  Multiferroic materials, which simultaneously exhibit ferroelectricity and
magnetism, have attracted substantial attention due to their fascinating
physical properties and potential technological applications. With the trends
towards device miniaturization, there is an increasing demand for the
persistence of multiferroicity in single-layer materials at elevated
temperatures. Here, we report high-temperature multiferroicity in single-layer
CuCrSe$_2$, which hosts room-temperature ferroelectricity and 120 K
ferromagnetism. Notably, the ferromagnetic coupling in single-layer CuCrSe$_2$
is enhanced by the ferroelectricity-induced orbital shift of Cr atoms, which is
distinct from both types I and II multiferroicity. These findings are supported
by a combination of second-harmonic generation, piezo-response force
microscopy, scanning transmission electron microscopy, magnetic, and Hall
measurements. Our research provides not only an exemplary platform for delving
into intrinsic magnetoelectric interactions at the single-layer limit but also
sheds light on potential development of electronic and spintronic devices
utilizing two-dimensional multiferroics.
