Room-temperature weak collinear ferrimagnet with symmetry-driven large intrinsic magneto-optic signatures

Here we present a magnetic thin film with a weak ferrimagnetic (FIM) phase above the Néel temperature ($T_N=240\mathrm{K}$) and a noncollinear antiferromagnetic (AFM) phase below, exhibiting a small net magnetization due to strain-associated canting of the magnetic moments. A long-range ordered FIM phase has been predicted in related materials, but without symmetry analysis. We now perform this analysis and use it to calculate the magneto-optical Kerr effect (MOKE) spectra in the AFM and FIM phases. From the good agreement between the form of the measured and predicted MOKE spectra, we propose the AFM and FIM phases share the magnetic space group $C{2}^{\prime }/m^{\prime }$ and that the symmetry-driven magneto-optic and magneto-transport properties are maximized at room temperature in the FIM phase due to the nonzero intrinsic Berry phase contribution present in these materials. A room temperature FIM with large optical and transport signatures, as well as sensitivity to lattice strain and magnetic field, has useful prospects for high-speed spintronic applications.

Figure 1

(a) The antiferromagnetic transition temperature $T_N=240\mathrm{K}$ identified from field-cooled (measured on both warming and cooling) and zero-field–cooled $M$($T$) in 50 mT. $M$($H$) is shown in (b), (c), and (d) at 300 K, 210 K, and 170 K, respectively. (e) The coercive field $H_c$($T$) for field in the plane of the film and out of the plane and the inset (f) showing the saturation magnetization in the two field directions. (g) The saturated anomalous Hall resistivity ${\rho }_{xy,\mathrm{sat}}\left(T\right)$ and the inset (h) show the longitudinal resistivity ${\rho }_{xx}\left(T\right)$ of the ${\mathrm{Mn}}_3\mathrm{NiN}$ film on BTO and STO substrates. ${\rho }_{xy,\mathrm{sat}}\left(T\right)$ is obtained by subtracting the ordinary Hall contribution.

Figure 2

(a) Schematic picture of the unit cell of ${\mathrm{Mn}}_3\mathrm{NiN}$ together with the manganese magnetic moment alignment in the noncollinear AFM phase. (b) Simplified picture of the magneto-optically active charge transfer electronic transitions from nickel to manganese $3d$ states. The arrows with the curly backets represent groups of transitions for I and II energy regions observed in manganese density of states (DOS). (c) Experimental spectra of polar MOKE rotation taken at 180 K, obtained from field-cooled measurements in $\pm 200\mathrm{mT}$. The yellow region is the position of the gap-like feature in manganese DOS taken from nickel states. (d) Ab initio calculated polar MOKE spectrum for the AFM phase and $U=0$ (black line) and 0.7 eV (red line); theory is multiplied by 0.1. (e) Element-resolved DOS for manganese $3d$ states with a marked gap-like feature. (f) Element-resolved DOS for nickel $3d$ states.

Figure 3

(a) Schematic picture of the unit cell of ${\mathrm{Mn}}_3\mathrm{NiN}$ together with the manganese magnetic moment alignment in the FIM phase. (b) Simplified picture of the magneto-optically active charge transfer electronic transitions from nickel to manganese $3d$ states. The arrow with the curly backet represents all transitions for the whole investigated energy region. (c) Experimental spectra of polar MOKE rotation taken at 300 K, obtained from data taken at $\pm 200\mathrm{mT}$. The yellow region is the position of the gap-like feature in manganese DOS of the AFM phase taken from nickel states. (d) Ab initio calculated polar MOKE spectrum for the FIM phase and $U=0$ (black line) and 0.7 eV (red line); theory is multiplied by 0.1. (e) Element-resolved DOS for manganese $3d$ states with marked gap-like feature in the AFM phase. (f) Element-resolved DOS for nickel $3d$ states.

Figure 4

(a) Schematic picture of the unit cell of ${\mathrm{Mn}}_3\mathrm{NiN}$ together with the manganese magnetic moment alignment across the transition from the AFM to FIM phase induced by the change of temperature. (b) Temperature evolution of experimental spectra of polar MOKE rotation, obtained from data taken at $\pm 200\mathrm{mT}$. The yellow region is the position of the gap-like feature in the manganese DOS of the AFM phase taken from nickel states. (c) Differential MOKE spectrum at 300 K to 180 K with marked position of the gap-like feature in the manganese DOS of the AFM phase. (d) Experimental MOKE spectrum taken at 210 K together with theoretical calculation when taking into account 60% of the AFM and 40% of the FIM phase; theory is multiplied by 0.1. (e) A comparison of the temperature evolution of AHE conductivity (red stars) and integrated MOKE (black circles) between 1.5 and 4.3 eV.