Speaker
Description
Motivation
The tetragonal distortion in spinel structures, such as CuFe$_2$O$_4$, CuCr$_2$O$_4$, and NiCr$_2$O$_4$, has garnered significant attention due to its profound influence on structural and magnetic properties [1]. Among these, CuFe$_2$O$_4$ is unique as it is ferromagnetic at room temperature. The tetragonal distortion in CuFe$_2$O$_4$ has been explained using semicovalent bonding [2] and the Jahn-Teller effect [3].
The transition from a tetragonal to a cubic structure upon heating has been the subject of ongoing research. Bertaut [4] initially proposed a transition temperature of 760°C, but subsequent studies by Miyahara and Ohnishi [5] using high-temperature X-ray diffraction and heat analysis corrected this value to approximately 400°C. This transition occurs below the magnetic Curie temperature, highlighting the coupling between structural and magnetic properties. Additionally, Takei et al. [6] and Forrer et al. [7] observed anomalies near 390°C, consistent with this structural phase transition. These findings motivate further studies on CuFe$_2$O4 to understand its temperature-dependent structural transitions, magnetoelastic coupling, and associated changes in elastic constants. Such investigations provide key insights into the material’s fundamental physics and potential applications in magnetostrictive and multiferroic devices.
Findings and future plan
CuFe$_2$O$_4$ demonstrates complex structural and acoustic transitions driven by temperature variations. The tetrahedral structure transitions to a cubic phase with increasing temperature as evidenced by X-ray diffraction. Elastic neutron scattering reveals temperature-induced changes in the Lorentzian scale and width. The scale decreases with increasing temperature, while the width broadens, indicating evolving elastic properties. These trends align with fitting models, confirming the consistency of our interpretation.
Inelastic neutron scattering along $\mathbf{Q}=[1,\bar{1},0]$ at room temperature reveals the relationship between the Lorentzian peak position and the acoustic rate. The acoustic rate, defined by the Lorentzian peak position, is directly linked to the elastic constant $c_{11}$-$c_{12}$. Shifts in the Lorentzian peak position and width with increasing temperature provide insights into the softening of elastic constants, with our fittings confirming these trends.
Future experiments will refine the understanding of these transitions, expanding measurements of elastic constants and exploring scattering along additional directions. These efforts aim to advance knowledge of the interplay between structural, acoustic, and magnetic properties in CuFe$_2$O$_4$.
[1] T. Inoue and S. Iida. Specific heats of copper ferrite. J. Phys. Soc. Japan, 13, 1958.
[2] J. B. Goodenough and A. L. Loeb. Specific heats of copper ferrite. Phys. Rev., 98:391,
1955.
[3] J. D. Dunitz and L. E. Orgel. Jahn-teller effect and the structure of copper ferrite.
J. Phys. Chem. Solid., 3:20, 1957.
[4] E. F. Bertaut. Structural transitions in cufe2o4. Compt. Rend., 230:213, 1950.
[5] S. Miyahara and H. Ohnishi. The phase transition in cufe2o4 as observed by x-ray
diffraction at high temperature. J. Phys. Soc. Japan, 12:1296, 1956.
[6] T. Yasuda T. Takei and S. Ishihara. Anomalous behavior of magnetization in cufe2o4.
Denkigakkai Shi in Japan, 59:568, 1939.
[7] R. Baffle R. Forrer and P. Fourinier. Magnetic properties of copper ferrites. J. de Phys., 6:71, 1945.
