Most of the spiral magnetoelectric multiferroics investigated in recent years are geometrically or exchange frustrated magnets with low magnetic transition temperatures. The exceptional stability of the spiral magnetic order (at T$_S$) in the layered structure of YBaCuFeO$_5$ [1,2] involves a non-conventional mechanism (“spiral order by disorder”) theoretically developed by Scaramucci et al. . Using neutrons we have investigated the impact of tuning frustration through B-site disorder (n$_d$) on the magnetic spiral phase in the reference compound YBaCuFeO$_5$  The influence of disorder (and only disorder) on the magnetic phase diagram is studied on a quantitative basis. The interplay between disorder, stability and the detailed features of the incommensurate spiral magnetic orders has been investigated in samples of identical composition, spanning a wide range of n$_d$ values. Three different regimes are distinguished in the YBaCuFeO$_5$ phase diagram versus disorder, which set limits to T$_S$ and the cycloidal component of the helicoidal order [4,5]. This layered structure appears as a very efficient realization of the new avenue to supply functional helimagnets at normal working temperatures.
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