarily that NSCC can seriously hamper investigations when oocytes are used for the expression of foreign ion channels. In particular, NSCC complicated investigations on cation channels with small conductance as we demonstrate for a 4 pS epithelial Na + channel (ENaC) from guinea pig distal colon. Our studies on NSCCs suggest the involvement of these channels in oocyte temperature response and ion transport regulation. From our results we suggest that NSCC and SAC currents are carried by one protein operating in different modes.

The magnetic phase diagram and the effect of pressure on the magnetic properties of the intermetallic compounds

The magnetization up to 50 kOe, the magnetic susceptibility under external pressure up to 5 kbar and the thermal expansion of the cubic Laves phase compounds were studied over a wide temperature range. Two well defined concentration regions were isolated in the x-T phase diagram: , in which the antiferromagnetic structure is primarily determined by the d-d interaction (-type), and , in which the f-d interaction plays a dominant role (-type). It is concluded that both the Gd and the Mn sublattices are ordered in below , the change in the magnetic characteristics at 40 K being interpreted as an antiferromagnetism-non-collinear ferrimagnetism transition. The intermediate compound shows a freezing and time-dependent behaviour at low temperatures characteristic of short-range order. The effects can also be induced by external pressure at higher Gd concentrations.

Perpendicular Magnetic Anisotropy in CoGd/Pd Multilayered Films

The magnetic properties of sputtered RE-TM(CoGd)/Pd multilayered films were studied. CoGd layers with high Gd concentration were amorphous. Reducing the Gd concentration, CoGd layers changed from amorphous to crystalline gradually. Like in the crystalline Co/Pd multilayered films, perpendicular magnetic anisotropy (PMA) was observed only for CoGd/Pd multilayered films with thin magnetic layer. It is interesting to note that the critical magnetic layer thickness, below which the easy magnetization axis is perpendicular to the film plane, reaches 2.5 nm for CoGd/Pd multilayered films with amorphous CoGd layers and is larger than that of Co/Pd multilayered films. The PMA energy density of CoGd layers was much higher than that of amorphous CoGd films. These results are discussed in terms of the perpendicular magnetization mechanism in amorphous CoGd films as well as of interface magnetic anisotropy.