記憶 and 思い出: remembered information and personal experiences
Distinguish memory broadly from experiences recalled personally, and learn patterns with the noun 思い出.
What memory contains
記憶, read きおく, refers to memory or remembered information. 数字を記憶するのが得意です。 says that someone is good at remembering numbers.
あの声は記憶に残っています。 says that a particular voice remains in memory. It does not mean the voice is currently audible.
Looking back on personal experience
思い出, read おもいで, refers to memories of past experiences. 旅の思い出を話しました。 means talking about memories of a trip.
楽しい思い出も悲しい思い出もあります。 says that there are both happy and sad memories. 思い出 is not restricted to pleasant content.
Noun and verb
思い出を大切にしています。 means cherishing one's memories. 思い出 here is a noun marked by を.
思い出す is the verb for recalling, while 思い出 is the noun for a memory. In 旅行の思い出を思い出しました, the travel memories are what was recalled, and the final verb names the action.
Is 悲しい思い出 a possible expression?
Show the answer and why
Yes. 思い出 can include unhappy past experiences.