Magnetic and magnetothermal studies of pure and doped gadolinium silicide nanoparticles for self-controlled hyperthermia applications

Highlights: • First report on magnetic hyperthermia in Gd₅Si₄ nanoparticles. • High SAR and low T_C ∼ 315–320 K; potential for self-controlled hyperthermia. • Gd₅Si₄ nanoparticles act as self-regulating heat switches. • Zero M_R and H_C near zero field highly desirable for biomedical applications. We report on magnetic and magnetothermal properties of undoped and doped gadolinium silicide (Gd₅Si₄) nanoparticles with the objective of simultaneously attaining high specific absorption rate (SAR) and low Curie temperature (T_C) suitable for self-controlled hyperthermia applications for which T_C ∼ 315–320 K. Pellets of doped gadolinium silicide Gd₅(Si_1−xGe_x)₄ and (Gd_1−xR_x)₅Si₄ with R = Ho, Nd and Er and 0 ≤ x ≤ 0.35 were made by arc melting and reduced to nanoparticulate form by surfactant assisted ball milling. Structural and morphological studies were done using X-ray diffraction and scanning electron microscopy respectively. All samples show soft magnetic properties. At low fields there is a ferromagnetic to paramagnetic transition that reduces remanance and coercivity to zero making these materials very attractive for biomedical applications. Zero-field-cooled thermal demagnetization measurements showed that T_C of these nanoparticles can be lowered to lie within the limits required for self-controlled hyperthermia by varying the dopant concentration. Specific absorption rates (SAR's) were obtained from magnetothermia measurements made in an ac magnetic field of amplitude 10 Oe and frequency 300 kHz. We have identified samples that have SAR values larger or comparable to those of magnetite and several ferrite nanoparticles, while having Curie temperatures that are low enough for self controlled hyperthermia applications.