Magnetic anisotropy and entropy change in trigonal ${\mathrm{Cr}}_5{\mathrm{Te}}_8$

We present a comprehensive investigation of the anisotropic magnetic and magnetocaloric properties of quasi-two-dimensional weak itinerant ferromagnet trigonal ${\mathrm{Cr}}_5{\mathrm{Te}}_8$ single crystals. Magnetic-anisotropy-induced satellite transition $T^{*}$ is observed at low fields applied parallel to the $ab$ plane below the Curie temperature ($T_c\sim 230\mathrm{K}$). $T^{*}$ is featured by an anomalous magnetization downturn, similar to that in structurally related ${\mathrm{CrI}}_3$, which possibly stems from an in-plane antiferromagnetic alignment induced by out-of-plane ferromagnetic spins canting. Magnetocrystalline anisotropy is also reflected in magnetic entropy change $\mathrm{\Delta }{S}_M(T,H)$ and relative cooling power. Given the high Curie temperature, ${\mathrm{Cr}}_5{\mathrm{Te}}_8$ crystals are materials of interest for nanofabrication in basic science and applied technology.

Figure 1

(a) Refinement of synchrotron x-ray diffraction data of ${\mathrm{Cr}}_5{\mathrm{Te}}_8$: data (solid symbols), structural model (red solid line), difference curve (blue solid line, offset for clarity). Vertical tick marks denote reflections in the main phase (black, top row) and the secondary Te impurity (red, bottom row). (b) Normalized Cr $K$-edge XANES spectra and (c) Fourier transform magnitudes of EXAFS data of ${\mathrm{Cr}}_5{\mathrm{Te}}_8$ taken at room temperature. The experimental data are shown as blue symbols alongside the model fit plotted as a red line. The inset in (c) shows the corresponding EXAFS oscillation with the model fit.

Figure 2

(a)–(d) Temperature dependence of zero-field-cooling (ZFC) and field-cooling (FC) magnetization of ${\mathrm{Cr}}_5{\mathrm{Te}}_8$ measured at indicated fields applied along the $c$ axis. (e) Temperature-dependent $dM/dT$ derived from FC curves with $\mathbf{H}\parallel \mathbf{c}$. (f)–(i) Temperature dependence of ZFC and FC magnetization of ${\mathrm{Cr}}_5{\mathrm{Te}}_8$ measured at indicated fields applied in the $ab$ plane. (j) Temperature-dependent $dM/dT$ derived from FC curves with $\mathbf{H}\parallel \mathbf{ab}$.

Figure 3

Magnetization as a function of field at various temperatures for (a) $\mathbf{H}\parallel \mathbf{c}$ and (b) $\mathbf{H}\parallel \mathbf{ab}$, respectively. ac susceptibility real part (c) $m^{\prime }\left(T\right)$ and (d) imaginary part $m^{\prime \prime }\left(T\right)$ as a function of temperature measured with an oscillated ac field of 3.8 Oe and a frequency of 499 Hz applied in the $ab$ plane and along the $c$ axis, respectively.

Figure 4

Typical initial isothermal magnetization curves from $T=200$ to 280 K with temperature steps of 4 K measured (a) in the $ab$ plane and (b) along the $c$ axis, respectively. (c) Temperature-dependent anisotropy constant $K_u$ (left axis) and the ratios of ${[M_s/M_s\left(160\text{K}\right)]}^{n(n+1)/2}$ with $n=1$, 2, and 4 (right axis).

Figure 5

Temperature dependence of magnetic entropy change $-\mathrm{\Delta }{S}_M$ obtained from magnetization measurement at various magnetic field changes (a) in the $ab$ plane and (b) along the $c$ axis, respectively. The inset shows the field dependence of $-\mathrm{\Delta }{S}_M$ at low temperature. The rotational magnetic entropy change $-\mathrm{\Delta }{S}_M^R$ as a function of (c) temperature and (d) field.

Figure 6

(a) Temperature dependence of $p$ in various fields. (b) Field dependence of the maximum magnetic entropy change $-\mathrm{\Delta }{S}_M^{\text{max}}$ and the relative cooling power (RCP) with power-law fitting in red solid lines. (c) The normalized $\mathrm{\Delta }{S}_M$ as a function of the rescaled temperature $\theta$ with out-of-plane field and in-plane field (inset). (d) Scaling plot of $\mathrm{\Delta }{S}_M$ based on the critical exponents $\beta =0.315$ and $\gamma =1.81$ [19]. The inset shows $T_r$ vs $H^{1/\mathrm{\Delta }}$ with $\mathrm{\Delta }=\beta +\gamma$.