BCMaterials Fortnightly Seminars #43

DANIEL SALAZAR

(BCMaterials)

DIRECT AND INDIRECT MEASUREMENT OF MAGNETOCALORIC EFFECT IN LA-SR,BA MANGANITES

Perovskite manganites materials R_1-xA_xMnO₃ (R = La, Nd, Pr; A = Ca, Ba, Sr…) are interesting materials as they exhibit a vast variety of physical phenomena; for instance, some perovskite manganites present large magnetocaloric effect (MCE) with a magnetic entropy change (DS_M) even comparable to that of Gd.¹ Besides, changes in the dopant A or the rare earth modify their magnetic and MCE properties, a compelling feature that allows tuning the working temperature range.² In this work, we studied the MCE in three microcrystalline manganites of compositions La₇Ba_0.3MnO₃, La_0.7Sr_0.3MnO₃, and La_0.8Sr_0.2MnO₃ , which experience a second-order magnetic phase transition close to room temperature (between 300 and 350K) by direct and indirect techniques. We determined DS_M(T) from the specific heat curves at constant pressure measured at zero magnetic field and under magnetic fields of 1 and 2T, reaching a maximum around Curie point (T_C) of 3.1, 2.0, and 2.4J/(kg·K) under a field of 2T for La_0.8Sr_0.2MnO₃, La_0.7Sr_0.3MnO₃, and La_0.7Ba_0.3MnO₃ respectively, with refrigerant capacities up to 85J/kg. Direct measurement of adiabatic temperature change, DT_ad, were performed in a homemade system³ with a maximum magnetic field change of 1.9T and a temperature range between 220K and 450K. To monitor DT_ad, a thermocouple type T was embedded in the sample under test and the temperature was read during the experiment. DT_ad maximum was measured close to T_C for all specimens, with values ~1.5K for m₀DH=1.9T, in agreement to the results obtained indirectly from the specific heat (1.7, 1.2, and 1.5K for La_0.8Sr_0.2MnO₃, La_0.7Sr_0.3MnO₃, and La_0.7Ba_0.3MnO₃ respectively under a magnetic field change of 2T).^{4   1} M.-H. Phan and S.-C. Yu, J. Magn. Magn. Mater. 308, 325 (2007). ² I.K. Kamilov, et.al., J. Phys. D: Appl. Phys. 40, 4413 (2007). ³ P. Álvarez-Alonso, J. López-García, G. Daniel-Perez, D. Salazar, P. Lázpita, J.P. Camarillo, H. Flores-Zuñiga, D. Rios-Jara, J.L. Sánchez-Llamazares, and V.A. Chernenko, Key Eng. Mater. 644, 215 (2015). ⁴ D. Salazar, P. Álvarez-Alonso, M.A. López de la Torre, J.M. Barandiarán, 13^th Joint MMM-Intermag Conference, San Diego CA, January 2016.

 

---

IRATI RODRIGO

(BCMaterials)

DEVELOPMENT OF EXPERIMENTAL TECHNIQUES FOR MAGNETIC HYPERTHERMIA THERAPY

Magnetic hyperthermia is a cancer therapy, where magnetic nanoparticles placed inside the tumour act as heat sources activated by an externally applied magnetic field. These nanoparticles increase the temperature of tumour cells and induces the…. The increment of tumour`s temperature is a very important parameter to control during the hyperthermia treatment. An overheating of the tumour can result in serious damage to the surrounding healthy cells or in an uncontrolled necrosis. On the contrary, with an insufficient temperature increment, the desired therapeutic effects cannot be achieved. The SAR (Specific Absorption Rate) is a crucial parameter to determine the tissue temperature during the hyperthermia treatment. So, in order to understand the heating mechanism of the nanoparticles, accurate measurements of the SAR of nanoparticles are necessary. Our group has developed an accurate AC magnetometer which allow the quantification of SAR. In order to prove the effectivity of the treatment, is important to do in vitro and in vivo essays. We are part of a big collaboration group focus in magnetic hyperthermia treatment in colorectal cancer. Our work is to measure the SAR with an AC magnetometer and control the electromagnetic applicator that generates de magnetic field during the hyperthermia.