Er2Ti2O7
is
a
quantum
XY
pyrochlore
magnet
that
orders
into
a
non-linear,
non-coplanar
Néel
state
below
T=1.2
K
via
ground-state
selection
proposed
to
originate
from
an
order-by-disorder
mechanism
[1,2].
As
the
ground
state
selection
is
relatively
weak,
it
is
interesting
to
examine
its
stability
to
perturbations
such
as
magnetic
dilution
and
chemical
pressure.
Indeed,
recent
theory
strongly
suggests
rich
phase
diagrams
resulting
from
such
instabilities
[3,4,5,6].
Magnetic
dilution
was
achieved
by
substituting
a
small
fraction
of
the
Seff=1/2
Er3+
ions
for
non-magnetic
Y3+
ions;
while
chemical
pressure
resulted
from
the
replacement
of
non-magnetic
Ti4+
ions
within
the
pyrochlore
structure
by
other
non-magnetic
ions
such
as
Pt4+.
I
will
discuss
our
recent
experimental
results
[7,8],
with
a
focus
on
neutron
scattering,
where
these
chemical
perturbations
demonstrate
the
richness
of
the
phase
space
in
which
XY
pyrochlore
magnets,
such
as
Er2Ti2O7,
reside
-
a
consequence
of
anisotropic
exchange,
multiphase
competition,
and
order-by-disorder
effects.
[1]
L.
Savary
et
al.,
Phys.
Rev.
Lett.
109,
167201
(2012),
[2]
M.E.
Zhitomirsky
et
al.,
Phys.
Rev.
Lett.
109,
077204
(2012)
[3]
Maryasin,
V.
S.,
and
M.E.
Zhitomirsky,
Phys.
Rev.
B
90,
094412
(2014),
[4]
Andreanov,
A.,
and
P.
A.
McClarty,
Phys.
Rev.
B
91,
064401
(2015),
[5]
H.
Yan
et
al.,
Phys.
Rev.
B
95,
094422
(2017)
[6]
E.C.
Andrade
et
al.,
Phys.Rev.Lett
120,
097204
(2018),
[7]
J.
Gaudet
et
al.,
Phys.
Rev.
B
94,
060407(R)
(2016),
[8]
A.
M.
Hallas
et
al.,
Phys.
Rev.
Lett.
119,
187201
(2017)