Rare Earth – Transition Metal Magnetic Multilayer Systems

One of the most long-standing research lines of the GMM is the study of magnetic multilayers (MLs) obtained by sputtering of Rare Earths and Transition Metals. Specifically, Gd/Co multilayers have been studied. These two materials are ferromagnetic, but they exhibit a perfectly antiparallel coupling between them. Combined with their different ordering temperatures, this results in a great variety of magnetic configurations in these MLs.

The GMM has extensively worked on experimentally obtaining these magnetic multilayers and studying and characterizing their structural, magnetic, and electrical transport properties. Experimentally, these MLs present the challenge of strong asymmetric interdiffusion between Gd and Co during the growth process. This results in MLs composed of amorphous GdCo and Co alloys, making their study more complex. The GMM has developed a process to achieve MLs with high structural quality and well-defined interfaces between layers by replacing pure Gd with GdCo alloys.

All these studies have resulted in several scientific articles and two doctoral theses by members of the GMM:

• “Structural and Magnetic Characterization of the Gd/Co System” by Juan Pedro Andrés González (2000)
• “Interdiffusion, Magnetic Properties, and Electrical Transport in Gd/Co-Based Multilayers” by Juan Antonio González Sanz (2002).

Magnetic Nanoparticles

A second major line of research has focused on the fabrication and study of magnetic nanoparticles (NPs). In this field, research has been conducted on the following topics:

• Study of Interactions Between Particles: 

Initially, research focused on frustrated multilayers, where a magnetic layer was made so thin that it broke apart, generating dispersed particles within a metallic matrix. Different magnetic interactions (dipolar, indirect RKKY) between the particles were studied depending on the material separating them.

• Core–Shell Structured Nanoparticles:

Through controlled oxidation processes, Co–CoO core-shell structured NPs were generated. Due to the antiferromagnetic nature of CoO and the ferromagnetic behavior of Co, these NPs exhibit a pronounced Exchange-Bias effect, which holds significant potential for technological applications.

• NPs Obtained by Gas-Phase Aggregation (Cluster-Gun):

A facility equipped with a nanoparticle gun (cluster-gun) has been developed, allowing the generation of NPs using gas-phase aggregation techniques. This method provides precise control over the size and characteristics of the NPs. The facility enables the production of NP films as well as NP systems embedded in other material matrices. Studies have been conducted on Co/CoO particles by controlling the oxidation of pure Co NPs, as well as investigating the effect of different matrices on the properties of these NPs, particularly in relation to the Exchange-Bias phenomenon.

Heterostructures of Magnetic and Multiferroic Oxides

The most recent research line initiated by the group focuses on the construction of a new sputtering facility for the deposition of ceramic oxides. Specifically, the goal is to obtain multilayer heterostructures that enable the control of the magnetic state of a ferromagnetic cobaltite layer (LaSrCoO₃) through the antiferromagnetic nature of multiferroic oxides such as YMnO₃ and RMnO₃ (R = Dy, Lu). This interaction gives rise to an Exchange-Bias effect with the ferromagnetic cobaltite.