We report the magnetic and magnetostrictive behaviors of the pseudobinary ferrimagnetic spinel oxide system (1−x)CoFe2O4–xCoAl2O4 [Co(Fe1−xAlx)2O4], with one end-member being the ferrimagnetic CoFe2O4 and the other end-member being CoAl2O4 that is paramagnetic above 9.8 K. The temperature spectra of magnetization and magnetic susceptibility were employed to detect the magnetic transition temperatures and to determine the phase diagram of this system. Composition dependent and temperature dependent magnetostrictive behaviors reveal an exotic phase boundary that separates two ferrimagnetic states: At room temperature and under small magnetic fields (∼500 Oe), Fe-rich compositions exhibit negative magnetostriction while the Al-rich compositions exhibit positive magnetostriction though the values are small (<10 ppm). Moreover, the compositions around this phase boundary at room temperature (x = 0.35, 0.4, 0.45, 0.5) exhibit near-zero magnetostriction and enhanced magnetic susceptibility, which may be promising in the applications for magnetic cores, current sensors, or magnetic shielding materials.

Morphotropic phase boundary (MPB) have aroused wide interests due to the exotic properties exhibited by the compositions around MPB [Tb 1−x Dy x Co 2 , PRL 104, 197201 (2010); Tb 1−x Dy x Fe 2 , PRL 111, 017203 (2013)]. By combining the two MPB compositions Tb 0.3 Dy 0.7 Co 2 and Tb 0.3 Dy 0.7 Fe 2 , we designed a pseudo-binary system Tb 0.3 Dy 0.7 (Co 1−x Fe x ) 2 . The phase diagram is determined from the temperature spectra of magnetic susceptibility and magnetization. A Griffiths-like phase appears above the Curie temperature and gradually vanishes as the Fe content increases to x = 0.8. Magnetic hysteresis and magnetoelastic behavior are also investigated. Compared with the Terfenol-D composition x = 1.0, x = 0.8 exhibits higher Curie temperature (707 K) and comparable magnetostriction (818 ppm), which may be used in the sensors or transducers at high temperature.

Abstract